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16<!--#include virtual="../menu.html.incl"-->
17
18<div id="content">
19
20<h1>Clang Compiler User's Manual</h1>
21
22<ul>
23<li><a href="#intro">Introduction</a>
24 <ul>
25 <li><a href="#terminology">Terminology</a></li>
26 <li><a href="#basicusage">Basic Usage</a></li>
27 </ul>
28</li>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]29<li><a href="#commandline">Command Line Options</a>
30 <ul>
31 <li><a href="#cl_diagnostics">Options to Control Error and Warning
32 Messages</a></li>
33 </ul>
34</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]35<li><a href="#general_features">Language and Target-Independent Features</a>
36 <ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]37 <li><a href="#diagnostics">Controlling Errors and Warnings</a>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]38 <ul>
39 <li><a href="#diagnostics_display">Controlling How Clang Displays Diagnostics</a></li>
40 <li><a href="#diagnostics_mappings">Diagnostic Mappings</a></li>
Chris Lattner67db8cd2010-05-30 23:42:51 +0000[diff] [blame]41 <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]42 <li><a href="#diagnostics_commandline">Controlling Diagnostics via Command Line Flags</a></li>
43 <li><a href="#diagnostics_pragmas">Controlling Diagnostics via Pragmas</a></li>
Ted Kremenekf391fa72011-08-18 01:17:05 +0000[diff] [blame]44 <li><a href="#diagnostics_enable_everything">Enabling All Warnings</a></li>
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]45 <li><a href="#analyzer_diagnositics">Controlling Static Analyzer Diagnostics</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]46 </ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]47 </li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]48 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]49 <li><a href="#codegen">Controlling Code Generation</a></li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]50 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]51</li>
52<li><a href="#c">C Language Features</a>
53 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]54 <li><a href="#c_ext">Extensions supported by clang</a></li>
55 <li><a href="#c_modes">Differences between various standard modes</a></li>
56 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
57 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
58 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]59 </ul>
60</li>
Richard Smithbdb10182011-11-21 20:54:59 +0000[diff] [blame]61<li><a href="#cxx">C++ Language Features</a>
62 <ul>
63 <li><a href="#cxx_implimits">Controlling implementation limits</a></li>
64 </ul>
65</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]66<li><a href="#target_features">Target-Specific Features and Limitations</a>
67 <ul>
68 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
69 <ul>
70 <li><a href="#target_arch_x86">X86</a></li>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]71 <li><a href="#target_arch_arm">ARM</a></li>
72 <li><a href="#target_arch_other">Other platforms</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]73 </ul>
74 </li>
75 <li><a href="#target_os">Operating System Features and Limitations</a>
76 <ul>
77 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
78 <li>Linux, etc.</li>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]79 <li><a href="#target_os_win32">Windows</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]80 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]81 </li>
82 </ul>
83</li>
84</ul>
85
86
87<!-- ======================================================================= -->
88<h2 id="intro">Introduction</h2>
89<!-- ======================================================================= -->
90
91<p>The Clang Compiler is an open-source compiler for the C family of programming
92languages, aiming to be the best in class implementation of these languages.
93Clang builds on the LLVM optimizer and code generator, allowing it to provide
94high-quality optimization and code generation support for many targets. For
95more general information, please see the <a href="http://clang.llvm.org">Clang
96Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
97
98<p>This document describes important notes about using Clang as a compiler for
99an end-user, documenting the supported features, command line options, etc. If
100you are interested in using Clang to build a tool that processes code, please
101see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
Michael J. Spencer8275fc02012-02-12 09:11:39 +0000[diff] [blame]102interested in the <a href="http://clang-analyzer.llvm.org">Clang
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]103Static Analyzer</a>, please see its web page.</p>
104
105<p>Clang is designed to support the C family of programming languages, which
106includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
107href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
108dialects of those. For language-specific information, please see the
109corresponding language specific section:</p>
110
111<ul>
112<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
113 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
114<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
115 variants depending on base language.</li>
Richard Smithbdb10182011-11-21 20:54:59 +0000[diff] [blame]116<li><a href="#cxx">C++ Language</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]117<li><a href="#objcxx">Objective C++ Language</a></li>
118</ul>
119
120<p>In addition to these base languages and their dialects, Clang supports a
121broad variety of language extensions, which are documented in the corresponding
122language section. These extensions are provided to be compatible with the GCC,
123Microsoft, and other popular compilers as well as to improve functionality
124through Clang-specific features. The Clang driver and language features are
125intentionally designed to be as compatible with the GNU GCC compiler as
126reasonably possible, easing migration from GCC to Clang. In most cases, code
127"just works".</p>
128
129<p>In addition to language specific features, Clang has a variety of features
130that depend on what CPU architecture or operating system is being compiled for.
