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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>
55 <ul>
56 <li>...</li>
57 </ul>
58</li>
59<li><a href="#objcxx">Objective C++ Language Features</a>
60 <ul>
61 <li>...</li>
62 </ul>
63</li>
64<li><a href="#target_features">Target-Specific Features and Limitations</a>
65 <ul>
66 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
67 <ul>
68 <li><a href="#target_arch_x86">X86</a></li>
69 <li>PPC</li>
70 <li>ARM</li>
71 </ul>
72 </li>
73 <li><a href="#target_os">Operating System Features and Limitations</a>
74 <ul>
75 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
76 <li>Linux, etc.</li>
77 </ul>
78
79 </li>
80 </ul>
81</li>
82</ul>
83
84
85<!-- ======================================================================= -->
86<h2 id="intro">Introduction</h2>
87<!-- ======================================================================= -->
88
89<p>The Clang Compiler is an open-source compiler for the C family of programming
90languages, aiming to be the best in class implementation of these languages.
91Clang builds on the LLVM optimizer and code generator, allowing it to provide
92high-quality optimization and code generation support for many targets. For
93more general information, please see the <a href="http://clang.llvm.org">Clang
94Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
95
96<p>This document describes important notes about using Clang as a compiler for
97an end-user, documenting the supported features, command line options, etc. If
98you are interested in using Clang to build a tool that processes code, please
99see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
100interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
101Static Analyzer</a>, please see its web page.</p>
102
103<p>Clang is designed to support the C family of programming languages, which
104includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
105href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
106dialects of those. For language-specific information, please see the
107corresponding language specific section:</p>
108
109<ul>
110<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
111 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
112<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
113 variants depending on base language.</li>
114<li><a href="#cxx">C++ Language Features</a></li>
115<li><a href="#objcxx">Objective C++ Language</a></li>
116</ul>
117
118<p>In addition to these base languages and their dialects, Clang supports a
119broad variety of language extensions, which are documented in the corresponding
120language section. These extensions are provided to be compatible with the GCC,
121Microsoft, and other popular compilers as well as to improve functionality
122through Clang-specific features. The Clang driver and language features are
123intentionally designed to be as compatible with the GNU GCC compiler as
124reasonably possible, easing migration from GCC to Clang. In most cases, code
125"just works".</p>
126
127<p>In addition to language specific features, Clang has a variety of features
128that depend on what CPU architecture or operating system is being compiled for.
129Please see the <a href="target_features">Target-Specific Features and
130Limitations</a> section for more details.</p>
131
132<p>The rest of the introduction introduces some basic <a
133href="#terminology">compiler terminology</a> that is used throughout this manual
134and contains a basic <a href="#basicusage">introduction to using Clang</a>
135as a command line compiler.</p>
136
137<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
138<h3 id="terminology">Terminology</h3>
139<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
140
141<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
142 optimizer</p>
143
144<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
145<h3 id="basicusage">Basic Usage</h3>
146<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
147
148<p>Intro to how to use a C compiler for newbies.</p>
149<p>
150compile + link
151
152compile then link
153
154debug info
155
156enabling optimizations
157
158picking a language to use, defaults to C99 by default. Autosenses based on
159extension.
