2009-04-20 12:23:09 +08:00
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<title>Clang Compiler User's Manual</title>
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<div id="content">
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<h1>Clang Compiler User's Manual</h1>
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<ul>
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<li><a href="#intro">Introduction</a>
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<ul>
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<li><a href="#terminology">Terminology</a></li>
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<li><a href="#basicusage">Basic Usage</a></li>
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</ul>
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</li>
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<li><a href="#commandline">Command Line Options</a></li>
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<li><a href="#general_features">Language and Target-Independent Features</a>
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<ul>
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<li><a href="#diagnostics">Controlling Errors and Warnings</a></li>
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<li><a href="#precompiledheaders">Precompiled Headers</a></li>
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</ul>
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</li>
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<li><a href="#c">C Language Features</a>
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<ul>
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<!-- <li><a href="#pragmas">Pragmas Supported</a></li> -->
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<li><a href="#c_extensions">C Extensions Supported</a></li>
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<li><a href="#c_incompatibilities">Intentional Incompatibilities with
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GCC</a></li>
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</ul>
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</li>
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<li><a href="#objc">Objective-C Language Features</a>
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<ul>
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<li><a href="#objc_incompatibilities">Intentional Incompatibilities with
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GCC</a></li>
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</ul>
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</li>
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<li><a href="#cxx">C++ Language Features</a>
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<ul>
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<li>...</li>
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</ul>
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</li>
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<li><a href="#objcxx">Objective C++ Language Features</a>
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<ul>
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<li>...</li>
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</ul>
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</li>
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<li><a href="#target_features">Target-Specific Features and Limitations</a>
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<ul>
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<li><a href="#target_arch">CPU Architectures Features and Limitations</a>
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<ul>
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<li><a href="#target_arch_x86">X86</a></li>
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<li>PPC</li>
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<li>ARM</li>
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</ul>
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</li>
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<li><a href="#target_os">Operating System Features and Limitations</a>
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<ul>
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<li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
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<li>Linux, etc.</li>
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</ul>
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</li>
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</ul>
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</li>
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</ul>
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<!-- ======================================================================= -->
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<h2 id="intro">Introduction</h2>
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<!-- ======================================================================= -->
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<p>The Clang Compiler is an open-source compiler for the C family of programming
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languages, aiming to be the best in class implementation of these languages.
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Clang builds on the LLVM optimizer and code generator, allowing it to provide
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high-quality optimization and code generation support for many targets. For
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more general information, please see the <a href="http://clang.llvm.org">Clang
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Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
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<p>This document describes important notes about using Clang as a compiler for
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an end-user, documenting the supported features, command line options, etc. If
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you are interested in using Clang to build a tool that processes code, please
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see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
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interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
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Static Analyzer</a>, please see its web page.</p>
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<p>Clang is designed to support the C family of programming languages, which
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includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
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href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
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dialects of those. For language-specific information, please see the
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corresponding language specific section:</p>
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<ul>
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<li><a href="#c">C Language</a>: K&R C, ANSI C89, ISO C90, ISO C94
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(C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
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<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
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variants depending on base language.</li>
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<li><a href="#cxx">C++ Language Features</a></li>
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<li><a href="#objcxx">Objective C++ Language</a></li>
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</ul>
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<p>In addition to these base languages and their dialects, Clang supports a
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broad variety of language extensions, which are documented in the corresponding
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language section. These extensions are provided to be compatible with the GCC,
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Microsoft, and other popular compilers as well as to improve functionality
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through Clang-specific features. The Clang driver and language features are
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intentionally designed to be as compatible with the GNU GCC compiler as
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reasonably possible, easing migration from GCC to Clang. In most cases, code
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"just works".</p>
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<p>In addition to language specific features, Clang has a variety of features
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that depend on what CPU architecture or operating system is being compiled for.
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Please see the <a href="target_features">Target-Specific Features and
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Limitations</a> section for more details.</p>
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<p>The rest of the introduction introduces some basic <a
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href="#terminology">compiler terminology</a> that is used throughout this manual
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and contains a basic <a href="#basicusage">introduction to using Clang</a>
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as a command line compiler.</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="terminology">Terminology</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
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optimizer</p>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="basicusage">Basic Usage</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>Intro to how to use a C compiler for newbies.</p>
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<p>
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compile + link
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compile then link
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debug info
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enabling optimizations
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picking a language to use, defaults to C99 by default. Autosenses based on
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extension.
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using a makefile
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</p>
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<!-- ======================================================================= -->
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<h2 id="commandline">Command Line Options</h2>
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<!-- ======================================================================= -->
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<p>
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This section is generally an index into other sections. It does not go into
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depth on most. However, the first part introduces the language selection and
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other high level options like -c, -g, etc.