Douglas Gregorcd5a5052009-11-09 15:15:41 +0000[diff] [blame]131Please see the <a href="#target_features">Target-Specific Features and
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]132Limitations</a> section for more details.</p>
133
134<p>The rest of the introduction introduces some basic <a
135href="#terminology">compiler terminology</a> that is used throughout this manual
136and contains a basic <a href="#basicusage">introduction to using Clang</a>
137as a command line compiler.</p>
138
139<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
140<h3 id="terminology">Terminology</h3>
141<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
142
143<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
144 optimizer</p>
145
146<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
147<h3 id="basicusage">Basic Usage</h3>
148<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
149
150<p>Intro to how to use a C compiler for newbies.</p>
151<p>
152compile + link
153
154compile then link
155
156debug info
157
158enabling optimizations
159
160picking a language to use, defaults to C99 by default. Autosenses based on
161extension.
162
163using a makefile
164</p>
165
166
167<!-- ======================================================================= -->
168<h2 id="commandline">Command Line Options</h2>
169<!-- ======================================================================= -->
170
171<p>
172This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]173depth on the ones that are covered by other sections. However, the first part
174introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]175</p>
176
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]177
178<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
179<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
180<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
181
182<p><b>-Werror</b>: Turn warnings into errors.</p>
183<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
184<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
185 specified.</p>
186<p><b>-Wfoo</b>: Enable warning foo</p>
187<p><b>-Wno-foo</b>: Disable warning foo</p>
188<p><b>-w</b>: Disable all warnings.</p>
189<p><b>-pedantic</b>: Warn on language extensions.</p>
190<p><b>-pedantic-errors</b>: Error on language extensions.</p>
191<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
192
Chris Lattner0f0c9632010-04-07 20:49:23 +0000[diff] [blame]193<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
194 been produced. The default is 20, and the error limit can be disabled with
195 -ferror-limit=0.</p>
196
Douglas Gregor575cf372010-04-20 07:18:24 +0000[diff] [blame]197<p><b>-ftemplate-backtrace-limit=123</b>: Only emit up to 123 template instantiation notes within the template instantiation backtrace for a single warning or error. The default is 10, and the limit can be disabled with -ftemplate-backtrace-limit=0.</p>
198
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]199<!-- ================================================= -->
200<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
201<!-- ================================================= -->
202
203<p>Clang aims to produce beautiful diagnostics by default, particularly for new
204users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]205preferences, and sometimes Clang is driven by another program that wants to
206parse simple and consistent output, not a person. For these cases, Clang
207provides a wide range of options to control the exact output format of the
208diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]209
210<dl>
211
212<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
213<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
214diagnostic.</dt>
215<dd>This option, which defaults to on, controls whether or not Clang prints the
216column number of a diagnostic. For example, when this is enabled, Clang will
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]217print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]218
219<pre>
220 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
221 #endif bad
222 ^
223 //
224</pre>
225
226<p>When this is disabled, Clang will print "test.c:28: warning..." with no
227column number.</p>
228</dd>
229
230<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
231<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
232source file/line/column information in diagnostic.</dt>
233<dd>This option, which defaults to on, controls whether or not Clang prints the
234filename, line number and column number of a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]235when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]236
237<pre>
238 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
239 #endif bad
240 ^
241 //
242</pre>
243
244<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
245</dd>
246
247<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
248<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
249line and ranges from source code in diagnostic.</dt>
250<dd>This option, which defaults to on, controls whether or not Clang prints the
251source line, source ranges, and caret when emitting a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]252when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]253
254<pre>
255 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
256 #endif bad
257 ^
258 //
259</pre>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]260</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]261<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]262<dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
263<dd>This option, which defaults to on when a color-capable terminal is
264 detected, controls whether or not Clang prints diagnostics in color.
265 When this option is enabled, Clang will use colors to highlight
266 specific parts of the diagnostic, e.g.,
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]267 <pre>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]268 <b><span style="color:black">test.c:28:8: <span style="color:magenta">warning</span>: extra tokens at end of #endif directive [-Wextra-tokens]</span></b>
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]269 #endif bad
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]270 <span style="color:green">^</span>
271 <span style="color:green">//</span>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]272</pre>
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]273
274<p>When this is disabled, Clang will just print:</p>
275
276<pre>
277 test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
278 #endif bad
279 ^
280 //
281</pre>
282</dd>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]283<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregorc9471b02011-05-21 17:07:29 +0000[diff] [blame]284<dt id="opt_fdiagnostics-format"><b>-fdiagnostics-format=clang/msvc/vi</b>:
285Changes diagnostic output format to better match IDEs and command line tools.</dt>
286<dd>This option controls the output format of the filename, line number, and column printed in diagnostic messages. The options, and their affect on formatting a simple conversion diagnostic, follow:
287
288 <dl>
289 <dt><b>clang</b> (default)</dt>
290 <dd>
291 <pre>t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
292 </dd>
293
294 <dt><b>msvc</b></dt>
295 <dd>
296 <pre>t.c(3,11) : warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
297 </dd>
298
299 <dt><b>vi</b></dt>
300 <dd>
301 <pre>t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
302 </dd>
303 </dl>
304</dd>
305
306<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Argyrios Kyrtzidis477aab62011-05-25 05:05:01 +0000[diff] [blame]307<dt id="opt_fdiagnostics-show-name"><b>-f[no-]diagnostics-show-name</b>:
308Enable the display of the diagnostic name.</dt>
309<dd>This option, which defaults to off, controls whether or not
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]310Clang prints the associated name.<p></p></dd>
Argyrios Kyrtzidis477aab62011-05-25 05:05:01 +0000[diff] [blame]311<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]312<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
313Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
314<dd>This option, which defaults to on,
315controls whether or not Clang prints the associated <A
316href="#cl_diag_warning_groups">warning group</a> option name when outputting
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]317a warning diagnostic. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]318
319<pre>
320 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
321 #endif bad
322 ^
323 //
324</pre>
325
326<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
327the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
328diagnostic. This information tells you the flag needed to enable or disable the
329diagnostic, either from the command line or through <a
330href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
331
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]332<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
333<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
334Enable printing category information in diagnostic line.</dt>
335<dd>This option, which defaults to "none",
336controls whether or not Clang prints the category associated with a diagnostic
337when emitting it. Each diagnostic may or many not have an associated category,
338if it has one, it is listed in the diagnostic categorization field of the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]339diagnostic line (in the []'s).
