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16<div id="content">
17
18<h1>Clang Compiler User's Manual</h1>
19
20<ul>
21<li><a href="#intro">Introduction</a>
22 <ul>
23 <li><a href="#terminology">Terminology</a></li>
24 <li><a href="#basicusage">Basic Usage</a></li>
25 </ul>
26</li>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]27<li><a href="#commandline">Command Line Options</a>
28 <ul>
29 <li><a href="#cl_diagnostics">Options to Control Error and Warning
30 Messages</a></li>
31 </ul>
32</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]33<li><a href="#general_features">Language and Target-Independent Features</a>
34 <ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]35 <li><a href="#diagnostics">Controlling Errors and Warnings</a>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]36 <ul>
37 <li><a href="#diagnostics_display">Controlling How Clang Displays Diagnostics</a></li>
38 <li><a href="#diagnostics_mappings">Diagnostic Mappings</a></li>
Chris Lattner67db8cd2010-05-30 23:42:51 +0000[diff] [blame]39 <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]40 <li><a href="#diagnostics_commandline">Controlling Diagnostics via Command Line Flags</a></li>
41 <li><a href="#diagnostics_pragmas">Controlling Diagnostics via Pragmas</a></li>
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]42 <li><a href="#analyzer_diagnositics">Controlling Static Analyzer Diagnostics</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]43 </ul>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]44 </li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]45 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]46 <li><a href="#codegen">Controlling Code Generation</a></li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]47 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]48</li>
49<li><a href="#c">C Language Features</a>
50 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]51 <li><a href="#c_ext">Extensions supported by clang</a></li>
52 <li><a href="#c_modes">Differences between various standard modes</a></li>
53 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
54 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
55 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]56 </ul>
57</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]58<li><a href="#target_features">Target-Specific Features and Limitations</a>
59 <ul>
60 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
61 <ul>
62 <li><a href="#target_arch_x86">X86</a></li>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]63 <li><a href="#target_arch_arm">ARM</a></li>
64 <li><a href="#target_arch_other">Other platforms</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]65 </ul>
66 </li>
67 <li><a href="#target_os">Operating System Features and Limitations</a>
68 <ul>
69 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
70 <li>Linux, etc.</li>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]71 <li><a href="#target_os_win32">Windows</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]72 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]73 </li>
74 </ul>
75</li>
76</ul>
77
78
79<!-- ======================================================================= -->
80<h2 id="intro">Introduction</h2>
81<!-- ======================================================================= -->
82
83<p>The Clang Compiler is an open-source compiler for the C family of programming
84languages, aiming to be the best in class implementation of these languages.
85Clang builds on the LLVM optimizer and code generator, allowing it to provide
86high-quality optimization and code generation support for many targets. For
87more general information, please see the <a href="http://clang.llvm.org">Clang
88Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
89
90<p>This document describes important notes about using Clang as a compiler for
91an end-user, documenting the supported features, command line options, etc. If
92you are interested in using Clang to build a tool that processes code, please
93see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
94interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
95Static Analyzer</a>, please see its web page.</p>
96
97<p>Clang is designed to support the C family of programming languages, which
98includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
99href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
100dialects of those. For language-specific information, please see the
101corresponding language specific section:</p>
102
103<ul>
104<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
105 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
106<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
107 variants depending on base language.</li>
108<li><a href="#cxx">C++ Language Features</a></li>
109<li><a href="#objcxx">Objective C++ Language</a></li>
110</ul>
111
112<p>In addition to these base languages and their dialects, Clang supports a
113broad variety of language extensions, which are documented in the corresponding
114language section. These extensions are provided to be compatible with the GCC,
115Microsoft, and other popular compilers as well as to improve functionality
116through Clang-specific features. The Clang driver and language features are
117intentionally designed to be as compatible with the GNU GCC compiler as
118reasonably possible, easing migration from GCC to Clang. In most cases, code
119"just works".</p>
120
121<p>In addition to language specific features, Clang has a variety of features
122that depend on what CPU architecture or operating system is being compiled for.
Douglas Gregorcd5a5052009-11-09 15:15:41 +0000[diff] [blame]123Please see the <a href="#target_features">Target-Specific Features and
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]124Limitations</a> section for more details.</p>
125
126<p>The rest of the introduction introduces some basic <a
127href="#terminology">compiler terminology</a> that is used throughout this manual
128and contains a basic <a href="#basicusage">introduction to using Clang</a>
129as a command line compiler.</p>
130
131<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
132<h3 id="terminology">Terminology</h3>
133<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
134
135<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
136 optimizer</p>
137
138<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
139<h3 id="basicusage">Basic Usage</h3>
140<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
141
142<p>Intro to how to use a C compiler for newbies.</p>
143<p>
144compile + link
145
146compile then link
147
148debug info
149
150enabling optimizations
151
152picking a language to use, defaults to C99 by default. Autosenses based on
153extension.
