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| |
| <h1>Clang Compiler User's Manual</h1> |
| |
| <ul> |
| <li><a href="#intro">Introduction</a> |
| <ul> |
| <li><a href="#terminology">Terminology</a></li> |
| <li><a href="#basicusage">Basic Usage</a></li> |
| </ul> |
| </li> |
| <li><a href="#commandline">Command Line Options</a> |
| <ul> |
| <li><a href="#cl_diagnostics">Options to Control Error and Warning |
| Messages</a></li> |
| </ul> |
| </li> |
| <li><a href="#general_features">Language and Target-Independent Features</a> |
| <ul> |
| <li><a href="#diagnostics">Controlling Errors and Warnings</a></li> |
| <li><a href="#precompiledheaders">Precompiled Headers</a></li> |
| </ul> |
| </li> |
| <li><a href="#c">C Language Features</a> |
| <ul> |
| <!-- <li><a href="#pragmas">Pragmas Supported</a></li> --> |
| <li><a href="#c_extensions">C Extensions Supported</a></li> |
| <li><a href="#c_incompatibilities">Intentional Incompatibilities with |
| GCC</a></li> |
| </ul> |
| </li> |
| <li><a href="#objc">Objective-C Language Features</a> |
| <ul> |
| <li><a href="#objc_incompatibilities">Intentional Incompatibilities with |
| GCC</a></li> |
| </ul> |
| </li> |
| <li><a href="#cxx">C++ Language Features</a> |
| <ul> |
| <li>...</li> |
| </ul> |
| </li> |
| <li><a href="#objcxx">Objective C++ Language Features</a> |
| <ul> |
| <li>...</li> |
| </ul> |
| </li> |
| <li><a href="#target_features">Target-Specific Features and Limitations</a> |
| <ul> |
| <li><a href="#target_arch">CPU Architectures Features and Limitations</a> |
| <ul> |
| <li><a href="#target_arch_x86">X86</a></li> |
| <li>PPC</li> |
| <li>ARM</li> |
| </ul> |
| </li> |
| <li><a href="#target_os">Operating System Features and Limitations</a> |
| <ul> |
| <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li> |
| <li>Linux, etc.</li> |
| </ul> |
| |
| </li> |
| </ul> |
| </li> |
| </ul> |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="intro">Introduction</h2> |
| <!-- ======================================================================= --> |
| |
| <p>The Clang Compiler is an open-source compiler for the C family of programming |
| languages, aiming to be the best in class implementation of these languages. |
| Clang builds on the LLVM optimizer and code generator, allowing it to provide |
| high-quality optimization and code generation support for many targets. For |
| more general information, please see the <a href="http://clang.llvm.org">Clang |
| Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p> |
| |
| <p>This document describes important notes about using Clang as a compiler for |
| an end-user, documenting the supported features, command line options, etc. If |
| you are interested in using Clang to build a tool that processes code, please |
| see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are |
| interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang |
| Static Analyzer</a>, please see its web page.</p> |
| |
| <p>Clang is designed to support the C family of programming languages, which |
| includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a |
| href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many |
| dialects of those. For language-specific information, please see the |
| corresponding language specific section:</p> |
| |
| <ul> |
| <li><a href="#c">C Language</a>: K&R C, ANSI C89, ISO C90, ISO C94 |
| (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li> |
| <li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus |
| variants depending on base language.</li> |
| <li><a href="#cxx">C++ Language Features</a></li> |
| <li><a href="#objcxx">Objective C++ Language</a></li> |
| </ul> |
| |
| <p>In addition to these base languages and their dialects, Clang supports a |
| broad variety of language extensions, which are documented in the corresponding |
| language section. These extensions are provided to be compatible with the GCC, |
| Microsoft, and other popular compilers as well as to improve functionality |
| through Clang-specific features. The Clang driver and language features are |
| intentionally designed to be as compatible with the GNU GCC compiler as |
| reasonably possible, easing migration from GCC to Clang. In most cases, code |
| "just works".</p> |
| |
| <p>In addition to language specific features, Clang has a variety of features |
| that depend on what CPU architecture or operating system is being compiled for. |
| Please see the <a href="target_features">Target-Specific Features and |
| Limitations</a> section for more details.</p> |
| |
| <p>The rest of the introduction introduces some basic <a |
| href="#terminology">compiler terminology</a> that is used throughout this manual |
| and contains a basic <a href="#basicusage">introduction to using Clang</a> |
| as a command line compiler.</p> |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="terminology">Terminology</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic, |
