| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 1 | <html> |
| 2 | <head> |
| 3 | <title>Clang Compiler User's Manual</title> |
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| 14 | <!--#include virtual="../menu.html.incl"--> |
| 15 | |
| 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 Lattner | 65a795b | 2009-04-20 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 Lattner | cf17d9d | 2009-04-20 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 Friedman | 660a5ac | 2009-04-28 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 Lattner | cf17d9d | 2009-04-20 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 |
| 90 | languages, aiming to be the best in class implementation of these languages. |
| 91 | Clang builds on the LLVM optimizer and code generator, allowing it to provide |
| 92 | high-quality optimization and code generation support for many targets. For |
| 93 | more general information, please see the <a href="http://clang.llvm.org">Clang |
| 94 | Web 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 |
| 97 | an end-user, documenting the supported features, command line options, etc. If |
| 98 | you are interested in using Clang to build a tool that processes code, please |
| 99 | see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are |
| 100 | interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang |
| 101 | Static Analyzer</a>, please see its web page.</p> |
| 102 | |
| 103 | <p>Clang is designed to support the C family of programming languages, which |
| 104 | includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a |
| 105 | href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many |
| 106 | dialects of those. For language-specific information, please see the |
| 107 | corresponding language specific section:</p> |
| 108 | |
| 109 | <ul> |
| 110 | <li><a href="#c">C Language</a>: K&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 |
| 119 | broad variety of language extensions, which are documented in the corresponding |
| 120 | language section. These extensions are provided to be compatible with the GCC, |
| 121 | Microsoft, and other popular compilers as well as to improve functionality |
| 122 | through Clang-specific features. The Clang driver and language features are |
| 123 | intentionally designed to be as compatible with the GNU GCC compiler as |
| 124 | reasonably 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 |
| 128 | that depend on what CPU architecture or operating system is being compiled for. |
| 129 | Please see the <a href="target_features">Target-Specific Features and |
| 130 | Limitations</a> section for more details.</p> |
| 131 | |
| 132 | <p>The rest of the introduction introduces some basic <a |
| 133 | href="#terminology">compiler terminology</a> that is used throughout this manual |
| 134 | and contains a basic <a href="#basicusage">introduction to using Clang</a> |
| 135 | as 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> |
| 150 | compile + link |
| 151 | |
| 152 | compile then link |
| 153 | |
| 154 | debug info |
| 155 | |
| 156 | enabling optimizations |
| 157 | |
| 158 | picking a language to use, defaults to C99 by default. Autosenses based on |
| 159 | extension. |
| 160 | |
| 161 | using a makefile |
| 162 | </p> |
| 163 | |
| 164 | |
| 165 | <!-- ======================================================================= --> |
| 166 | <h2 id="commandline">Command Line Options</h2> |
| 167 | <!-- ======================================================================= --> |
| 168 | |
| 169 | <p> |
| 170 | This section is generally an index into other sections. It does not go into |
| Chris Lattner | 65a795b | 2009-04-20 06:00:23 +0000 | [diff] [blame] | 171 | depth on the ones that are covered by other sections. However, the first part |
| 172 | introduces the language selection and other high level options like -c, -g, etc. |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 173 | </p> |
| 174 | |
| Chris Lattner | 65a795b | 2009-04-20 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 |
| 196 | users that first come to Clang. However, different people have different |
| Chris Lattner | 8217f4e | 2009-04-20 06:26:18 +0000 | [diff] [blame] | 197 | preferences, and sometimes Clang is driven by another program that wants to |
| 198 | parse simple and consistent output, not a person. For these cases, Clang |
| 199 | provides a wide range of options to control the exact output format of the |
| 200 | diagnostics that it generates.</p> |
| Chris Lattner | 65a795b | 2009-04-20 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 |
| 206 | diagnostic.</dt> |
| 207 | <dd>This option, which defaults to on, controls whether or not Clang prints the |
| 208 | column number of a diagnostic. For example, when this is enabled, Clang will |
| 209 | print 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 |