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]340
341<p>For example, a format string warning will produce these three renditions
342based on the setting of this option:</p>
343
344<pre>
345 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
346 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
347 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
348</pre>
349
350<p>This category can be used by clients that want to group diagnostics by
351category, so it should be a high level category. We want dozens of these, not
352hundreds or thousands of them.</p>
353</dd>
354
355
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]356
357<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
358<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
359Enable "FixIt" information in the diagnostics output.</dt>
360<dd>This option, which defaults to on, controls whether or not Clang prints the
361information on how to fix a specific diagnostic underneath it when it knows.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]362For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]363
364<pre>
365 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
366 #endif bad
367 ^
368 //
369</pre>
370
371<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
372the "//" line at the end of the message. This information is useful for users
373who may not understand what is wrong, but can be confusing for machine
374parsing.</p>
375</dd>
376
377<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]378<dt id="opt_fdiagnostics-print-source-range-info">
379<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]380Print machine parsable information about source ranges.</dt>
381<dd>This option, which defaults to off, controls whether or not Clang prints
382information about source ranges in a machine parsable format after the
383file/line/column number information. The information is a simple sequence of
384brace enclosed ranges, where each range lists the start and end line/column
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]385locations. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]386
387<pre>
388exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
389 P = (P-42) + Gamma*4;
390 ~~~~~~ ^ ~~~~~~~
391</pre>
392
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]393<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]394</dd>
395
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]396<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
397<dt id="opt_fdiagnostics-parseable-fixits">
398<b>-fdiagnostics-parseable-fixits</b>:
399Print Fix-Its in a machine parseable form.</dt>
400<dd><p>This option makes Clang print available Fix-Its in a machine parseable format at the end of diagnostics. The following example illustrates the format:</p>
401
402<pre>
Douglas Gregorbf5e09d2010-08-20 03:17:33 +0000[diff] [blame]403 fix-it:"t.cpp":{7:25-7:29}:"Gamma"
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]404</pre>
405
NAKAMURA Takumi44626362011-04-05 00:57:02 +0000[diff] [blame]406<p>The range printed is a half-open range, so in this example the characters at
407column 25 up to but not including column 29 on line 7 in t.cpp should be
408replaced with the string &quot;Gamma&quot;. Either the range or the replacement
409string may be empty (representing strict insertions and strict erasures,
410respectively). Both the file name and the insertion string escape backslash (as
411&quot;\\&quot;), tabs (as &quot;\t&quot;), newlines (as &quot;\n&quot;), double
412quotes(as &quot;\&quot;&quot;) and non-printable characters (as octal
413&quot;\xxx&quot;).</p>
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]414</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]415
416</dl>
417
418
419
420
421<!-- ===================================================== -->
422<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
423<!-- ===================================================== -->
424
425<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
426
427
428<dl>
429
430
431<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
432<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
433 the end of a preprocessor directive.</dt>
434<dd>This option, which defaults to on, enables warnings about extra tokens at
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]435the end of preprocessor directives. For example:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]436
437<pre>
438 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
439 #endif bad
440 ^
441</pre>
442
443<p>These extra tokens are not strictly conforming, and are usually best handled
444by commenting them out.</p>
445
446<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
447 and <a href="">-Wbaz</a>.</p>
448</dd>
449
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]450<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
451<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
452Warn about unqualified uses of a member template whose name resolves
453to another template at the location of the use.</dt>
454<dd>This option, which defaults to on, enables a warning in the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]455following code:
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]456
457<pre>
458template&lt;typename T> struct set{};
459template&lt;typename T> struct trait { typedef const T& type; };
460struct Value {
461 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
462};
463void foo() {
464 Value v;
465 v.set&lt;double>(3.2);
466}
467</pre>
468
469<p>C++ [basic.lookup.classref] requires this to be an error, but,
470because it's hard to work around, Clang downgrades it to a warning as
471an extension.</p>
472</dd>
473
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]474<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
475<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
476an unusable copy constructor when binding a reference to a temporary.</dt>
477<dd>This option, which defaults to on, enables warnings about binding a
478reference to a temporary when the temporary doesn't have a usable copy
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]479constructor. For example:
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]480
481<pre>
482 struct NonCopyable {
483 NonCopyable();
484 private:
485 NonCopyable(const NonCopyable&);
486 };
487 void foo(const NonCopyable&);
488 void bar() {
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]489 foo(NonCopyable()); // Disallowed in C++98; allowed in C++11.