154
155using a makefile
156</p>
157
158
159<!-- ======================================================================= -->
160<h2 id="commandline">Command Line Options</h2>
161<!-- ======================================================================= -->
162
163<p>
164This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]165depth on the ones that are covered by other sections. However, the first part
166introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]167</p>
168
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]169
170<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
171<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
172<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
173
174<p><b>-Werror</b>: Turn warnings into errors.</p>
175<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
176<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
177 specified.</p>
178<p><b>-Wfoo</b>: Enable warning foo</p>
179<p><b>-Wno-foo</b>: Disable warning foo</p>
180<p><b>-w</b>: Disable all warnings.</p>
181<p><b>-pedantic</b>: Warn on language extensions.</p>
182<p><b>-pedantic-errors</b>: Error on language extensions.</p>
183<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
184
Chris Lattner0f0c9632010-04-07 20:49:23 +0000[diff] [blame]185<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
186 been produced. The default is 20, and the error limit can be disabled with
187 -ferror-limit=0.</p>
188
Douglas Gregor575cf372010-04-20 07:18:24 +0000[diff] [blame]189<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>
190
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]191<!-- ================================================= -->
192<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
193<!-- ================================================= -->
194
195<p>Clang aims to produce beautiful diagnostics by default, particularly for new
196users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]197preferences, and sometimes Clang is driven by another program that wants to
198parse simple and consistent output, not a person. For these cases, Clang
199provides a wide range of options to control the exact output format of the
200diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]201
202<dl>
203
204<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
205<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
206diagnostic.</dt>
207<dd>This option, which defaults to on, controls whether or not Clang prints the
208column number of a diagnostic. For example, when this is enabled, Clang will
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]209print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]210
211<pre>
212 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
213 #endif bad
214 ^
215 //
216</pre>
217
218<p>When this is disabled, Clang will print "test.c:28: warning..." with no
219column number.</p>
220</dd>
221
222<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
223<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
224source file/line/column information in diagnostic.</dt>
225<dd>This option, which defaults to on, controls whether or not Clang prints the
226filename, line number and column number of a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]227when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]228
229<pre>
230 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
231 #endif bad
232 ^
233 //
234</pre>
235
236<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
237</dd>
238
239<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
240<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
241line and ranges from source code in diagnostic.</dt>
242<dd>This option, which defaults to on, controls whether or not Clang prints the
243source line, source ranges, and caret when emitting a diagnostic. For example,
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]244when this is enabled, Clang will print something like:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]245
246<pre>
247 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
248 #endif bad
249 ^
250 //
251</pre>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]252</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]253<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]254<dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
255<dd>This option, which defaults to on when a color-capable terminal is
256 detected, controls whether or not Clang prints diagnostics in color.
257 When this option is enabled, Clang will use colors to highlight
258 specific parts of the diagnostic, e.g.,
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]259 <pre>
260 <b><font color="black">test.c:28:8: <font color="magenta">warning</font>: extra tokens at end of #endif directive [-Wextra-tokens]</font></b>
261 #endif bad
262 <font color="green">^</font>
263 <font color="green">//</font>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]264</pre>
Chris Lattner4e1c53d2011-01-24 03:47:34 +0000[diff] [blame]265
266<p>When this is disabled, Clang will just print:</p>
267
268<pre>
269 test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
270 #endif bad
271 ^
272 //
273</pre>
274</dd>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame]275<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregorc9471b02011-05-21 17:07:29 +0000[diff] [blame]276<dt id="opt_fdiagnostics-format"><b>-fdiagnostics-format=clang/msvc/vi</b>:
277Changes diagnostic output format to better match IDEs and command line tools.</dt>
278<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:
279
280 <dl>
281 <dt><b>clang</b> (default)</dt>
282 <dd>
283 <pre>t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
284 </dd>
285
286 <dt><b>msvc</b></dt>
287 <dd>
288 <pre>t.c(3,11) : warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
289 </dd>
290
291 <dt><b>vi</b></dt>
292 <dd>
293 <pre>t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
294 </dd>
295 </dl>
296</dd>
297
298<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Argyrios Kyrtzidis477aab62011-05-25 05:05:01 +0000[diff] [blame]299<dt id="opt_fdiagnostics-show-name"><b>-f[no-]diagnostics-show-name</b>:
300Enable the display of the diagnostic name.</dt>
301<dd>This option, which defaults to off, controls whether or not
302Clang prints the associated name.</dd>
303<br>
304<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]305<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
306Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
307<dd>This option, which defaults to on,
308controls whether or not Clang prints the associated <A
309href="#cl_diag_warning_groups">warning group</a> option name when outputting
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]310a warning diagnostic. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]311
312<pre>
313 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
314 #endif bad
315 ^
316 //
317</pre>
318
319<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
320the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
321diagnostic. This information tells you the flag needed to enable or disable the
322diagnostic, either from the command line or through <a
323href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
324
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]325<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
326<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
327Enable printing category information in diagnostic line.</dt>
328<dd>This option, which defaults to "none",
329controls whether or not Clang prints the category associated with a diagnostic
330when emitting it. Each diagnostic may or many not have an associated category,
331if it has one, it is listed in the diagnostic categorization field of the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]332diagnostic line (in the []'s).