| 219 | column number.</p> |
| 220 | </dd> |
| 221 | |
| 222 | <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| 223 | <dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print |
| 224 | source file/line/column information in diagnostic.</dt> |
| 225 | <dd>This option, which defaults to on, controls whether or not Clang prints the |
| 226 | filename, line number and column number of a diagnostic. For example, |
| 227 | when 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 |
| 241 | line and ranges from source code in diagnostic.</dt> |
| 242 | <dd>This option, which defaults to on, controls whether or not Clang prints the |
| 243 | source line, source ranges, and caret when emitting a diagnostic. For example, |
| 244 | when 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>: |
| 263 | Enable <tt>[-Woption]</tt> information in diagnostic line.</dt> |
| 264 | <dd>This option, which defaults to on, |
| 265 | controls whether or not Clang prints the associated <A |
| 266 | href="#cl_diag_warning_groups">warning group</a> option name when outputting |
| 267 | a 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 |
| 277 | the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the |
| 278 | diagnostic. This information tells you the flag needed to enable or disable the |
| 279 | diagnostic, either from the command line or through <a |
| 280 | href="#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>: |
| 285 | Enable "FixIt" information in the diagnostics output.</dt> |
| 286 | <dd>This option, which defaults to on, controls whether or not Clang prints the |
| 287 | information on how to fix a specific diagnostic underneath it when it knows. |
| 288 | For 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 |
| 298 | the "//" line at the end of the message. This information is useful for users |
| 299 | who may not understand what is wrong, but can be confusing for machine |
| 300 | parsing.</p> |
| 301 | </dd> |
| 302 | |
| 303 | <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| Chris Lattner | 2a9cc23 | 2009-04-21 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 Lattner | 65a795b | 2009-04-20 06:00:23 +0000 | [diff] [blame] | 306 | Print machine parsable information about source ranges.</dt> |
| 307 | <dd>This option, which defaults to off, controls whether or not Clang prints |
| 308 | information about source ranges in a machine parsable format after the |
| 309 | file/line/column number information. The information is a simple sequence of |
| 310 | brace enclosed ranges, where each range lists the start and end line/column |
| 311 | locations. For example, in this output:</p> |
| 312 | |
| 313 | <pre> |
| 314 | exprs.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 Lattner | 2a9cc23 | 2009-04-21 05:35:32 +0000 | [diff] [blame] | 319 | <p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p> |
| Chris Lattner | 65a795b | 2009-04-20 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 |
| 342 | the 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 |
| 351 | by 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 Lattner | cf17d9d | 2009-04-20 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 Lattner | 65a795b | 2009-04-20 06:00:23 +0000 | [diff] [blame] | 368 | <p>Clang provides a number of ways to control which code constructs cause it to |
| Chris Lattner | 8217f4e | 2009-04-20 06:26:18 +0000 | [diff] [blame] | 369 | emit errors and warning messages, and how they are displayed to the console.</p> |
| Chris Lattner | 65a795b | 2009-04-20 06:00:23 +0000 | [diff] [blame] | 370 | |
| Chris Lattner | 8217f4e | 2009-04-20 06:26:18 +0000 | [diff] [blame] | 371 | <h4>Controlling How Clang Displays Diagnostics</h4> |
| Chris Lattner | 65a795b | 2009-04-20 06:00:23 +0000 | [diff] [blame] | 372 | |
| Chris Lattner | 8217f4e | 2009-04-20 06:26:18 +0000 | [diff] [blame] | 373 | <p>When Clang emits a diagnostic, it includes rich information in the output, |
| 374 | and gives you fine-grain control over which information is printed. Clang has |
| 375 | the ability to print this information, and these are the options that control |
| 376 | it:</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 Lattner | 2a9cc23 | 2009-04-21 05:35:32 +0000 | [diff] [blame] | 397 | href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li> |
| Chris Lattner | 8217f4e | 2009-04-20 06:26:18 +0000 | [diff] [blame] | 398 | </ol></p> |
| 399 | |
| 400 | <p>For more information please see <a href="#cl_diag_formatting">Formatting of |
| 401 | Diagnostics</a>.</p> |
| 402 | |
| 403 | <h4>Controlling Which Diagnostics Clang Generates</h4> |
| 404 | |
| 405 | <p>mappings: ignore, note, warning, error, fatal</p> |
| 406 | |
| 407 | <p> |
| 408 | The two major classes are control from the command line and control via pragmas |
| 409 | in your code.</p> |
| 410 | |
| 411 | |