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</p>
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<!-- ======================================================================= -->
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<h2 id="general_features">Language and Target-Independent Features</h2>
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<!-- ======================================================================= -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="diagnostics">Controlling Errors and Warnings</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="precompiledheaders">Precompiled Headers</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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2009-04-20 12:37:38 +08:00
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<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
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headers</a> are a general approach employed by many compilers to reduce
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compilation time. The underlying motivation of the approach is that it is
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common for the same (and often large) header files to be included by
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multiple source files. Consequently, compile times can often be greatly improved
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by caching some of the (redundant) work done by a compiler to process headers.
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Precompiled header files, which represent one of many ways to implement
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this optimization, are literally files that represent an on-disk cache that
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contains the vital information necessary to reduce some of the work
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needed to process a corresponding header file. While details of precompiled
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headers vary between compilers, precompiled headers have been shown to be a
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highly effective at speeding up program compilation on systems with very large
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system headers (e.g., Mac OS/X).</p>
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<p>Clang supports an implementation of precompiled headers known as
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<em>pre-tokenized headers</em> (PTH). Clang's pre-tokenized headers support most
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of same interfaces as GCC's pre-compiled headers (as well as others) but are
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completely different in their implementation. If you are interested in how
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PTH is implemented, please see the <a href="PTHInternals.html">PTH Internals
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document</a>.</p>
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<h4>Generating a PTH File</h4>
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<p>To generate a PTH file using Clang, one invokes Clang with
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the <b><tt>-x <i><language></i>-header</tt></b> option. This mirrors the
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interface in GCC for generating PCH files:</p>
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<pre>
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$ gcc -x c-header test.h -o test.h.gch
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$ clang -x c-header test.h -o test.h.pth
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</pre>
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<h4>Using a PTH File</h4>
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<p>A PTH file can then be used as a prefix header when a
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<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
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<pre>
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$ clang -include test.h test.c -o test
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</pre>
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<p>The <tt>clang</tt> driver will first check if a PTH file for <tt>test.h</tt>
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is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
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will be processed from the PTH file. Otherwise, Clang falls back to
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directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
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GCC.</p>
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<p><b>NOTE:</b> Clang does <em>not</em> automatically used PTH files
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for headers that are directly included within a source file. For example:</p>
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<pre>
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$ clang -x c-header test.h -o test.h.pth
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$ cat test.c
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#include "test.h"
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$ clang test.c -o test
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</pre>
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<p>In this example, <tt>clang</tt> will not automatically use the PTH file for
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<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
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and not specified on the command line using <tt>-include</tt>.</p>
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2009-04-20 12:23:09 +08:00
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<!-- ======================================================================= -->
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<h2 id="c">C Language Features</h2>
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<!-- ======================================================================= -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="c_incompatibilities">Intentional Incompatibilities with GCC</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>No VLAs in structs.</p>
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<!-- ======================================================================= -->
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<h2 id="objc">Objective-C Language Features</h2>
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<!-- ======================================================================= -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="objc_incompatibilities">Intentional Incompatibilities with GCC</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<p>No cast of super, no lvalue casts.</p>
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<!-- ======================================================================= -->
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<h2 id="cxx">C++ Language Features</h2>
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<!-- ======================================================================= -->
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<p>At this point, Clang C++ is not generally useful. However, Clang C++ support
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is under active development and is progressing rapidly. Please see the <a
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href="http://clang.llvm.org/cxx_status.html">C++ Status</a> page for details or
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ask on the mailing list about how you can help.</p>
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<p>Note that the clang driver will refuse to even try to use clang to compile
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C++ code unless you pass the <tt>-ccc-clang-cxx</tt> option to the driver. If
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you really want to play with Clang's C++ support, please pass that flag. </p>
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<!-- ======================================================================= -->
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<h2 id="objcxx">Objective C++ Language Features</h2>
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<!-- ======================================================================= -->
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<p>At this point, Clang C++ support is not generally useful (and therefore,
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neither is Objective-C++). Please see the <a href="#cxx">C++ section</a> for
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more information.</p>
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<!-- ======================================================================= -->
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<h2 id="target_features">Target-Specific Features and Limitations</h2>
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<!-- ======================================================================= -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
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<!-- ======================== -->
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<h4 id="target_arch_x86">X86</h4>
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<!-- ======================== -->
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<h3 id="target_os">Operating System Features and Limitations</h3>
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<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
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<!-- ======================================= -->
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<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
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<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
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</div>
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</body>
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</html>
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