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]333
334<p>For example, a format string warning will produce these three renditions
335based on the setting of this option:</p>
336
337<pre>
338 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
339 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
340 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
341</pre>
342
343<p>This category can be used by clients that want to group diagnostics by
344category, so it should be a high level category. We want dozens of these, not
345hundreds or thousands of them.</p>
346</dd>
347
348
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]349
350<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
351<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
352Enable "FixIt" information in the diagnostics output.</dt>
353<dd>This option, which defaults to on, controls whether or not Clang prints the
354information on how to fix a specific diagnostic underneath it when it knows.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]355For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]356
357<pre>
358 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
359 #endif bad
360 ^
361 //
362</pre>
363
364<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
365the "//" line at the end of the message. This information is useful for users
366who may not understand what is wrong, but can be confusing for machine
367parsing.</p>
368</dd>
369
370<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]371<dt id="opt_fdiagnostics-print-source-range-info">
372<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]373Print machine parsable information about source ranges.</dt>
374<dd>This option, which defaults to off, controls whether or not Clang prints
375information about source ranges in a machine parsable format after the
376file/line/column number information. The information is a simple sequence of
377brace enclosed ranges, where each range lists the start and end line/column
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]378locations. For example, in this output:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]379
380<pre>
381exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
382 P = (P-42) + Gamma*4;
383 ~~~~~~ ^ ~~~~~~~
384</pre>
385
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]386<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]387</dd>
388
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]389<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
390<dt id="opt_fdiagnostics-parseable-fixits">
391<b>-fdiagnostics-parseable-fixits</b>:
392Print Fix-Its in a machine parseable form.</dt>
393<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>
394
395<pre>
Douglas Gregorbf5e09d2010-08-20 03:17:33 +0000[diff] [blame]396 fix-it:"t.cpp":{7:25-7:29}:"Gamma"
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]397</pre>
398
NAKAMURA Takumi44626362011-04-05 00:57:02 +0000[diff] [blame]399<p>The range printed is a half-open range, so in this example the characters at
400column 25 up to but not including column 29 on line 7 in t.cpp should be
401replaced with the string &quot;Gamma&quot;. Either the range or the replacement
402string may be empty (representing strict insertions and strict erasures,
403respectively). Both the file name and the insertion string escape backslash (as
404&quot;\\&quot;), tabs (as &quot;\t&quot;), newlines (as &quot;\n&quot;), double
405quotes(as &quot;\&quot;&quot;) and non-printable characters (as octal
406&quot;\xxx&quot;).</p>
Douglas Gregor4786c152010-08-19 20:24:43 +0000[diff] [blame]407</dd>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]408
409</dl>
410
411
412
413
414<!-- ===================================================== -->
415<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
416<!-- ===================================================== -->
417
418<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
419
420
421<dl>
422
423
424<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
425<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
426 the end of a preprocessor directive.</dt>
427<dd>This option, which defaults to on, enables warnings about extra tokens at
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]428the end of preprocessor directives. For example:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]429
430<pre>
431 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
432 #endif bad
433 ^
434</pre>
435
436<p>These extra tokens are not strictly conforming, and are usually best handled
437by commenting them out.</p>
438
439<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
440 and <a href="">-Wbaz</a>.</p>
441</dd>
442
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]443<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
444<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
445Warn about unqualified uses of a member template whose name resolves
446to another template at the location of the use.</dt>
447<dd>This option, which defaults to on, enables a warning in the
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]448following code:
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]449
450<pre>
451template&lt;typename T> struct set{};
452template&lt;typename T> struct trait { typedef const T& type; };
453struct Value {
454 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
455};
456void foo() {
457 Value v;
458 v.set&lt;double>(3.2);
459}
460</pre>
461
462<p>C++ [basic.lookup.classref] requires this to be an error, but,
463because it's hard to work around, Clang downgrades it to a warning as
464an extension.</p>
465</dd>
466
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]467<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
468<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
469an unusable copy constructor when binding a reference to a temporary.</dt>
470<dd>This option, which defaults to on, enables warnings about binding a
471reference to a temporary when the temporary doesn't have a usable copy
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]472constructor. For example:
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]473
474<pre>
475 struct NonCopyable {
476 NonCopyable();
477 private:
478 NonCopyable(const NonCopyable&);
479 };
480 void foo(const NonCopyable&);
481 void bar() {
482 foo(NonCopyable()); // Disallowed in C++98; allowed in C++0x.
