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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>
35 <li><a href="#diagnostics">Controlling Errors and Warnings</a></li>
36 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
37 </ul>
38</li>
39<li><a href="#c">C Language Features</a>
40 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]41 <li><a href="#c_ext">Extensions supported by clang</a></li>
42 <li><a href="#c_modes">Differences between various standard modes</a></li>
43 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
44 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
45 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]46 </ul>
47</li>
48<li><a href="#objc">Objective-C Language Features</a>
49 <ul>
50 <li><a href="#objc_incompatibilities">Intentional Incompatibilities with
51 GCC</a></li>
52 </ul>
53</li>
54<li><a href="#cxx">C++ Language Features</a>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]55</li>
56<li><a href="#objcxx">Objective C++ Language Features</a>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]57</li>
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>
71 </ul>
72
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.
123Please see the <a href="target_features">Target-Specific Features and
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
185<!-- ================================================= -->
186<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
187<!-- ================================================= -->
188
189<p>Clang aims to produce beautiful diagnostics by default, particularly for new
190users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]191preferences, and sometimes Clang is driven by another program that wants to
192parse simple and consistent output, not a person. For these cases, Clang
193provides a wide range of options to control the exact output format of the
194diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]195
196<dl>
197
198<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
199<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
200diagnostic.</dt>
201<dd>This option, which defaults to on, controls whether or not Clang prints the
202column number of a diagnostic. For example, when this is enabled, Clang will
203print something like:</p>
204
205<pre>
206 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
207 #endif bad
208 ^
209 //
210</pre>
211
212<p>When this is disabled, Clang will print "test.c:28: warning..." with no
213column number.</p>
214</dd>
215
216<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
217<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
218source file/line/column information in diagnostic.</dt>
219<dd>This option, which defaults to on, controls whether or not Clang prints the
220filename, line number and column number of a diagnostic. For example,
221when this is enabled, Clang will print something like:</p>
222
223<pre>
224 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
225 #endif bad
226 ^
227 //
228</pre>
229
230<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
231</dd>
232
233<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
234<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
235line and ranges from source code in diagnostic.</dt>
236<dd>This option, which defaults to on, controls whether or not Clang prints the
237source line, source ranges, and caret when emitting a diagnostic. For example,
238when this is enabled, Clang will print something like:</p>
239
240<pre>
241 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
242 #endif bad
243 ^
244 //
245</pre>
246
247<p>When this is disabled, Clang will just print:</p>
248
249<pre>
250 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
251</pre>
252
253</dd>
254
255<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
256<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
257Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
258<dd>This option, which defaults to on,
259controls whether or not Clang prints the associated <A
260href="#cl_diag_warning_groups">warning group</a> option name when outputting
261a warning diagnostic. For example, in this output:</p>
262
263<pre>
264 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
265 #endif bad
266 ^
267 //
268</pre>
269
270<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
271the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
272diagnostic. This information tells you the flag needed to enable or disable the
273diagnostic, either from the command line or through <a
274href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
275
276
277<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
278<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
279Enable "FixIt" information in the diagnostics output.</dt>
280<dd>This option, which defaults to on, controls whether or not Clang prints the
281information on how to fix a specific diagnostic underneath it when it knows.