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]490 }
491</pre>
492<pre>
493 struct NonCopyable2 {
494 NonCopyable2();
495 NonCopyable2(NonCopyable2&);
496 };
497 void foo(const NonCopyable2&);
498 void bar() {
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]499 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++11.
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]500 }
501</pre>
502
503<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
504argument whose instantiation produces a compile error, that error will
505still be a hard error in C++98 mode even if this warning is turned
506off.</p>
507
508</dd>
509
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]510</dl>
511
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]512<!-- ======================================================================= -->
513<h2 id="general_features">Language and Target-Independent Features</h2>
514<!-- ======================================================================= -->
515
516
517<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
518<h3 id="diagnostics">Controlling Errors and Warnings</h3>
519<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
520
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]521<p>Clang provides a number of ways to control which code constructs cause it to
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]522emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]523
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]524<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]525
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]526<p>When Clang emits a diagnostic, it includes rich information in the output,
527and gives you fine-grain control over which information is printed. Clang has
528the ability to print this information, and these are the options that control
529it:</p>
530
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]531<ol>
532<li>A file/line/column indicator that shows exactly where the diagnostic occurs
533 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
534 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
535<li>A categorization of the diagnostic as a note, warning, error, or fatal
536 error.</li>
537<li>A text string that describes what the problem is.</li>
538<li>An option that indicates how to control the diagnostic (for diagnostics that
539 support it) [<a
540 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]541<li>A <a href="#diagnostics_categories">high-level category</a> for the
542 diagnostic for clients that want to group diagnostics by class (for
543 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]544 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]545<li>The line of source code that the issue occurs on, along with a caret and
546 ranges that indicate the important locations [<a
547 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
548<li>"FixIt" information, which is a concise explanation of how to fix the
549 problem (when Clang is certain it knows) [<a
550 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
551<li>A machine-parsable representation of the ranges involved (off by
552 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]553 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]554</ol>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]555
556<p>For more information please see <a href="#cl_diag_formatting">Formatting of
557Diagnostics</a>.</p>
558
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]559
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]560<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]561
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]562<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]563
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]564<ul>
565<li>Ignored</li>
566<li>Note</li>
567<li>Warning</li>
568<li>Error</li>
569<li>Fatal</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]570</ul>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]571
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]572<h4 id="diagnostics_categories">Diagnostic Categories</h4>
573
574<p>Though not shown by default, diagnostics may each be associated with a
575 high-level category. This category is intended to make it possible to triage
576 builds that produce a large number of errors or warnings in a grouped way.
577</p>
578
579<p>Categories are not shown by default, but they can be turned on with the
580<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
581When set to "<tt>name</tt>", the category is printed textually in the diagnostic
582output. When it is set to "<tt>id</tt>", a category number is printed. The
583mapping of category names to category id's can be obtained by running '<tt>clang
584 --print-diagnostic-categories</tt>'.
585</p>
586
587<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
588 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]589
590<p>-W flags, -pedantic, etc</p>
591
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]592<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
593
594<p>Clang can also control what diagnostics are enabled through the use of
595pragmas in the source code. This is useful for turning off specific warnings
596in a section of source code. Clang supports GCC's pragma for compatibility
597with existing source code, as well as several extensions. </p>
598
599<p>The pragma may control any warning that can be used from the command line.
600Warnings may be set to ignored, warning, error, or fatal. The following
601example code will tell Clang or GCC to ignore the -Wall warnings:</p>
602
603<pre>
604#pragma GCC diagnostic ignored "-Wall"
605</pre>
606
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]607<p>In addition to all of the functionality provided by GCC's pragma, Clang
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]608also allows you to push and pop the current warning state. This is particularly
609useful when writing a header file that will be compiled by other people, because
610you don't know what warning flags they build with.</p>
611
612<p>In the below example
613-Wmultichar is ignored for only a single line of code, after which the
614diagnostics return to whatever state had previously existed.</p>
615
616<pre>
617#pragma clang diagnostic push
618#pragma clang diagnostic ignored "-Wmultichar"
619
620char b = 'df'; // no warning.