483 }
484</pre>
485<pre>
486 struct NonCopyable2 {
487 NonCopyable2();
488 NonCopyable2(NonCopyable2&);
489 };
490 void foo(const NonCopyable2&);
491 void bar() {
492 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++0x.
493 }
494</pre>
495
496<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
497argument whose instantiation produces a compile error, that error will
498still be a hard error in C++98 mode even if this warning is turned
499off.</p>
500
501</dd>
502
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]503</dl>
504
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]505<!-- ======================================================================= -->
506<h2 id="general_features">Language and Target-Independent Features</h2>
507<!-- ======================================================================= -->
508
509
510<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
511<h3 id="diagnostics">Controlling Errors and Warnings</h3>
512<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
513
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]514<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]515emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]516
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]517<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]518
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]519<p>When Clang emits a diagnostic, it includes rich information in the output,
520and gives you fine-grain control over which information is printed. Clang has
521the ability to print this information, and these are the options that control
522it:</p>
523
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]524<ol>
525<li>A file/line/column indicator that shows exactly where the diagnostic occurs
526 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
527 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
528<li>A categorization of the diagnostic as a note, warning, error, or fatal
529 error.</li>
530<li>A text string that describes what the problem is.</li>
Argyrios Kyrtzidis477aab62011-05-25 05:05:01 +0000[diff] [blame]531<li>An option that indicates whether to print the diagnostic name [<a
532 href="#opt_fdiagnostics-show-name">-fdiagnostics-show-name</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]533<li>An option that indicates how to control the diagnostic (for diagnostics that
534 support it) [<a
535 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]536<li>A <a href="#diagnostics_categories">high-level category</a> for the
537 diagnostic for clients that want to group diagnostics by class (for
538 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]539 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]540<li>The line of source code that the issue occurs on, along with a caret and
541 ranges that indicate the important locations [<a
542 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
543<li>"FixIt" information, which is a concise explanation of how to fix the
544 problem (when Clang is certain it knows) [<a
545 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
546<li>A machine-parsable representation of the ranges involved (off by
547 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]548 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]549</ol>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]550
551<p>For more information please see <a href="#cl_diag_formatting">Formatting of
552Diagnostics</a>.</p>
553
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]554
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]555<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]556
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]557<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]558
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]559<ul>
560<li>Ignored</li>
561<li>Note</li>
562<li>Warning</li>
563<li>Error</li>
564<li>Fatal</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]565</ul>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]566
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]567<h4 id="diagnostics_categories">Diagnostic Categories</h4>
568
569<p>Though not shown by default, diagnostics may each be associated with a
570 high-level category. This category is intended to make it possible to triage
571 builds that produce a large number of errors or warnings in a grouped way.
572</p>
573
574<p>Categories are not shown by default, but they can be turned on with the
575<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
576When set to "<tt>name</tt>", the category is printed textually in the diagnostic
577output. When it is set to "<tt>id</tt>", a category number is printed. The
578mapping of category names to category id's can be obtained by running '<tt>clang
579 --print-diagnostic-categories</tt>'.
580</p>
581
582<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
583 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]584
585<p>-W flags, -pedantic, etc</p>
586
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]587<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
588
589<p>Clang can also control what diagnostics are enabled through the use of
590pragmas in the source code. This is useful for turning off specific warnings
591in a section of source code. Clang supports GCC's pragma for compatibility
592with existing source code, as well as several extensions. </p>
593
594<p>The pragma may control any warning that can be used from the command line.