282For example, in this output:</p>
283
284<pre>
285 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
286 #endif bad
287 ^
288 //
289</pre>
290
291<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
292the "//" line at the end of the message. This information is useful for users
293who may not understand what is wrong, but can be confusing for machine
294parsing.</p>
295</dd>
296
297<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]298<dt id="opt_fdiagnostics-print-source-range-info">
299<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]300Print machine parsable information about source ranges.</dt>
301<dd>This option, which defaults to off, controls whether or not Clang prints
302information about source ranges in a machine parsable format after the
303file/line/column number information. The information is a simple sequence of
304brace enclosed ranges, where each range lists the start and end line/column
305locations. For example, in this output:</p>
306
307<pre>
308exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
309 P = (P-42) + Gamma*4;
310 ~~~~~~ ^ ~~~~~~~
311</pre>
312
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]313<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]314</dd>
315
316
317</dl>
318
319
320
321
322<!-- ===================================================== -->
323<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
324<!-- ===================================================== -->
325
326<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
327
328
329<dl>
330
331
332<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
333<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
334 the end of a preprocessor directive.</dt>
335<dd>This option, which defaults to on, enables warnings about extra tokens at
336the end of preprocessor directives. For example:</p>
337
338<pre>
339 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
340 #endif bad
341 ^
342</pre>
343
344<p>These extra tokens are not strictly conforming, and are usually best handled
345by commenting them out.</p>
346
347<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
348 and <a href="">-Wbaz</a>.</p>
349</dd>
350
351</dl>
352
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]353<!-- ======================================================================= -->
354<h2 id="general_features">Language and Target-Independent Features</h2>
355<!-- ======================================================================= -->
356
357
358<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
359<h3 id="diagnostics">Controlling Errors and Warnings</h3>
360<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
361
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]362<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]363emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]364
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]365<h4>Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]366
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]367<p>When Clang emits a diagnostic, it includes rich information in the output,
368and gives you fine-grain control over which information is printed. Clang has
369the ability to print this information, and these are the options that control
370it:</p>
371
372<p>
373<ol>
374<li>A file/line/column indicator that shows exactly where the diagnostic occurs
375 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
376 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
377<li>A categorization of the diagnostic as a note, warning, error, or fatal
378 error.</li>
379<li>A text string that describes what the problem is.</li>
380<li>An option that indicates how to control the diagnostic (for diagnostics that
381 support it) [<a
382 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
383<li>The line of source code that the issue occurs on, along with a caret and
384 ranges that indicate the important locations [<a
385 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
386<li>"FixIt" information, which is a concise explanation of how to fix the
387 problem (when Clang is certain it knows) [<a
388 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
389<li>A machine-parsable representation of the ranges involved (off by
390 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]391 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]392</ol></p>
393
394<p>For more information please see <a href="#cl_diag_formatting">Formatting of
395Diagnostics</a>.</p>
396
397<h4>Controlling Which Diagnostics Clang Generates</h4>
398
399<p>mappings: ignore, note, warning, error, fatal</p>
400
401<p>
402The two major classes are control from the command line and control via pragmas
403in your code.</p>
404
405
406<p>-W flags, -pedantic, etc</p>
407
408<p>pragma GCC diagnostic</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]409
410<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
411<h3 id="precompiledheaders">Precompiled Headers</h3>
412<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
413
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]414<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
415headers</a> are a general approach employed by many compilers to reduce
416compilation time. The underlying motivation of the approach is that it is
417common for the same (and often large) header files to be included by
418multiple source files. Consequently, compile times can often be greatly improved
419by caching some of the (redundant) work done by a compiler to process headers.
420Precompiled header files, which represent one of many ways to implement
421this optimization, are literally files that represent an on-disk cache that
422contains the vital information necessary to reduce some of the work
423needed to process a corresponding header file. While details of precompiled
424headers vary between compilers, precompiled headers have been shown to be a
425highly effective at speeding up program compilation on systems with very large
426system headers (e.g., Mac OS/X).</p>
427
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]428<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]429
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]430<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]431the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
432interface in GCC for generating PCH files:</p>
433
434<pre>
435 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]436 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]437</pre>
438
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]439<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]440
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]441<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]442<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
443
444<pre>
445 $ clang -include test.h test.c -o test
446</pre>
447
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]448<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]449is 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]450will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]451directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
452GCC.</p>
453
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]454<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]455for headers that are directly included within a source file. For example:</p>
456
457<pre>
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]458 $ clang -x c-header test.h -o test.h.cth
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]459 $ cat test.c
460 #include "test.h"
461 $ clang test.c -o test
462</pre>
463
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]464<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]465<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
466and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]467
468
469<!-- ======================================================================= -->
470<h2 id="c">C Language Features</h2>
471<!-- ======================================================================= -->
472
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]473<p>The support for standard C in clang is feature-complete except for the C99
474floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]475
476<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]477<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]478<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
479
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]480<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]481
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]482<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
483<h3 id="c_modes">Differences between various standard modes</h3>
484<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]485
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]486<p>clang supports the -std option, which changes what language mode clang uses.