621
622#pragma clang diagnostic pop
623</pre>
624
625<p>The push and pop pragmas will save and restore the full diagnostic state of
626the compiler, regardless of how it was set. That means that it is possible to
627use push and pop around GCC compatible diagnostics and Clang will push and pop
628them appropriately, while GCC will ignore the pushes and pops as unknown
629pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
630GCC do not support the exact same set of warnings, so even when using GCC
631compatible #pragmas there is no guarantee that they will have identical behaviour
632on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]633
Ted Kremenekf391fa72011-08-18 01:17:05 +0000[diff] [blame]634<h4 id="diagnostics_enable_everything">Enabling All Warnings</h4>
635
636<p>In addition to the traditional <tt>-W</tt> flags, one can enable <b>all</b>
637 warnings by passing <tt>-Weverything</tt>.
638 This works as expected with <tt>-Werror</tt>,
639 and also includes the warnings from <tt>-pedantic</tt>.</p>
640
641<p>Note that when combined with <tt>-w</tt> (which disables all warnings), that
642 flag wins.</p>
643
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]644<h4 id="analyzer_diagnositics">Controlling Static Analyzer Diagnostics</h4>
645
646<p>While not strictly part of the compiler, the diagnostics from Clang's <a
647href="http://clang-analyzer.llvm.org">static analyzer</a> can also be influenced
648by the user via changes to the source code. This can be done in two ways:
649
650<ul>
651
652<li id="analyzer_annotations"><b>Annotations</b>: The static analyzer recognizes various GCC-style
653attributes (e.g., <tt>__attribute__((nonnull)))</tt>) that can either suppress
654static analyzer warnings or teach the analyzer about code invariants which
655enable it to find more bugs. While many of these attributes are standard GCC
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]656attributes, additional ones have been added to Clang to specifically support the
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]657static analyzer. Detailed information on these annotations can be found in the
658<a href="http://clang-analyzer.llvm.org/annotations.html">analyzer's
659documentation</a>.</li>
660
661<li><b><tt>__clang_analyzer__</tt></b>: When the static analyzer is using Clang
662to parse source files, it implicitly defines the preprocessor macro
663<tt>__clang_analyzer__</tt>. While discouraged, code can use this macro to
664selectively exclude code the analyzer examines. Here is an example:
665
666<pre>
667#ifndef __clang_analyzer__
668// Code not to be analyzed
669#endif
670</pre>
671
672In general, this usage is discouraged. Instead, we prefer that users file bugs
673against the analyzer when it flags false positives. There is also active
674discussion of allowing users in the future to selectively silence specific
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]675analyzer warnings (some of which can already be done using <a
Chris Lattner2c2a3852011-12-19 07:49:23 +0000[diff] [blame]676href="#analyzer_annotations">annotations</a>).</li>
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]677
678</ul>
679
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]680<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
681<h3 id="precompiledheaders">Precompiled Headers</h3>
682<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
683
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]684<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
685headers</a> are a general approach employed by many compilers to reduce
686compilation time. The underlying motivation of the approach is that it is
687common for the same (and often large) header files to be included by
688multiple source files. Consequently, compile times can often be greatly improved
689by caching some of the (redundant) work done by a compiler to process headers.
690Precompiled header files, which represent one of many ways to implement
691this optimization, are literally files that represent an on-disk cache that
692contains the vital information necessary to reduce some of the work
693needed to process a corresponding header file. While details of precompiled
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]694headers vary between compilers, precompiled headers have been shown to be
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]695highly effective at speeding up program compilation on systems with very large
696system headers (e.g., Mac OS/X).</p>
697
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]698<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]699
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]700<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]701the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
702interface in GCC for generating PCH files:</p>
703
704<pre>
705 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]706 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]707</pre>
708
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]709<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]710
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]711<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]712<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
713
714<pre>
715 $ clang -include test.h test.c -o test
716</pre>
717
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]718<p>The <tt>clang</tt> driver will first check if a PCH file for <tt>test.h</tt>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]719is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]720will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]721directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
722GCC.</p>
723
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]724<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]725for headers that are directly included within a source file. For example:</p>
726
727<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]728 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]729 $ cat test.c
730 #include "test.h"
731 $ clang test.c -o test
732</pre>
733
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]734<p>In this example, <tt>clang</tt> will not automatically use the PCH file for
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]735<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
736and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]737
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]738<h4>Relocatable PCH Files</h4>
739<p>It is sometimes necessary to build a precompiled header from headers that
740are not yet in their final, installed locations. For example, one might build a
741precompiled header within the build tree that is then meant to be installed
742alongside the headers. Clang permits the creation of "relocatable" precompiled
743headers, which are built with a given path (into the build directory) and can
744later be used from an installed location.</p>
745
746<p>To build a relocatable precompiled header, place your headers into a
747subdirectory whose structure mimics the installed location. For example, if you
748want to build a precompiled header for the header <code>mylib.h</code> that
749will be installed into <code>/usr/include</code>, create a subdirectory
750<code>build/usr/include</code> and place the header <code>mylib.h</code> into
751that subdirectory. If <code>mylib.h</code> depends on other headers, then
752they can be stored within <code>build/usr/include</code> in a way that mimics
753the installed location.</p>
754
755<p>Building a relocatable precompiled header requires two additional arguments.