595Warnings may be set to ignored, warning, error, or fatal. The following
596example code will tell Clang or GCC to ignore the -Wall warnings:</p>
597
598<pre>
599#pragma GCC diagnostic ignored "-Wall"
600</pre>
601
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]602<p>In addition to all of the functionality provided by GCC's pragma, Clang
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]603also allows you to push and pop the current warning state. This is particularly
604useful when writing a header file that will be compiled by other people, because
605you don't know what warning flags they build with.</p>
606
607<p>In the below example
608-Wmultichar is ignored for only a single line of code, after which the
609diagnostics return to whatever state had previously existed.</p>
610
611<pre>
612#pragma clang diagnostic push
613#pragma clang diagnostic ignored "-Wmultichar"
614
615char b = 'df'; // no warning.
616
617#pragma clang diagnostic pop
618</pre>
619
620<p>The push and pop pragmas will save and restore the full diagnostic state of
621the compiler, regardless of how it was set. That means that it is possible to
622use push and pop around GCC compatible diagnostics and Clang will push and pop
623them appropriately, while GCC will ignore the pushes and pops as unknown
624pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
625GCC do not support the exact same set of warnings, so even when using GCC
626compatible #pragmas there is no guarantee that they will have identical behaviour
627on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]628
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]629<h4 id="analyzer_diagnositics">Controlling Static Analyzer Diagnostics</h4>
630
631<p>While not strictly part of the compiler, the diagnostics from Clang's <a
632href="http://clang-analyzer.llvm.org">static analyzer</a> can also be influenced
633by the user via changes to the source code. This can be done in two ways:
634
635<ul>
636
637<li id="analyzer_annotations"><b>Annotations</b>: The static analyzer recognizes various GCC-style
638attributes (e.g., <tt>__attribute__((nonnull)))</tt>) that can either suppress
639static analyzer warnings or teach the analyzer about code invariants which
640enable it to find more bugs. While many of these attributes are standard GCC
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]641attributes, additional ones have been added to Clang to specifically support the
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]642static analyzer. Detailed information on these annotations can be found in the
643<a href="http://clang-analyzer.llvm.org/annotations.html">analyzer's
644documentation</a>.</li>
645
646<li><b><tt>__clang_analyzer__</tt></b>: When the static analyzer is using Clang
647to parse source files, it implicitly defines the preprocessor macro
648<tt>__clang_analyzer__</tt>. While discouraged, code can use this macro to
649selectively exclude code the analyzer examines. Here is an example:
650
651<pre>
652#ifndef __clang_analyzer__
653// Code not to be analyzed
654#endif
655</pre>
656
657In general, this usage is discouraged. Instead, we prefer that users file bugs
658against the analyzer when it flags false positives. There is also active
659discussion of allowing users in the future to selectively silence specific
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]660analyzer warnings (some of which can already be done using <a
Ted Kremenek2fb11eb2010-08-24 18:12:35 +0000[diff] [blame]661href="analyzer_annotations">annotations</a>).</li>
662
663</ul>
664
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]665<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
666<h3 id="precompiledheaders">Precompiled Headers</h3>
667<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
668
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]669<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
670headers</a> are a general approach employed by many compilers to reduce
671compilation time. The underlying motivation of the approach is that it is
672common for the same (and often large) header files to be included by
673multiple source files. Consequently, compile times can often be greatly improved
674by caching some of the (redundant) work done by a compiler to process headers.
675Precompiled header files, which represent one of many ways to implement
676this optimization, are literally files that represent an on-disk cache that
677contains the vital information necessary to reduce some of the work
678needed to process a corresponding header file. While details of precompiled
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]679headers vary between compilers, precompiled headers have been shown to be
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]680highly effective at speeding up program compilation on systems with very large
681system headers (e.g., Mac OS/X).</p>
682
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]683<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]684
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]685<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]686the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
687interface in GCC for generating PCH files:</p>
688
689<pre>
690 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]691 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]692</pre>
693
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]694<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]695
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]696<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]697<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
698
699<pre>
700 $ clang -include test.h test.c -o test
701</pre>
702
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]703<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]704is 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]705will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]706directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
707GCC.</p>
708
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]709<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]710for headers that are directly included within a source file. For example:</p>
711
712<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]713 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]714 $ cat test.c
715 #include "test.h"
716 $ clang test.c -o test
717</pre>
718
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]719<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]720<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
721and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]722
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]723<h4>Relocatable PCH Files</h4>
724<p>It is sometimes necessary to build a precompiled header from headers that
725are not yet in their final, installed locations. For example, one might build a
726precompiled header within the build tree that is then meant to be installed
727alongside the headers. Clang permits the creation of "relocatable" precompiled
728headers, which are built with a given path (into the build directory) and can
729later be used from an installed location.</p>
730
731<p>To build a relocatable precompiled header, place your headers into a
732subdirectory whose structure mimics the installed location. For example, if you
733want to build a precompiled header for the header <code>mylib.h</code> that
734will be installed into <code>/usr/include</code>, create a subdirectory
735<code>build/usr/include</code> and place the header <code>mylib.h</code> into
736that subdirectory. If <code>mylib.h</code> depends on other headers, then
737they can be stored within <code>build/usr/include</code> in a way that mimics
738the installed location.</p>
739
740<p>Building a relocatable precompiled header requires two additional arguments.