| 412 | <p>-W flags, -pedantic, etc</p> |
| 413 | |
| 414 | <p>pragma GCC diagnostic</p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 415 | |
| 416 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 417 | <h3 id="precompiledheaders">Precompiled Headers</h3> |
| 418 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 419 | |
| Chris Lattner | 5c3074f | 2009-04-20 04:37:38 +0000 | [diff] [blame] | 420 | <p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled |
| 421 | headers</a> are a general approach employed by many compilers to reduce |
| 422 | compilation time. The underlying motivation of the approach is that it is |
| 423 | common for the same (and often large) header files to be included by |
| 424 | multiple source files. Consequently, compile times can often be greatly improved |
| 425 | by caching some of the (redundant) work done by a compiler to process headers. |
| 426 | Precompiled header files, which represent one of many ways to implement |
| 427 | this optimization, are literally files that represent an on-disk cache that |
| 428 | contains the vital information necessary to reduce some of the work |
| 429 | needed to process a corresponding header file. While details of precompiled |
| 430 | headers vary between compilers, precompiled headers have been shown to be a |
| 431 | highly effective at speeding up program compilation on systems with very large |
| 432 | system 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 |
| 436 | of same interfaces as GCC's pre-compiled headers (as well as others) but are |
| 437 | completely different in their implementation. If you are interested in how |
| 438 | PTH 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 |
| 444 | the <b><tt>-x <i><language></i>-header</tt></b> option. This mirrors the |
| 445 | interface 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> |
| 462 | is available; if so, the contents of <tt>test.h</tt> (and the files it includes) |
| 463 | will be processed from the PTH file. Otherwise, Clang falls back to |
| 464 | directly processing the content of <tt>test.h</tt>. This mirrors the behavior of |
| 465 | GCC.</p> |
| 466 | |
| Ted Kremenek | bf94ca6 | 2009-04-21 17:14:24 +0000 | [diff] [blame] | 467 | <p><b>NOTE:</b> Clang does <em>not</em> automatically use PTH files |
| Chris Lattner | 5c3074f | 2009-04-20 04:37:38 +0000 | [diff] [blame] | 468 | for 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 |
| 479 | and not specified on the command line using <tt>-include</tt>.</p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 480 | |
| 481 | |
| 482 | <!-- ======================================================================= --> |
| 483 | <h2 id="c">C Language Features</h2> |
| 484 | <!-- ======================================================================= --> |
| 485 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 486 | <p>The support for standard C in clang is feature-complete except for the C99 |
| 487 | floating-point pragmas.</p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 488 | |
| 489 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 490 | <h3 id="c_ext">Extensions supported by clang</h3> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 491 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 492 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 493 | <p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 494 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 495 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 496 | <h3 id="c_modes">Differences between various standard modes</h3> |
| 497 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 498 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 499 | <p>clang supports the -std option, which changes what language mode clang uses. |
| 500 | The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases |
| 501 | for those modes. If no -std option is specified, clang defaults to gnu99 mode. |
| 502 | </p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 503 | |
| Eli Friedman | 660a5ac | 2009-04-28 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> |
| Eli Friedman | 26fa0ed | 2009-05-27 23:02:57 +0000 | [diff] [blame^] | 507 | <li>Target-specific defines not prefixed by underscores, like "linux", are |
| 508 | defined in gnu* modes.</li> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 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 |
| 512 | variants "__asm__" and "__typeof__" are recognized in all modes.</li> |
| Eli Friedman | b0ac545 | 2009-05-16 23:17:30 +0000 | [diff] [blame] | 513 | <li>The Apple "blocks" extension is recognized by default in gnu* modes |
| 514 | on some platforms; it can be enabled in any mode with the "-fblocks" |
| 515 | option.</li> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 516 | <li>Some warnings are different.</li> |
| 517 | </ul> |
| 518 | |