756First, pass the <code>--relocatable-pch</code> flag to indicate that the
757resulting PCH file should be relocatable. Second, pass
758<code>-isysroot /path/to/build</code>, which makes all includes for your
759library relative to the build directory. For example:</p>
760
761<pre>
762 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
763</pre>
764
765<p>When loading the relocatable PCH file, the various headers used in the PCH
766file are found from the system header root. For example, <code>mylib.h</code>
767can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
768in some other system root, the <code>-isysroot</code> option can be used provide
769a different system root from which the headers will be based. For example,
770<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
771<code>mylib.h</code> in
772<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
773
774<p>Relocatable precompiled headers are intended to be used in a limited number
775of cases where the compilation environment is tightly controlled and the
776precompiled header cannot be generated after headers have been installed.
777Relocatable precompiled headers also have some performance impact, because
778the difference in location between the header locations at PCH build time vs.
779at the time of PCH use requires one of the PCH optimizations,
780<code>stat()</code> caching, to be disabled. However, this change is only
781likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]782
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]783<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
784<h3 id="codegen">Controlling Code Generation</h3>
785<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
786
787<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
788
789<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]790<dl>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]791<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
792on runtime code generation to check for undefined behavior.</dt>
793
794<dd>This option, which defaults to off, controls whether or not Clang
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]795adds runtime checks for undefined runtime behavior. If a check fails,
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]796<tt>__builtin_trap()</tt> is used to indicate failure.
797The checks are:
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]798<ul>
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]799<li>Subscripting where the static type of one operand is a variable
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]800 which is decayed from an array type and the other operand is
801 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]802<li>Shift operators where the amount shifted is greater or equal to the
803 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]804<li>If control flow reaches __builtin_unreachable.
805<li>When llvm implements more __builtin_object_size support, reads and
806 writes for objects that __builtin_object_size indicates we aren't
807 accessing valid memory. Bit-fields and vectors are not yet checked.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]808</ul>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]809</dd>
810
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]811<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
812Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]813<dd>This option tells the compiler to do not assume that C++'s global new
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]814operator will always return a pointer that does not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]815alias any other pointer when the function returns.</dd>
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]816
Evan Cheng4cf4b592011-04-08 22:34:21 +0000[diff] [blame]817<dt id="opt_ftrap-function"><b>-ftrap-function=[name]</b>: Instruct code
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]818generator to emit a function call to the specified function name for
819<tt>__builtin_trap()</tt>.</dt>
820
821<dd>LLVM code generator translates <tt>__builtin_trap()</tt> to a trap
822instruction if it is supported by the target ISA. Otherwise, the builtin is
823translated into a call to <tt>abort</tt>. If this option is set, then the code
824generator will always lower the builtin to a call to the specified function
825regardless of whether the target ISA has a trap instruction. This option is
Chris Lattner02e266b2011-04-08 22:58:43 +0000[diff] [blame]826useful for environments (e.g. deeply embedded) where a trap cannot be properly
827handled, or when some custom behavior is desired.</dd>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]828</dl>
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]829
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]830<!-- ======================================================================= -->
831<h2 id="c">C Language Features</h2>
832<!-- ======================================================================= -->
833
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]834<p>The support for standard C in clang is feature-complete except for the C99
835floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]836
837<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]838<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]839<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
840
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]841<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]842
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]843<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
844<h3 id="c_modes">Differences between various standard modes</h3>
845<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]846
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]847<p>clang supports the -std option, which changes what language mode clang uses.
848The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
849for those modes. If no -std option is specified, clang defaults to gnu99 mode.
850</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]851
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]852<p>Differences between all c* and gnu* modes:</p>
853<ul>
854<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]855<li>Target-specific defines not prefixed by underscores, like "linux", are
856defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]857<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
858-trigraphs option.</li>
859<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
860variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]861<li>The Apple "blocks" extension is recognized by default in gnu* modes
862on some platforms; it can be enabled in any mode with the "-fblocks"
863option.</li>
Chris Lattner741be6a2011-06-15 00:41:40 +0000[diff] [blame]864<li>Arrays that are VLA's according to the standard, but which can be constant
865 folded by the frontend are treated as fixed size arrays. This occurs for
866 things like "int X[(1, 2)];", which is technically a VLA. c* modes are
867 strictly compliant and treat these as VLAs.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]868</ul>
869
870<p>Differences between *89 and *99 modes:</p>
871<ul>
872<li>The *99 modes default to implementing "inline" as specified in C99, while
873the *89 modes implement the GNU version. This can be overridden for individual
874functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]875<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]876<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
877statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
878<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]879<li>"inline" is not recognized as a keyword in c89 mode.</li>
880<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]881<li>Commas are allowed in integer constant expressions in *99 modes.</li>
882<li>Arrays which are not lvalues are not implicitly promoted to pointers in
883*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]884<li>Some warnings are different.</li>
885</ul>
886
887<p>c94 mode is identical to c89 mode except that digraphs are enabled in
888c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
889
890<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
891<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
892<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
893
894<p>clang tries to be compatible with gcc as much as possible, but some gcc
895extensions are not implemented yet:</p>
896
897<ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]898
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]899<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]900(<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]901the uses described in the bug, this is likely to be implemented at some
902point, at least partially.</li>
903
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]904<li>clang does not support decimal floating point types (_Decimal32 and
905friends) or fixed-point types (_Fract and friends); nobody has expressed
906interest in these features yet, so it's hard to say when they will be
907implemented.</li>
908
909<li>clang does not support nested functions; this is a complex feature which
910is infrequently used, so it is unlikely to be implemented anytime soon.</li>
911
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]912<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]913to be implemented soon because it requires additional LLVM backend support.