741First, pass the <code>--relocatable-pch</code> flag to indicate that the
742resulting PCH file should be relocatable. Second, pass
743<code>-isysroot /path/to/build</code>, which makes all includes for your
744library relative to the build directory. For example:</p>
745
746<pre>
747 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
748</pre>
749
750<p>When loading the relocatable PCH file, the various headers used in the PCH
751file are found from the system header root. For example, <code>mylib.h</code>
752can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
753in some other system root, the <code>-isysroot</code> option can be used provide
754a different system root from which the headers will be based. For example,
755<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
756<code>mylib.h</code> in
757<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
758
759<p>Relocatable precompiled headers are intended to be used in a limited number
760of cases where the compilation environment is tightly controlled and the
761precompiled header cannot be generated after headers have been installed.
762Relocatable precompiled headers also have some performance impact, because
763the difference in location between the header locations at PCH build time vs.
764at the time of PCH use requires one of the PCH optimizations,
765<code>stat()</code> caching, to be disabled. However, this change is only
766likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]767
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]768<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
769<h3 id="codegen">Controlling Code Generation</h3>
770<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
771
772<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
773
774<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]775<dl>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]776<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
777on runtime code generation to check for undefined behavior.</dt>
778
779<dd>This option, which defaults to off, controls whether or not Clang
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]780adds runtime checks for undefined runtime behavior. If a check fails,
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]781<tt>__builtin_trap()</tt> is used to indicate failure.
782The checks are:
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]783<ul>
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]784<li>Subscripting where the static type of one operand is a variable
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]785 which is decayed from an array type and the other operand is
786 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]787<li>Shift operators where the amount shifted is greater or equal to the
788 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]789<li>If control flow reaches __builtin_unreachable.
790<li>When llvm implements more __builtin_object_size support, reads and
791 writes for objects that __builtin_object_size indicates we aren't
792 accessing valid memory. Bit-fields and vectors are not yet checked.
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]793</ul>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]794</dd>
795
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]796<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
797Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]798<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]799operator will always return a pointer that does not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]800alias any other pointer when the function returns.</dd>
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]801
Evan Cheng4cf4b592011-04-08 22:34:21 +0000[diff] [blame]802<dt id="opt_ftrap-function"><b>-ftrap-function=[name]</b>: Instruct code
Evan Chengfda026b2011-04-08 22:18:01 +0000[diff] [blame]803generator to emit a function call to the specified function name for
804<tt>__builtin_trap()</tt>.</dt>
805
806<dd>LLVM code generator translates <tt>__builtin_trap()</tt> to a trap
807instruction if it is supported by the target ISA. Otherwise, the builtin is
808translated into a call to <tt>abort</tt>. If this option is set, then the code
809generator will always lower the builtin to a call to the specified function
810regardless of whether the target ISA has a trap instruction. This option is
Chris Lattner02e266b2011-04-08 22:58:43 +0000[diff] [blame]811useful for environments (e.g. deeply embedded) where a trap cannot be properly
812handled, or when some custom behavior is desired.</dd>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]813</dl>
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]814
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]815<!-- ======================================================================= -->
816<h2 id="c">C Language Features</h2>
817<!-- ======================================================================= -->
818
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]819<p>The support for standard C in clang is feature-complete except for the C99
820floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]821
822<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]823<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]824<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
825
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]826<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]827
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]828<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
829<h3 id="c_modes">Differences between various standard modes</h3>
830<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]831
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]832<p>clang supports the -std option, which changes what language mode clang uses.
833The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
834for those modes. If no -std option is specified, clang defaults to gnu99 mode.