160
161using a makefile
162</p>
163
164
165<!-- ======================================================================= -->
166<h2 id="commandline">Command Line Options</h2>
167<!-- ======================================================================= -->
168
169<p>
170This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]171depth on the ones that are covered by other sections. However, the first part
172introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]173</p>
174
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]175
176<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
177<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
178<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
179
180<p><b>-Werror</b>: Turn warnings into errors.</p>
181<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
182<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
183 specified.</p>
184<p><b>-Wfoo</b>: Enable warning foo</p>
185<p><b>-Wno-foo</b>: Disable warning foo</p>
186<p><b>-w</b>: Disable all warnings.</p>
187<p><b>-pedantic</b>: Warn on language extensions.</p>
188<p><b>-pedantic-errors</b>: Error on language extensions.</p>
189<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
190
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
209print something like:</p>
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,
227when this is enabled, Clang will print something like:</p>
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,
244when this is enabled, Clang will print something like:</p>
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>
252
253<p>When this is disabled, Clang will just print:</p>
254
255<pre>
256 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
257</pre>
258
259</dd>
260
261<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
262<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
263Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
264<dd>This option, which defaults to on,
265controls whether or not Clang prints the associated <A
266href="#cl_diag_warning_groups">warning group</a> option name when outputting
267a warning diagnostic. For example, in this output:</p>
268
269<pre>
270 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
271 #endif bad
272 ^
273 //
274</pre>
275
276<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
277the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
278diagnostic. This information tells you the flag needed to enable or disable the
279diagnostic, either from the command line or through <a
280href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
281
282
283<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
284<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
285Enable "FixIt" information in the diagnostics output.</dt>
286<dd>This option, which defaults to on, controls whether or not Clang prints the
287information on how to fix a specific diagnostic underneath it when it knows.
288For example, in this output:</p>
289
290<pre>
291 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
292 #endif bad
293 ^
294 //
295</pre>
296
297<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
298the "//" line at the end of the message. This information is useful for users
299who may not understand what is wrong, but can be confusing for machine
300parsing.</p>
301</dd>
302
303<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]304<dt id="opt_fdiagnostics-print-source-range-info">
305<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]306Print machine parsable information about source ranges.</dt>
307<dd>This option, which defaults to off, controls whether or not Clang prints
308information about source ranges in a machine parsable format after the
309file/line/column number information. The information is a simple sequence of
310brace enclosed ranges, where each range lists the start and end line/column
311locations. For example, in this output:</p>
312
313<pre>
314exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
315 P = (P-42) + Gamma*4;
316 ~~~~~~ ^ ~~~~~~~
317</pre>
318
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]319<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]320</dd>
321
322
323</dl>
324
325
326
327
328<!-- ===================================================== -->
329<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
330<!-- ===================================================== -->
331
332<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
333
334
335<dl>
336
337
338<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
339<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
340 the end of a preprocessor directive.</dt>
341<dd>This option, which defaults to on, enables warnings about extra tokens at
342the end of preprocessor directives. For example:</p>
343
344<pre>
345 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
346 #endif bad
347 ^
348</pre>
349
350<p>These extra tokens are not strictly conforming, and are usually best handled
351by commenting them out.</p>
352
353<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
354 and <a href="">-Wbaz</a>.</p>
355</dd>
356
357</dl>
358
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]359<!-- ======================================================================= -->
360<h2 id="general_features">Language and Target-Independent Features</h2>
361<!-- ======================================================================= -->
362
363
364<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
365<h3 id="diagnostics">Controlling Errors and Warnings</h3>
366<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
367
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]368<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]369emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]370
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]371<h4>Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]372
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]373<p>When Clang emits a diagnostic, it includes rich information in the output,
374and gives you fine-grain control over which information is printed. Clang has
375the ability to print this information, and these are the options that control
376it:</p>
377
378<p>
379<ol>
380<li>A file/line/column indicator that shows exactly where the diagnostic occurs
381 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
382 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
383<li>A categorization of the diagnostic as a note, warning, error, or fatal
384 error.</li>
385<li>A text string that describes what the problem is.</li>
386<li>An option that indicates how to control the diagnostic (for diagnostics that
387 support it) [<a
388 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
389<li>The line of source code that the issue occurs on, along with a caret and
390 ranges that indicate the important locations [<a
391 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
392<li>"FixIt" information, which is a concise explanation of how to fix the
393 problem (when Clang is certain it knows) [<a
394 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
395<li>A machine-parsable representation of the ranges involved (off by
396 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]397 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]398</ol></p>
399
400<p>For more information please see <a href="#cl_diag_formatting">Formatting of
401Diagnostics</a>.</p>
402
403<h4>Controlling Which Diagnostics Clang Generates</h4>
404
405<p>mappings: ignore, note, warning, error, fatal</p>
406
407<p>
408The two major classes are control from the command line and control via pragmas
409in your code.</p>
410
411
412<p>-W flags, -pedantic, etc</p>
413
414<p>pragma GCC diagnostic</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]415
416<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
417<h3 id="precompiledheaders">Precompiled Headers</h3>
418<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
419
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]420<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
421headers</a> are a general approach employed by many compilers to reduce
422compilation time. The underlying motivation of the approach is that it is
423common for the same (and often large) header files to be included by
424multiple source files. Consequently, compile times can often be greatly improved
425by caching some of the (redundant) work done by a compiler to process headers.