914</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]915
916<li>clang does not support static initialization of flexible array
917members. This appears to be a rarely used extension, but could be
918implemented pending user demand.</li>
919
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]920<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
921This is used rarely, but in some potentially interesting places, like the
922glibc headers, so it may be implemented pending user demand. Note that
923because clang pretends to be like GCC 4.2, and this extension was introduced
924in 4.3, the glibc headers will not try to use this extension with clang at
925the moment.</li>
926
927<li>clang does not support the gcc extension for forward-declaring function
928parameters; this has not showed up in any real-world code yet, though, so it
929might never be implemented.</li>
930
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]931</ul>
932
933<p>This is not a complete list; if you find an unsupported extension
934missing from this list, please send an e-mail to cfe-dev. This list
935currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
936Also, this list does not include bugs in mostly-implemented features; please
937see the <a href="http://llvm.org/bugs/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer">
938bug tracker</a> for known existing bugs (FIXME: Is there a section for
939bug-reporting guidelines somewhere?).</p>
940
941<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
942<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
943<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
944
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]945<ul>
946
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]947<li>clang does not support the gcc extension that allows variable-length arrays
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]948in structures. This is for a few reasons: one, it is tricky
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]949to implement, two, the extension is completely undocumented, and three, the
Chris Lattnerb9d511c2010-10-28 02:20:32 +0000[diff] [blame]950extension appears to be rarely used. Note that clang <em>does</em> support
951flexible array members (arrays with a zero or unspecified size at the end of
952a structure).</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]953
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]954<li>clang does not have an equivalent to gcc's "fold"; this means that
955clang doesn't accept some constructs gcc might accept in contexts where a
Eli Friedman248f9732011-06-13 23:12:01 +0000[diff] [blame]956constant expression is required, like "x-x" where x is a variable.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]957
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]958<li>clang does not support __builtin_apply and friends; this extension is
959extremely obscure and difficult to implement reliably.</li>
960
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]961</ul>
962
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]963<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
964<h3 id="c_ms">Microsoft extensions</h3>
965<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
966
967<p>clang has some experimental support for extensions from
968Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]969option. This is the default for Windows targets. Note that the
970support is incomplete; enabling Microsoft extensions will silently drop
971certain constructs (including __declspec and Microsoft-style asm statements).
972</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]973
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]974<ul>
Douglas Gregord3b227d2010-12-14 16:21:49 +0000[diff] [blame]975<li>clang allows setting _MSC_VER with -fmsc-version=. It defaults to 1300 which
Michael J. Spencerdae4ac42010-10-21 05:21:48 +0000[diff] [blame]976is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
977what Windows SDK and c++stdlib headers clang can compile. This option will be
978removed when clang supports the full set of MS extensions required for these
979headers.</li>
980
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]981<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]982record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]983
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]984<li>clang supports the Microsoft "#pragma pack" feature for
985controlling record layout. GCC also contains support for this feature,
986however where MSVC and GCC are incompatible clang follows the MSVC
987definition.</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]988</ul>
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]989
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]990<!-- ======================================================================= -->
Richard Smithbdb10182011-11-21 20:54:59 +0000[diff] [blame]991<h2 id="cxx">C++ Language Features</h2>
992<!-- ======================================================================= -->
993
994<p>clang fully implements all of standard C++98 except for exported templates
995(which were removed in C++11), and
996<a href="http://clang.llvm.org/cxx_status.html">many C++11 features</a> are also
997implemented.</p>
998
999<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1000<h3 id="cxx_implimits">Controlling implementation limits</h3>
1001<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1002
1003<p><b>-fconstexpr-depth=N</b>: Sets the limit for recursive constexpr function
1004invocations to N. The default is 512.</p>
1005
1006<p><b>-ftemplate-depth=N</b>: Sets the limit for recursively nested template
1007instantiations to N. The default is 1024.</p>
1008
1009<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1010<h2 id="target_features">Target-Specific Features and Limitations</h2>
1011<!-- ======================================================================= -->
1012
1013
1014<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1015<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
1016<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1017
1018<!-- ======================== -->
1019<h4 id="target_arch_x86">X86</h4>
1020<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]1021
1022<p>The support for X86 (both 32-bit and 64-bit) is considered stable on Darwin
1023(Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to correctly
1024compile many large C, C++, Objective-C, and Objective-C++ codebases.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1025
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]1026<p>On x86_64-mingw32, passing i128(by value) is incompatible to Microsoft x64
1027calling conversion. You might need to tweak WinX86_64ABIInfo::classify()
1028in lib/CodeGen/TargetInfo.cpp.</p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1029
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1030<!-- ======================== -->
1031<h4 id="target_arch_arm">ARM</h4>
1032<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]1033
1034<p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable on
1035Darwin (iOS): it has been tested to correctly compile many large C, C++,
Bob Wilson4ea8dfa2011-01-10 17:55:14 +0000[diff] [blame]1036Objective-C, and Objective-C++ codebases. Clang only supports a limited number
1037of ARM architectures. It does not yet fully support ARMv5, for example.</p>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1038
1039<!-- ======================== -->
1040<h4 id="target_arch_other">Other platforms</h4>
1041<!-- ======================== -->
1042clang currently contains some support for PPC and Sparc; however, significant
1043pieces of code generation are still missing, and they haven't undergone
1044significant testing.