835</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]836
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]837<p>Differences between all c* and gnu* modes:</p>
838<ul>
839<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]840<li>Target-specific defines not prefixed by underscores, like "linux", are
841defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]842<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
843-trigraphs option.</li>
844<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
845variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]846<li>The Apple "blocks" extension is recognized by default in gnu* modes
847on some platforms; it can be enabled in any mode with the "-fblocks"
848option.</li>
Chris Lattner741be6a2011-06-15 00:41:40 +0000[diff] [blame]849<li>Arrays that are VLA's according to the standard, but which can be constant
850 folded by the frontend are treated as fixed size arrays. This occurs for
851 things like "int X[(1, 2)];", which is technically a VLA. c* modes are
852 strictly compliant and treat these as VLAs.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]853</ul>
854
855<p>Differences between *89 and *99 modes:</p>
856<ul>
857<li>The *99 modes default to implementing "inline" as specified in C99, while
858the *89 modes implement the GNU version. This can be overridden for individual
859functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]860<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]861<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
862statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
863<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]864<li>"inline" is not recognized as a keyword in c89 mode.</li>
865<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]866<li>Commas are allowed in integer constant expressions in *99 modes.</li>
867<li>Arrays which are not lvalues are not implicitly promoted to pointers in
868*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]869<li>Some warnings are different.</li>
870</ul>
871
872<p>c94 mode is identical to c89 mode except that digraphs are enabled in
873c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
874
875<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
876<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
877<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
878
879<p>clang tries to be compatible with gcc as much as possible, but some gcc
880extensions are not implemented yet:</p>
881
882<ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]883
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]884<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]885(<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]886the uses described in the bug, this is likely to be implemented at some
887point, at least partially.</li>
888
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]889<li>clang does not support decimal floating point types (_Decimal32 and
890friends) or fixed-point types (_Fract and friends); nobody has expressed
891interest in these features yet, so it's hard to say when they will be
892implemented.</li>
893
894<li>clang does not support nested functions; this is a complex feature which
895is infrequently used, so it is unlikely to be implemented anytime soon.</li>
896
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]897<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]898to be implemented soon because it requires additional LLVM backend support.
899</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]900
901<li>clang does not support static initialization of flexible array
902members. This appears to be a rarely used extension, but could be
903implemented pending user demand.</li>
904
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]905<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
906This is used rarely, but in some potentially interesting places, like the
907glibc headers, so it may be implemented pending user demand. Note that
908because clang pretends to be like GCC 4.2, and this extension was introduced
909in 4.3, the glibc headers will not try to use this extension with clang at
910the moment.</li>
911
912<li>clang does not support the gcc extension for forward-declaring function
913parameters; this has not showed up in any real-world code yet, though, so it
914might never be implemented.</li>
915
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]916</ul>
917
918<p>This is not a complete list; if you find an unsupported extension
919missing from this list, please send an e-mail to cfe-dev. This list
920currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
921Also, this list does not include bugs in mostly-implemented features; please
922see 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">
923bug tracker</a> for known existing bugs (FIXME: Is there a section for
924bug-reporting guidelines somewhere?).</p>
925
926<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
927<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
928<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
929
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]930<ul>
931
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]932<li>clang does not support the gcc extension that allows variable-length arrays
Chris Lattnerd462b6a2011-01-24 03:47:59 +0000[diff] [blame]933in structures. This is for a few reasons: one, it is tricky
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]934to implement, two, the extension is completely undocumented, and three, the
Chris Lattnerb9d511c2010-10-28 02:20:32 +0000[diff] [blame]935extension appears to be rarely used. Note that clang <em>does</em> support
936flexible array members (arrays with a zero or unspecified size at the end of
937a structure).</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]938
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]939<li>clang does not have an equivalent to gcc's "fold"; this means that
940clang doesn't accept some constructs gcc might accept in contexts where a
Eli Friedman248f9732011-06-13 23:12:01 +0000[diff] [blame]941constant expression is required, like "x-x" where x is a variable.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]942
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]943<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]944is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]945correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]946
947<li>clang does not support __builtin_apply and friends; this extension is
948extremely obscure and difficult to implement reliably.</li>
949
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]950</ul>
951
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]952<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
953<h3 id="c_ms">Microsoft extensions</h3>
954<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
955
956<p>clang has some experimental support for extensions from
957Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]958option. This is the default for Windows targets. Note that the
959support is incomplete; enabling Microsoft extensions will silently drop
960certain constructs (including __declspec and Microsoft-style asm statements).