| optimizer</p> |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="basicusage">Basic Usage</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p>Intro to how to use a C compiler for newbies.</p> |
| <p> |
| compile + link |
| |
| compile then link |
| |
| debug info |
| |
| enabling optimizations |
| |
| picking a language to use, defaults to C99 by default. Autosenses based on |
| extension. |
| |
| using a makefile |
| </p> |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="commandline">Command Line Options</h2> |
| <!-- ======================================================================= --> |
| |
| <p> |
| This section is generally an index into other sections. It does not go into |
| depth on the ones that are covered by other sections. However, the first part |
| introduces the language selection and other high level options like -c, -g, etc. |
| </p> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p><b>-Werror</b>: Turn warnings into errors.</p> |
| <p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p> |
| <p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is |
| specified.</p> |
| <p><b>-Wfoo</b>: Enable warning foo</p> |
| <p><b>-Wno-foo</b>: Disable warning foo</p> |
| <p><b>-w</b>: Disable all warnings.</p> |
| <p><b>-pedantic</b>: Warn on language extensions.</p> |
| <p><b>-pedantic-errors</b>: Error on language extensions.</p> |
| <p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p> |
| |
| <!-- ================================================= --> |
| <h4 id="cl_diag_formatting">Formatting of Diagnostics</h4> |
| <!-- ================================================= --> |
| |
| <p>Clang aims to produce beautiful diagnostics by default, particularly for new |
| users that first come to Clang. However, different people have different |
| preferences, and sometimes Clang is driven by another program that wants to |
| parse simple and consistent output, not a person. For these cases, Clang |
| provides a wide range of options to control the exact output format of the |
| diagnostics that it generates.</p> |
| |
| <dl> |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in |
| diagnostic.</dt> |
| <dd>This option, which defaults to on, controls whether or not Clang prints the |
| column number of a diagnostic. For example, when this is enabled, Clang will |
| print something like:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| // |
| </pre> |
| |
| <p>When this is disabled, Clang will print "test.c:28: warning..." with no |
| column number.</p> |
| </dd> |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print |
| source file/line/column information in diagnostic.</dt> |
| <dd>This option, which defaults to on, controls whether or not Clang prints the |
| filename, line number and column number of a diagnostic. For example, |
| when this is enabled, Clang will print something like:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| // |
| </pre> |
| |
| <p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p> |
| </dd> |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source |
| line and ranges from source code in diagnostic.</dt> |
| <dd>This option, which defaults to on, controls whether or not Clang prints the |
| source line, source ranges, and caret when emitting a diagnostic. For example, |
| when this is enabled, Clang will print something like:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| // |
| </pre> |
| |
| <p>When this is disabled, Clang will just print:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| </pre> |
| |
| </dd> |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>: |
| Enable <tt>[-Woption]</tt> information in diagnostic line.</dt> |
| <dd>This option, which defaults to on, |
| controls whether or not Clang prints the associated <A |
| href="#cl_diag_warning_groups">warning group</a> option name when outputting |
| a warning diagnostic. For example, in this output:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| // |
| </pre> |
| |
| <p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing |
| the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the |
| diagnostic. This information tells you the flag needed to enable or disable the |
| diagnostic, either from the command line or through <a |
| href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd> |
| |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>: |
| Enable "FixIt" information in the diagnostics output.</dt> |
| <dd>This option, which defaults to on, controls whether or not Clang prints the |
| information on how to fix a specific diagnostic underneath it when it knows. |
| For example, in this output:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| // |
| </pre> |
| |
| <p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing |
| the "//" line at the end of the message. This information is useful for users |
| who may not understand what is wrong, but can be confusing for machine |