426Precompiled header files, which represent one of many ways to implement
427this optimization, are literally files that represent an on-disk cache that
428contains the vital information necessary to reduce some of the work
429needed to process a corresponding header file. While details of precompiled
430headers vary between compilers, precompiled headers have been shown to be a
431highly effective at speeding up program compilation on systems with very large
432system headers (e.g., Mac OS/X).</p>
433
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]434<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]435
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]436<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]437the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
438interface in GCC for generating PCH files:</p>
439
440<pre>
441 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]442 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]443</pre>
444
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]445<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]446
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]447<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]448<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
449
450<pre>
451 $ clang -include test.h test.c -o test
452</pre>
453
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]454<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]455is 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^]456will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]457directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
458GCC.</p>
459
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]460<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]461for headers that are directly included within a source file. For example:</p>
462
463<pre>
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]464 $ clang -x c-header test.h -o test.h.cth
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]465 $ cat test.c
466 #include "test.h"
467 $ clang test.c -o test
468</pre>
469
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame^]470<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]471<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
472and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]473
474
475<!-- ======================================================================= -->
476<h2 id="c">C Language Features</h2>
477<!-- ======================================================================= -->
478
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]479<p>The support for standard C in clang is feature-complete except for the C99
480floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]481
482<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]483<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]484<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
485
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]486<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]487
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]488<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
489<h3 id="c_modes">Differences between various standard modes</h3>
490<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]491
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]492<p>clang supports the -std option, which changes what language mode clang uses.
493The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
494for those modes. If no -std option is specified, clang defaults to gnu99 mode.
495</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]496
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]497<p>Differences between all c* and gnu* modes:</p>
498<ul>
499<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]500<li>Target-specific defines not prefixed by underscores, like "linux", are
501defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]502<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
503-trigraphs option.</li>
504<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
505variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]506<li>The Apple "blocks" extension is recognized by default in gnu* modes
507on some platforms; it can be enabled in any mode with the "-fblocks"
508option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]509<li>Some warnings are different.</li>
510</ul>
511
512<p>Differences between *89 and *99 modes:</p>
513<ul>
514<li>The *99 modes default to implementing "inline" as specified in C99, while
515the *89 modes implement the GNU version. This can be overridden for individual
516functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]517<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]518<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
519statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
520<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]521<li>"inline" is not recognized as a keyword in c89 mode.</li>
522<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]523<li>Commas are allowed in integer constant expressions in *99 modes.</li>
524<li>Arrays which are not lvalues are not implicitly promoted to pointers in
525*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]526<li>Some warnings are different.</li>
527</ul>
528
529<p>c94 mode is identical to c89 mode except that digraphs are enabled in
530c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
531
532<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
533<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
534<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
535
536<p>clang tries to be compatible with gcc as much as possible, but some gcc
537extensions are not implemented yet:</p>
538
539<ul>
540<li>clang does not support __label__
541(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
542a relatively small feature, so it is likely to be implemented relatively
543soon.</li>
544
545<li>clang does not support attributes on function pointers
546(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 2461</a>). This is
547a relatively important feature, so it is likely to be implemented relatively
548soon.</li>
549
550<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]551(<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]552the uses described in the bug, this is likely to be implemented at some