1045
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1046<p>clang contains limited support for the MSP430 embedded processor, but both
1047the clang support and the LLVM backend support are highly experimental.
1048
1049<p>Other platforms are completely unsupported at the moment. Adding the
1050minimal support needed for parsing and semantic analysis on a new platform
1051is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
1052of support is also sufficient for conversion to LLVM IR for simple programs.
1053Proper support for conversion to LLVM IR requires adding code to
1054lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
1055Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1056
1057<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1058<h3 id="target_os">Operating System Features and Limitations</h3>
1059<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1060
1061<!-- ======================================= -->
1062<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
1063<!-- ======================================= -->
1064
1065<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
1066
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1067<!-- ======================================= -->
1068<h4 id="target_os_win32">Windows</h4>
1069<!-- ======================================= -->
1070
1071<p>Experimental supports are on Cygming.</p>
1072
1073<h5>Cygwin</h5>
1074
1075<p>Clang works on Cygwin-1.7.</p>
1076
1077<h5>MinGW32</h5>
1078
1079<p>Clang works on some mingw32 distributions.
1080Clang assumes directories as below;</p>
1081
1082<ul>
1083<li><tt>C:/mingw/include</tt></li>
1084<li><tt>C:/mingw/lib</tt></li>
1085<li><tt>C:/mingw/lib/gcc/mingw32/4.[3-5].0/include/c++</tt></li>
1086</ul>
1087
NAKAMURA Takumi0e53df62011-11-17 07:54:13 +0000[diff] [blame]1088<p>On MSYS, a few tests might fail.</p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1089
1090<h5>MinGW-w64</h5>
1091
Douglas Gregordad879a2011-08-30 00:40:12 +0000[diff] [blame]1092<p>For 32-bit (i686-w64-mingw32), and 64-bit (x86_64-w64-mingw32), Clang assumes as below;<p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1093
1094<ul>
Douglas Gregordad879a2011-08-30 00:40:12 +0000[diff] [blame]1095<li><tt>GCC versions 4.5.0 to 4.5.3, 4.6.0 to 4.6.2, or 4.7.0 (for the C++ header search path)</tt></li>
1096<li><tt>some_directory/bin/gcc.exe</tt></li>
1097<li><tt>some_directory/bin/clang.exe</tt></li>
1098<li><tt>some_directory/bin/clang++.exe</tt></li>
1099<li><tt>some_directory/bin/../include/c++/GCC_version</tt></li>
1100<li><tt>some_directory/bin/../include/c++/GCC_version/x86_64-w64-mingw32</tt></li>
1101<li><tt>some_directory/bin/../include/c++/GCC_version/i686-w64-mingw32</tt></li>
1102<li><tt>some_directory/bin/../include/c++/GCC_version/backward</tt></li>
1103<li><tt>some_directory/bin/../x86_64-w64-mingw32/include</tt></li>
1104<li><tt>some_directory/bin/../i686-w64-mingw32/include</tt></li>
1105<li><tt>some_directory/bin/../include</tt></li>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1106</ul>
1107
Douglas Gregordad879a2011-08-30 00:40:12 +0000[diff] [blame]1108<p>This directory layout is standard for any toolchain you will find on the official <a href="mingw-w64.sourceforge.net">MinGW-w64 website</a>.
1109
1110<p>Clang expects the GCC executable &quot;gcc.exe&quot; compiled for i686-w64-mingw32 (or x86_64-w64-mingw32) to be present on PATH.</p>
1111
1112<p><a href="http://llvm.org/bugs/show_bug.cgi?id=9072">Some tests might fail</a>
1113on x86_64-w64-mingw32.</p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1114
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1115</div>
1116</body>
1117</html>