| parsing.</p> |
| </dd> |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_fdiagnostics-print-source-range-info"> |
| <b>-f[no-]diagnostics-print-source-range-info</b>: |
| Print machine parsable information about source ranges.</dt> |
| <dd>This option, which defaults to off, controls whether or not Clang prints |
| information about source ranges in a machine parsable format after the |
| file/line/column number information. The information is a simple sequence of |
| brace enclosed ranges, where each range lists the start and end line/column |
| locations. For example, in this output:</p> |
| |
| <pre> |
| exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float') |
| P = (P-42) + Gamma*4; |
| ~~~~~~ ^ ~~~~~~~ |
| </pre> |
| |
| <p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p> |
| </dd> |
| |
| |
| </dl> |
| |
| |
| |
| |
| <!-- ===================================================== --> |
| <h4 id="cl_diag_warning_groups">Individual Warning Groups</h4> |
| <!-- ===================================================== --> |
| |
| <p>TODO: Generate this from tblgen. Define one anchor per warning group.</p> |
| |
| |
| <dl> |
| |
| |
| <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - --> |
| <dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at |
| the end of a preprocessor directive.</dt> |
| <dd>This option, which defaults to on, enables warnings about extra tokens at |
| the end of preprocessor directives. For example:</p> |
| |
| <pre> |
| test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens] |
| #endif bad |
| ^ |
| </pre> |
| |
| <p>These extra tokens are not strictly conforming, and are usually best handled |
| by commenting them out.</p> |
| |
| <p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>, |
| and <a href="">-Wbaz</a>.</p> |
| </dd> |
| |
| </dl> |
| |
| <!-- ======================================================================= --> |
| <h2 id="general_features">Language and Target-Independent Features</h2> |
| <!-- ======================================================================= --> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="diagnostics">Controlling Errors and Warnings</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p>Clang provides a number of ways to control which code constructs cause it to |
| emit errors and warning messages, and how they are displayed to the console.</p> |
| |
| <h4>Controlling How Clang Displays Diagnostics</h4> |
| |
| <p>When Clang emits a diagnostic, it includes rich information in the output, |
| and gives you fine-grain control over which information is printed. Clang has |
| the ability to print this information, and these are the options that control |
| it:</p> |
| |
| <p> |
| <ol> |
| <li>A file/line/column indicator that shows exactly where the diagnostic occurs |
| in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a |
| href="#opt_fshow-source-location">-fshow-source-location</a>].</li> |
| <li>A categorization of the diagnostic as a note, warning, error, or fatal |
| error.</li> |
| <li>A text string that describes what the problem is.</li> |
| <li>An option that indicates how to control the diagnostic (for diagnostics that |
| support it) [<a |
| href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li> |
| <li>The line of source code that the issue occurs on, along with a caret and |
| ranges that indicate the important locations [<a |
| href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li> |
| <li>"FixIt" information, which is a concise explanation of how to fix the |
| problem (when Clang is certain it knows) [<a |
| href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li> |
| <li>A machine-parsable representation of the ranges involved (off by |
| default) [<a |
| href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li> |
| </ol></p> |
| |
| <p>For more information please see <a href="#cl_diag_formatting">Formatting of |
| Diagnostics</a>.</p> |
| |
| <h4>Controlling Which Diagnostics Clang Generates</h4> |
| |
| <p>mappings: ignore, note, warning, error, fatal</p> |
| |
| <p> |
| The two major classes are control from the command line and control via pragmas |
| in your code.</p> |
| |
| |
| <p>-W flags, -pedantic, etc</p> |
| |
| <p>pragma GCC diagnostic</p> |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="precompiledheaders">Precompiled Headers</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled |
| headers</a> are a general approach employed by many compilers to reduce |
| compilation time. The underlying motivation of the approach is that it is |
| common for the same (and often large) header files to be included by |
| multiple source files. Consequently, compile times can often be greatly improved |
| by caching some of the (redundant) work done by a compiler to process headers. |
| Precompiled header files, which represent one of many ways to implement |
| this optimization, are literally files that represent an on-disk cache that |
