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3<title>Clang Compiler User's Manual</title>
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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
434<p>Clang supports an implementation of precompiled headers known as
435<em>pre-tokenized headers</em> (PTH). Clang's pre-tokenized headers support most
436of same interfaces as GCC's pre-compiled headers (as well as others) but are
437completely different in their implementation. If you are interested in how
438PTH is implemented, please see the <a href="PTHInternals.html">PTH Internals
439 document</a>.</p>
440
441<h4>Generating a PTH File</h4>
442
443<p>To generate a PTH file using Clang, one invokes Clang with
444the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
445interface in GCC for generating PCH files:</p>
446
447<pre>
448 $ gcc -x c-header test.h -o test.h.gch
449 $ clang -x c-header test.h -o test.h.pth
450</pre>
451
452<h4>Using a PTH File</h4>
453
454<p>A PTH file can then be used as a prefix header when a
455<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
456
457<pre>
458 $ clang -include test.h test.c -o test
459</pre>
460
461<p>The <tt>clang</tt> driver will first check if a PTH file for <tt>test.h</tt>
462is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
463will be processed from the PTH file. Otherwise, Clang falls back to
464directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
465GCC.</p>
466
Ted Kremenekbf94ca62009-04-21 17:14:24 +0000[diff] [blame]467<p><b>NOTE:</b> Clang does <em>not</em> automatically use PTH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]468for headers that are directly included within a source file. For example:</p>
469
470<pre>
471 $ clang -x c-header test.h -o test.h.pth
472 $ cat test.c
473 #include "test.h"
474 $ clang test.c -o test
475</pre>
476
477<p>In this example, <tt>clang</tt> will not automatically use the PTH file for
478<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
479and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]480
481
482<!-- ======================================================================= -->
483<h2 id="c">C Language Features</h2>
484<!-- ======================================================================= -->
485
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]486<p>The support for standard C in clang is feature-complete except for the C99
487floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]488
489<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]490<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]491<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
492
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]493<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]494
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]495<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
496<h3 id="c_modes">Differences between various standard modes</h3>
497<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]498
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]499<p>clang supports the -std option, which changes what language mode clang uses.
500The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
501for those modes. If no -std option is specified, clang defaults to gnu99 mode.
502</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]503
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]504<p>Differences between all c* and gnu* modes:</p>
505<ul>
506<li>c* modes define "__STRICT_ANSI__".</li>
507<li>Target-specific defines not prefixed by underscores, like "linux", are defined
508in gnu* modes.</li>
509<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
510-trigraphs option.</li>
511<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
512variants "__asm__" and "__typeof__" are recognized in all modes.</li>
513<li>Some warnings are different.</li>
514</ul>
515
516<p>Differences between *89 and *99 modes:</p>
517<ul>
518<li>The *99 modes default to implementing "inline" as specified in C99, while
519the *89 modes implement the GNU version. This can be overridden for individual
520functions with the __gnu_inline__ attribute.</li>
521<li>Digraphs are enabled in the *99 modes.</li>
522<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
523statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
524<li>__STDC_VERSION__ is not defined in *89 modes.</li>
525<li>"inline" and "restrict" are not recognized as keywords in c89 mode.</li>
526<li>Commas are allowed in integer constant expressions in *99 modes.</li>
527<li>Arrays which are not lvalues are not implicitly promoted to pointers in
528*89 modes.</li>
529<li>Constructs like "&*X" are always allowed in *99 modes.</li>
530<li>Some warnings are different.</li>
531</ul>
532
533<p>c94 mode is identical to c89 mode except that digraphs are enabled in
534c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
535
536<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
537<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
538<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
539
540<p>clang tries to be compatible with gcc as much as possible, but some gcc
541extensions are not implemented yet:</p>
542
543<ul>
544<li>clang does not support __label__
545(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
546a relatively small feature, so it is likely to be implemented relatively
547soon.</li>
548
549<li>clang does not support attributes on function pointers
550(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 2461</a>). This is
551a relatively important feature, so it is likely to be implemented relatively
552soon.</li>
553
554<li>clang does not support #pragma weak
555(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 3679</a>). Due to
556the uses described in the bug, this is likely to be implemented at some
557point, at least partially.</li>
558
559<li>clang does not support #pragma align
560(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 3811</a>). This is a