553point, at least partially.</li>
554
555<li>clang does not support #pragma align
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]556(<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]557relatively small feature, so it is likely to be implemented relatively
558soon.</li>
559
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]560<li>clang does not support code generation for local variables pinned to
561registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
562This is a relatively small feature, so it is likely to be implemented
563relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]564
565<li>clang does not support decimal floating point types (_Decimal32 and
566friends) or fixed-point types (_Fract and friends); nobody has expressed
567interest in these features yet, so it's hard to say when they will be
568implemented.</li>
569
570<li>clang does not support nested functions; this is a complex feature which
571is infrequently used, so it is unlikely to be implemented anytime soon.</li>
572
573<li>clang does not support __builtin_apply and friends; this extension requires
574complex code generator support that does not currently exist in LLVM, and there
575is very little demand, so it is unlikely to be implemented anytime soon.</li>
576
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]577<li>clang does not support global register variables, this is unlikely
578to be implemented soon.</li>
579
580<li>clang does not support static initialization of flexible array
581members. This appears to be a rarely used extension, but could be
582implemented pending user demand.</li>
583
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]584</ul>
585
586<p>This is not a complete list; if you find an unsupported extension
587missing from this list, please send an e-mail to cfe-dev. This list
588currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
589Also, this list does not include bugs in mostly-implemented features; please
590see 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">
591bug tracker</a> for known existing bugs (FIXME: Is there a section for
592bug-reporting guidelines somewhere?).</p>
593
594<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
595<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
596<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
597
598<p>clang does not support the gcc extension that allows variable-length arrays
599in structures. This is for a few of reasons: one, it is tricky
600to implement, two, the extension is completely undocumented, and three, the
601extension appears to be very rarely used.</p>
602
603<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
604<h3 id="c_ms">Microsoft extensions</h3>
605<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
606
607<p>clang has some experimental support for extensions from
608Microsoft Visual C++; to enable it, use the -fms-extensions command-line
609option. Eventually, this will be the default for Windows targets.
610These extensions are not anywhere near complete, so please do not
611file bugs; patches are welcome, though.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]612
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]613<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]614record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]615
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]616<li>clang supports the Microsoft "#pragma pack" feature for
617controlling record layout. GCC also contains support for this feature,
618however where MSVC and GCC are incompatible clang follows the MSVC
619definition.</li>
620
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]621<!-- ======================================================================= -->
622<h2 id="objc">Objective-C Language Features</h2>
623<!-- ======================================================================= -->
624
625
626<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
627<h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3>
628<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
629
630<p>No cast of super, no lvalue casts.</p>
631
632
633
634<!-- ======================================================================= -->
635<h2 id="cxx">C++ Language Features</h2>
636<!-- ======================================================================= -->
637
638<p>At this point, Clang C++ is not generally useful. However, Clang C++ support
639is under active development and is progressing rapidly. Please see the <a
640href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or
641ask on the mailing list about how you can help.</p>
642
643<p>Note that the clang driver will refuse to even try to use clang to compile
644C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If
645you really want to play with Clang's C++ support, please pass that flag. </p>
646
647<!-- ======================================================================= -->
648<h2 id="objcxx">Objective C++ Language Features</h2>
649<!-- ======================================================================= -->
650
651<p>At this point, Clang C++ support is not generally useful (and therefore,
652neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for
653more information.</p>
654
655<!-- ======================================================================= -->
656<h2 id="target_features">Target-Specific Features and Limitations</h2>
657<!-- ======================================================================= -->
658
659
660<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
661<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
662<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
663
664<!-- ======================== -->
665<h4 id="target_arch_x86">X86</h4>
666<!-- ======================== -->
667
668
669<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
670<h3 id="target_os">Operating System Features and Limitations</h3>
671<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
672
673<!-- ======================================= -->
674<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
675<!-- ======================================= -->
676
677<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
678
679</div>
680</body>
681</html>