| contains the vital information necessary to reduce some of the work |
| needed to process a corresponding header file. While details of precompiled |
| headers vary between compilers, precompiled headers have been shown to be a |
| highly effective at speeding up program compilation on systems with very large |
| system headers (e.g., Mac OS/X).</p> |
| |
| <p>Clang supports an implementation of precompiled headers known as |
| <em>pre-tokenized headers</em> (PTH). Clang's pre-tokenized headers support most |
| of same interfaces as GCC's pre-compiled headers (as well as others) but are |
| completely different in their implementation. If you are interested in how |
| PTH is implemented, please see the <a href="PTHInternals.html">PTH Internals |
| document</a>.</p> |
| |
| <h4>Generating a PTH File</h4> |
| |
| <p>To generate a PTH file using Clang, one invokes Clang with |
| the <b><tt>-x <i><language></i>-header</tt></b> option. This mirrors the |
| interface in GCC for generating PCH files:</p> |
| |
| <pre> |
| $ gcc -x c-header test.h -o test.h.gch |
| $ clang -x c-header test.h -o test.h.pth |
| </pre> |
| |
| <h4>Using a PTH File</h4> |
| |
| <p>A PTH file can then be used as a prefix header when a |
| <b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p> |
| |
| <pre> |
| $ clang -include test.h test.c -o test |
| </pre> |
| |
| <p>The <tt>clang</tt> driver will first check if a PTH file for <tt>test.h</tt> |
| is available; if so, the contents of <tt>test.h</tt> (and the files it includes) |
| will be processed from the PTH file. Otherwise, Clang falls back to |
| directly processing the content of <tt>test.h</tt>. This mirrors the behavior of |
| GCC.</p> |
| |
| <p><b>NOTE:</b> Clang does <em>not</em> automatically used PTH files |
| for headers that are directly included within a source file. For example:</p> |
| |
| <pre> |
| $ clang -x c-header test.h -o test.h.pth |
| $ cat test.c |
| #include "test.h" |
| $ clang test.c -o test |
| </pre> |
| |
| <p>In this example, <tt>clang</tt> will not automatically use the PTH file for |
| <tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file |
| and not specified on the command line using <tt>-include</tt>.</p> |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="c">C Language Features</h2> |
| <!-- ======================================================================= --> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="c_incompatibilities">Intentional Incompatibilities with GCC</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p>No VLAs in structs.</p> |
| |
| |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="objc">Objective-C Language Features</h2> |
| <!-- ======================================================================= --> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <p>No cast of super, no lvalue casts.</p> |
| |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="cxx">C++ Language Features</h2> |
| <!-- ======================================================================= --> |
| |
| <p>At this point, Clang C++ is not generally useful. However, Clang C++ support |
| is under active development and is progressing rapidly. Please see the <a |
| href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or |
| ask on the mailing list about how you can help.</p> |
| |
| <p>Note that the clang driver will refuse to even try to use clang to compile |
| C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If |
| you really want to play with Clang's C++ support, please pass that flag. </p> |
| |
| <!-- ======================================================================= --> |
| <h2 id="objcxx">Objective C++ Language Features</h2> |
| <!-- ======================================================================= --> |
| |
| <p>At this point, Clang C++ support is not generally useful (and therefore, |
| neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for |
| more information.</p> |
| |
| <!-- ======================================================================= --> |
| <h2 id="target_features">Target-Specific Features and Limitations</h2> |
| <!-- ======================================================================= --> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="target_arch">CPU Architectures Features and Limitations</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <!-- ======================== --> |
| <h4 id="target_arch_x86">X86</h4> |
| <!-- ======================== --> |
| |
| |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| <h3 id="target_os">Operating System Features and Limitations</h3> |
| <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = --> |
| |
| <!-- ======================================= --> |
| <h4 id="target_os_darwin">Darwin (Mac OS/X)</h4> |
| <!-- ======================================= --> |
| |
| <p>No __thread support, 64-bit ObjC support requires SL tools.</p> |
| |
| </div> |
| </body> |
| </html> |