487The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
488for those modes. If no -std option is specified, clang defaults to gnu99 mode.
489</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]490
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]491<p>Differences between all c* and gnu* modes:</p>
492<ul>
493<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]494<li>Target-specific defines not prefixed by underscores, like "linux", are
495defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]496<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
497-trigraphs option.</li>
498<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
499variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]500<li>The Apple "blocks" extension is recognized by default in gnu* modes
501on some platforms; it can be enabled in any mode with the "-fblocks"
502option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]503<li>Some warnings are different.</li>
504</ul>
505
506<p>Differences between *89 and *99 modes:</p>
507<ul>
508<li>The *99 modes default to implementing "inline" as specified in C99, while
509the *89 modes implement the GNU version. This can be overridden for individual
510functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]511<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]512<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
513statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
514<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]515<li>"inline" is not recognized as a keyword in c89 mode.</li>
516<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]517<li>Commas are allowed in integer constant expressions in *99 modes.</li>
518<li>Arrays which are not lvalues are not implicitly promoted to pointers in
519*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]520<li>Some warnings are different.</li>
521</ul>
522
523<p>c94 mode is identical to c89 mode except that digraphs are enabled in
524c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
525
526<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
527<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
528<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
529
530<p>clang tries to be compatible with gcc as much as possible, but some gcc
531extensions are not implemented yet:</p>
532
533<ul>
534<li>clang does not support __label__
535(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
536a relatively small feature, so it is likely to be implemented relatively
537soon.</li>
538
539<li>clang does not support attributes on function pointers
540(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 2461</a>). This is
541a relatively important feature, so it is likely to be implemented relatively
542soon.</li>
543
544<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]545(<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]546the uses described in the bug, this is likely to be implemented at some
547point, at least partially.</li>
548
549<li>clang does not support #pragma align
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]550(<a href="http://llvm.org/bugs/show_bug.cgi?id=3811">bug 3811</a>). This is a
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]551relatively small feature, so it is likely to be implemented relatively
552soon.</li>
553
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]554<li>clang does not support code generation for local variables pinned to
555registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
556This is a relatively small feature, so it is likely to be implemented
557relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]558
559<li>clang does not support decimal floating point types (_Decimal32 and
560friends) or fixed-point types (_Fract and friends); nobody has expressed
561interest in these features yet, so it's hard to say when they will be
562implemented.</li>
563
564<li>clang does not support nested functions; this is a complex feature which
565is infrequently used, so it is unlikely to be implemented anytime soon.</li>
566
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]567<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]568to be implemented soon because it requires additional LLVM backend support.
569</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]570
571<li>clang does not support static initialization of flexible array
572members. This appears to be a rarely used extension, but could be
573implemented pending user demand.</li>
574
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]575<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
576This is used rarely, but in some potentially interesting places, like the
577glibc headers, so it may be implemented pending user demand. Note that
578because clang pretends to be like GCC 4.2, and this extension was introduced
579in 4.3, the glibc headers will not try to use this extension with clang at
580the moment.</li>
581
582<li>clang does not support the gcc extension for forward-declaring function
583parameters; this has not showed up in any real-world code yet, though, so it
584might never be implemented.</li>
585
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]586</ul>
587
588<p>This is not a complete list; if you find an unsupported extension
589missing from this list, please send an e-mail to cfe-dev. This list
590currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
591Also, this list does not include bugs in mostly-implemented features; please
592see 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">
593bug tracker</a> for known existing bugs (FIXME: Is there a section for
594bug-reporting guidelines somewhere?).</p>
595
596<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
597<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
598<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
599
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame^]600<ul>
601
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]602<li>clang does not support the gcc extension that allows variable-length arrays
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]603in structures. This is for a few of reasons: one, it is tricky
604to implement, two, the extension is completely undocumented, and three, the
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]605extension appears to be rarely used.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]606
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]607<li>clang does not support duplicate definitions of a function where one is
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]608inline. This complicates clients of the AST which normally can expect there is
609at most one definition for each function. Source code using this feature should
610be changed to define the inline and out-of-line definitions in separate
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]611translation units.</li>
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]612
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]613<li>clang does not have an equivalent to gcc's "fold"; this means that
614clang doesn't accept some constructs gcc might accept in contexts where a
615constant expression is required, like "x-x" where x is a variable, or calls
616to C library functions like strlen.</li>
617
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]618<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]619is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]620correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]621
622<li>clang does not support __builtin_apply and friends; this extension is
623extremely obscure and difficult to implement reliably.</li>
624
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame^]625</ul>
626
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]627<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
628<h3 id="c_ms">Microsoft extensions</h3>
629<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
630
631<p>clang has some experimental support for extensions from
632Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]633option. This is the default for Windows targets. Note that the
634support is incomplete; enabling Microsoft extensions will silently drop
635certain constructs (including __declspec and Microsoft-style asm statements).