| 519 | <p>Differences between *89 and *99 modes:</p> |
| 520 | <ul> |
| 521 | <li>The *99 modes default to implementing "inline" as specified in C99, while |
| 522 | the *89 modes implement the GNU version. This can be overridden for individual |
| 523 | functions with the __gnu_inline__ attribute.</li> |
| Eli Friedman | 26fa0ed | 2009-05-27 23:02:57 +0000 | [diff] [blame^] | 524 | <li>Digraphs are not recognized in c89 mode.</li> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 525 | <li>The scope of names defined inside a "for", "if", "switch", "while", or "do" |
| 526 | statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li> |
| 527 | <li>__STDC_VERSION__ is not defined in *89 modes.</li> |
| Eli Friedman | 26fa0ed | 2009-05-27 23:02:57 +0000 | [diff] [blame^] | 528 | <li>"inline" is not recognized as a keyword in c89 mode.</li> |
| 529 | <li>"restrict" is not recognized as a keyword in *89 modes.</li> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 530 | <li>Commas are allowed in integer constant expressions in *99 modes.</li> |
| 531 | <li>Arrays which are not lvalues are not implicitly promoted to pointers in |
| 532 | *89 modes.</li> |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 533 | <li>Some warnings are different.</li> |
| 534 | </ul> |
| 535 | |
| 536 | <p>c94 mode is identical to c89 mode except that digraphs are enabled in |
| 537 | c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p> |
| 538 | |
| 539 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 540 | <h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3> |
| 541 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 542 | |
| 543 | <p>clang tries to be compatible with gcc as much as possible, but some gcc |
| 544 | extensions are not implemented yet:</p> |
| 545 | |
| 546 | <ul> |
| 547 | <li>clang does not support __label__ |
| 548 | (<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is |
| 549 | a relatively small feature, so it is likely to be implemented relatively |
| 550 | soon.</li> |
| 551 | |
| 552 | <li>clang does not support attributes on function pointers |
| 553 | (<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 2461</a>). This is |
| 554 | a relatively important feature, so it is likely to be implemented relatively |
| 555 | soon.</li> |
| 556 | |
| 557 | <li>clang does not support #pragma weak |
| 558 | (<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 3679</a>). Due to |
| 559 | the uses described in the bug, this is likely to be implemented at some |
| 560 | point, at least partially.</li> |
| 561 | |
| 562 | <li>clang does not support #pragma align |
| 563 | (<a href="http://llvm.org/bugs/show_bug.cgi?id=2461">bug 3811</a>). This is a |
| 564 | relatively small feature, so it is likely to be implemented relatively |
| 565 | soon.</li> |
| 566 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 567 | <li>clang does not support code generation for variables pinned to registers |
| 568 | (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>). This |
| 569 | is a relatively small feature, so it is likely to be implemented relatively |
| 570 | soon.</li> |
| 571 | |
| 572 | <li>clang does not support decimal floating point types (_Decimal32 and |
| 573 | friends) or fixed-point types (_Fract and friends); nobody has expressed |
| 574 | interest in these features yet, so it's hard to say when they will be |
| 575 | implemented.</li> |
| 576 | |
| 577 | <li>clang does not support nested functions; this is a complex feature which |
| 578 | is infrequently used, so it is unlikely to be implemented anytime soon.</li> |
| 579 | |
| 580 | <li>clang does not support __builtin_apply and friends; this extension requires |
| 581 | complex code generator support that does not currently exist in LLVM, and there |
| 582 | is very little demand, so it is unlikely to be implemented anytime soon.</li> |
| 583 | |
| Daniel Dunbar | 05fa629 | 2009-05-12 23:12:07 +0000 | [diff] [blame] | 584 | <li>clang does not support global register variables, this is unlikely |
| 585 | to be implemented soon.</li> |
| 586 | |
| 587 | <li>clang does not support static initialization of flexible array |
| 588 | members. This appears to be a rarely used extension, but could be |
| 589 | implemented pending user demand.</li> |
| 590 | |
| Eli Friedman | 660a5ac | 2009-04-28 18:48:34 +0000 | [diff] [blame] | 591 | </ul> |
| 592 | |
| 593 | <p>This is not a complete list; if you find an unsupported extension |
| 594 | missing from this list, please send an e-mail to cfe-dev. This list |
| 595 | currently excludes C++; see <a href="#cxx">C++ Language Features</a>. |
| 596 | Also, this list does not include bugs in mostly-implemented features; please |
| 597 | see 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"> |
| 598 | bug tracker</a> for known existing bugs (FIXME: Is there a section for |