561relatively small feature, so it is likely to be implemented relatively
562soon.</li>
563
564<li>clang does not implement overloads for the __sync_* builtins
565(<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 3824</a>). The
566builtins only currently work with 32-bit types. This is a relatively
567small feature, so it is likely to be implemented relatively soon.</li>
568
569<li>clang does not support code generation for variables pinned to registers
570(<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>). This
571is a relatively small feature, so it is likely to be implemented relatively
572soon.</li>
573
574<li>clang does not support decimal floating point types (_Decimal32 and
575friends) or fixed-point types (_Fract and friends); nobody has expressed
576interest in these features yet, so it's hard to say when they will be
577implemented.</li>
578
579<li>clang does not support nested functions; this is a complex feature which
580is infrequently used, so it is unlikely to be implemented anytime soon.</li>
581
582<li>clang does not support __builtin_apply and friends; this extension requires
583complex code generator support that does not currently exist in LLVM, and there
584is very little demand, so it is unlikely to be implemented anytime soon.</li>
585
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]586<li>clang does not support global register variables, this is unlikely
587to be implemented soon.</li>
588
589<li>clang does not support static initialization of flexible array
590members. This appears to be a rarely used extension, but could be
591implemented pending user demand.</li>
592
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]593</ul>
594
595<p>This is not a complete list; if you find an unsupported extension
596missing from this list, please send an e-mail to cfe-dev. This list
597currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
598Also, this list does not include bugs in mostly-implemented features; please
599see 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">
600bug tracker</a> for known existing bugs (FIXME: Is there a section for
601bug-reporting guidelines somewhere?).</p>
602
603<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
604<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
605<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
606
607<p>clang does not support the gcc extension that allows variable-length arrays
608in structures. This is for a few of reasons: one, it is tricky
609to implement, two, the extension is completely undocumented, and three, the
610extension appears to be very rarely used.</p>
611
612<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
613<h3 id="c_ms">Microsoft extensions</h3>
614<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
615
616<p>clang has some experimental support for extensions from
617Microsoft Visual C++; to enable it, use the -fms-extensions command-line
618option. Eventually, this will be the default for Windows targets.
619These extensions are not anywhere near complete, so please do not
620file bugs; patches are welcome, though.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]621
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]622<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame^]623record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]624
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]625<!-- ======================================================================= -->
626<h2 id="objc">Objective-C Language Features</h2>
627<!-- ======================================================================= -->
628
629
630<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
631<h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3>
632<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
633
634<p>No cast of super, no lvalue casts.</p>
635
636
637
638<!-- ======================================================================= -->
639<h2 id="cxx">C++ Language Features</h2>
640<!-- ======================================================================= -->
641
642<p>At this point, Clang C++ is not generally useful. However, Clang C++ support
643is under active development and is progressing rapidly. Please see the <a
644href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or
645ask on the mailing list about how you can help.</p>
646
647<p>Note that the clang driver will refuse to even try to use clang to compile
648C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If
649you really want to play with Clang's C++ support, please pass that flag. </p>
650
651<!-- ======================================================================= -->
652<h2 id="objcxx">Objective C++ Language Features</h2>
653<!-- ======================================================================= -->
654
655<p>At this point, Clang C++ support is not generally useful (and therefore,
656neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for
657more information.</p>
658
659<!-- ======================================================================= -->
660<h2 id="target_features">Target-Specific Features and Limitations</h2>
661<!-- ======================================================================= -->
662
663
664<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
665<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
666<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
667
668<!-- ======================== -->
669<h4 id="target_arch_x86">X86</h4>
670<!-- ======================== -->
671
672
673<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
674<h3 id="target_os">Operating System Features and Limitations</h3>
675<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
676
677<!-- ======================================= -->
678<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
679<!-- ======================================= -->
680
681<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
682
683</div>
684</body>
685</html>