636</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]637
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]638<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]639record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]640
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]641<li>clang supports the Microsoft "#pragma pack" feature for
642controlling record layout. GCC also contains support for this feature,
643however where MSVC and GCC are incompatible clang follows the MSVC
644definition.</li>
645
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]646<!-- ======================================================================= -->
647<h2 id="objc">Objective-C Language Features</h2>
648<!-- ======================================================================= -->
649
650
651<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
652<h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3>
653<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
654
655<p>No cast of super, no lvalue casts.</p>
656
657
658
659<!-- ======================================================================= -->
660<h2 id="cxx">C++ Language Features</h2>
661<!-- ======================================================================= -->
662
663<p>At this point, Clang C++ is not generally useful. However, Clang C++ support
664is under active development and is progressing rapidly. Please see the <a
665href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or
666ask on the mailing list about how you can help.</p>
667
668<p>Note that the clang driver will refuse to even try to use clang to compile
669C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If
670you really want to play with Clang's C++ support, please pass that flag. </p>
671
672<!-- ======================================================================= -->
673<h2 id="objcxx">Objective C++ Language Features</h2>
674<!-- ======================================================================= -->
675
676<p>At this point, Clang C++ support is not generally useful (and therefore,
677neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for
678more information.</p>
679
680<!-- ======================================================================= -->
681<h2 id="target_features">Target-Specific Features and Limitations</h2>
682<!-- ======================================================================= -->
683
684
685<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
686<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
687<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
688
689<!-- ======================== -->
690<h4 id="target_arch_x86">X86</h4>
691<!-- ======================== -->
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]692<p>The support for X86 (both 32-bit and 64-bit) is considered stable
693on Darwin (Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to
694correctly compile large C and Objective-C codebases. (FIXME: Anything specific
695we want to say here? Possibly mention some LLVM x86 limitations?)
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]696
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]697<!-- ======================== -->
698<h4 id="target_arch_arm">ARM</h4>
699<!-- ======================== -->
700ARM support is mostly feature-complete, but still experimental; it hasn't
701undergone significant testing.
702
703<!-- ======================== -->
704<h4 id="target_arch_other">Other platforms</h4>
705<!-- ======================== -->
706clang currently contains some support for PPC and Sparc; however, significant
707pieces of code generation are still missing, and they haven't undergone
708significant testing.
709
710<p>clang contains some support for the embedded PIC16 processor
711(FIXME: I haven't been keeping track of this; what should this say?).
712
713<p>clang contains limited support for the MSP430 embedded processor, but both
714the clang support and the LLVM backend support are highly experimental.
715
716<p>Other platforms are completely unsupported at the moment. Adding the
717minimal support needed for parsing and semantic analysis on a new platform
718is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
719of support is also sufficient for conversion to LLVM IR for simple programs.
720Proper support for conversion to LLVM IR requires adding code to
721lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
722Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]723
724<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
725<h3 id="target_os">Operating System Features and Limitations</h3>
726<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
727
728<!-- ======================================= -->
729<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
730<!-- ======================================= -->
731
732<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
733
734</div>
735</body>
736</html>