| 599 | bug-reporting guidelines somewhere?).</p> |
| 600 | |
| 601 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 602 | <h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3> |
| 603 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 604 | |
| 605 | <p>clang does not support the gcc extension that allows variable-length arrays |
| 606 | in structures. This is for a few of reasons: one, it is tricky |
| 607 | to implement, two, the extension is completely undocumented, and three, the |
| 608 | extension appears to be very rarely used.</p> |
| 609 | |
| 610 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 611 | <h3 id="c_ms">Microsoft extensions</h3> |
| 612 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 613 | |
| 614 | <p>clang has some experimental support for extensions from |
| 615 | Microsoft Visual C++; to enable it, use the -fms-extensions command-line |
| 616 | option. Eventually, this will be the default for Windows targets. |
| 617 | These extensions are not anywhere near complete, so please do not |
| 618 | file bugs; patches are welcome, though.</p> |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 619 | |
| Daniel Dunbar | 05fa629 | 2009-05-12 23:12:07 +0000 | [diff] [blame] | 620 | <li>clang does not support the Microsoft extension where anonymous |
| Daniel Dunbar | 869e054 | 2009-05-13 00:23:53 +0000 | [diff] [blame] | 621 | record members can be declared using user defined typedefs.</li> |
| Daniel Dunbar | 05fa629 | 2009-05-12 23:12:07 +0000 | [diff] [blame] | 622 | |
| Daniel Dunbar | 9375ed1 | 2009-05-13 21:40:49 +0000 | [diff] [blame] | 623 | <li>clang supports the Microsoft "#pragma pack" feature for |
| 624 | controlling record layout. GCC also contains support for this feature, |
| 625 | however where MSVC and GCC are incompatible clang follows the MSVC |
| 626 | definition.</li> |
| 627 | |
| Chris Lattner | cf17d9d | 2009-04-20 04:23:09 +0000 | [diff] [blame] | 628 | <!-- ======================================================================= --> |
| 629 | <h2 id="objc">Objective-C Language Features</h2> |
| 630 | <!-- ======================================================================= --> |
| 631 | |
| 632 | |
| 633 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 634 | <h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3> |
| 635 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 636 | |
| 637 | <p>No cast of super, no lvalue casts.</p> |
| 638 | |
| 639 | |
| 640 | |
| 641 | <!-- ======================================================================= --> |
| 642 | <h2 id="cxx">C++ Language Features</h2> |
| 643 | <!-- ======================================================================= --> |
| 644 | |
| 645 | <p>At this point, Clang C++ is not generally useful. However, Clang C++ support |
| 646 | is under active development and is progressing rapidly. Please see the <a |
| 647 | href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or |
| 648 | ask on the mailing list about how you can help.</p> |
| 649 | |
| 650 | <p>Note that the clang driver will refuse to even try to use clang to compile |
| 651 | C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If |
| 652 | you really want to play with Clang's C++ support, please pass that flag. </p> |
| 653 | |
| 654 | <!-- ======================================================================= --> |
| 655 | <h2 id="objcxx">Objective C++ Language Features</h2> |
| 656 | <!-- ======================================================================= --> |
| 657 | |
| 658 | <p>At this point, Clang C++ support is not generally useful (and therefore, |
| 659 | neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for |
| 660 | more information.</p> |
| 661 | |
| 662 | <!-- ======================================================================= --> |
| 663 | <h2 id="target_features">Target-Specific Features and Limitations</h2> |
| 664 | <!-- ======================================================================= --> |
| 665 | |
| 666 | |
| 667 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 668 | <h3 id="target_arch">CPU Architectures Features and Limitations</h3> |
| 669 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 670 | |
| 671 | <!-- ======================== --> |
| 672 | <h4 id="target_arch_x86">X86</h4> |
| 673 | <!-- ======================== --> |
| 674 | |
| 675 | |
| 676 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 677 | <h3 id="target_os">Operating System Features and Limitations</h3> |
| 678 | <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| 679 | |
| 680 | <!-- ======================================= --> |
| 681 | <h4 id="target_os_darwin">Darwin (Mac OS/X)</h4> |
| 682 | <!-- ======================================= --> |
| 683 | |
| 684 | <p>No __thread support, 64-bit ObjC support requires SL tools.</p> |
| 685 | |
| 686 | </div> |
| 687 | </body> |
| 688 | </html> |