961</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]962
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]963<ul>
Douglas Gregord3b227d2010-12-14 16:21:49 +0000[diff] [blame]964<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]965is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
966what Windows SDK and c++stdlib headers clang can compile. This option will be
967removed when clang supports the full set of MS extensions required for these
968headers.</li>
969
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]970<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]971record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]972
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]973<li>clang supports the Microsoft "#pragma pack" feature for
974controlling record layout. GCC also contains support for this feature,
975however where MSVC and GCC are incompatible clang follows the MSVC
976definition.</li>
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]977</ul>
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]978
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]979<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]980<h2 id="target_features">Target-Specific Features and Limitations</h2>
981<!-- ======================================================================= -->
982
983
984<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
985<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
986<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
987
988<!-- ======================== -->
989<h4 id="target_arch_x86">X86</h4>
990<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]991
992<p>The support for X86 (both 32-bit and 64-bit) is considered stable on Darwin
993(Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to correctly
994compile many large C, C++, Objective-C, and Objective-C++ codebases.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]995
NAKAMURA Takumiddf68ff2011-04-05 04:31:31 +0000[diff] [blame]996<p>On x86_64-mingw32, passing i128(by value) is incompatible to Microsoft x64
997calling conversion. You might need to tweak WinX86_64ABIInfo::classify()
998in lib/CodeGen/TargetInfo.cpp.</p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]999
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1000<!-- ======================== -->
1001<h4 id="target_arch_arm">ARM</h4>
1002<!-- ======================== -->
Daniel Dunbarbcaf7aa2010-09-19 19:26:59 +0000[diff] [blame]1003
1004<p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable on
1005Darwin (iOS): it has been tested to correctly compile many large C, C++,
Bob Wilson4ea8dfa2011-01-10 17:55:14 +0000[diff] [blame]1006Objective-C, and Objective-C++ codebases. Clang only supports a limited number
1007of ARM architectures. It does not yet fully support ARMv5, for example.</p>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1008
1009<!-- ======================== -->
1010<h4 id="target_arch_other">Other platforms</h4>
1011<!-- ======================== -->
1012clang currently contains some support for PPC and Sparc; however, significant
1013pieces of code generation are still missing, and they haven't undergone
1014significant testing.
1015
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]1016<p>clang contains limited support for the MSP430 embedded processor, but both
1017the clang support and the LLVM backend support are highly experimental.
1018
1019<p>Other platforms are completely unsupported at the moment. Adding the
1020minimal support needed for parsing and semantic analysis on a new platform
1021is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
1022of support is also sufficient for conversion to LLVM IR for simple programs.
1023Proper support for conversion to LLVM IR requires adding code to
1024lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
1025Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1026
1027<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1028<h3 id="target_os">Operating System Features and Limitations</h3>
1029<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1030
1031<!-- ======================================= -->
1032<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
1033<!-- ======================================= -->
1034
1035<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
1036
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1037<!-- ======================================= -->
1038<h4 id="target_os_win32">Windows</h4>
1039<!-- ======================================= -->
1040
1041<p>Experimental supports are on Cygming.</p>
1042
1043<h5>Cygwin</h5>
1044
1045<p>Clang works on Cygwin-1.7.</p>
1046
1047<h5>MinGW32</h5>
1048
1049<p>Clang works on some mingw32 distributions.
1050Clang assumes directories as below;</p>
1051
1052<ul>
1053<li><tt>C:/mingw/include</tt></li>
1054<li><tt>C:/mingw/lib</tt></li>
1055<li><tt>C:/mingw/lib/gcc/mingw32/4.[3-5].0/include/c++</tt></li>
1056</ul>
1057
1058<p>On MSYS, a few tests might fail. It is due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8520">Bug 8520</a> and is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110314/118106.html">LLVM's r127724</a>.</p>
1059
1060<h5>MinGW-w64</h5>
1061
1062<p>For x32(i686-w64-mingw32), it is not supported yet.</p>
1063
Chris Lattnerfc8f0e12011-04-15 05:22:18 +0000[diff] [blame]1064<p>For x64(x86_64-w64-mingw32), <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">an essential patch(LLVM's r128206)</a> would be needed. It is incompatible to <a href="http://tdm-gcc.tdragon.net/development">TDM-GCC</a> due to the definition of symbol &quot;<code>___chkstk</code>&quot;. Clang assumes as below;<p>
NAKAMURA Takumia75fdb22011-04-04 15:02:41 +0000[diff] [blame]1065
1066<ul>
1067<li><tt>C:/mingw/x86_64-w64-mingw32/include</tt></li>
1068<li><tt>C:/mingw/x86_64-w64-mingw32/include/c++/4.5.[23]</tt></li>
1069<li>GCC driver &quot;gcc.exe&quot; to build x86_64-w64-mingw32 binary.</li>
1070</ul>
1071
1072<p><a href="http://llvm.org/bugs/show_bug.cgi?id=8833">Some tests might fail</a>
1073on x64.</p>
1074
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]1075</div>
1076</body>
1077</html>