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< title > "libc++abi" C++ Standard Library Support< / title >
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< a href = "https://llvm.org/" > LLVM Home< / a >
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< label > libc++abi Info< / label >
< a href = "/index.html" > About< / a >
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< label > Quick Links< / label >
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< a href = "https://libcxx.llvm.org/" > libc++< / a >
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< a href = "https://lists.llvm.org/mailman/listinfo/libcxx-dev" > libcxx-dev< / a >
< a href = "https://lists.llvm.org/mailman/listinfo/libcxx-commits" > libcxx-commits< / a >
< a href = "https://bugs.llvm.org/" > Bug Reports< / a >
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< a href = "https://github.com/llvm/llvm-project/tree/main/libcxxabi/" > Browse Sources< / a >
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< h1 > "libc++abi" C++ Standard Library Support< / h1 >
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< p > libc++abi is a new implementation of low level support for a standard
C++ library.< / p >
< p > All of the code in libc++abi is < a
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href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed< / a >
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under the MIT license and the UIUC License (a BSD-like license).< / p >
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< h2 id = "goals" > Features and Goals< / h2 >
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< ul >
< li > Correctness as defined by the C++11 standard.< / li >
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< li > Provide a portable sublayer to ease the porting of < a href = "https://libcxx.llvm.org/" > libc++< / a > < / li >
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< li > On Mac OS X, be ABI compatible with the existing low-level support.< / li >
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< / ul >
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< h2 id = "requirements" > Platform Support< / h2 >
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< p > libc++abi is known to work on the following platforms, using clang.< / p >
< ul >
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< li > Darwin< / li >
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< / ul >
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< h2 id = "dir-structure" > Current Status< / h2 >
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< p > libc++abi is complete. < a href = "spec.html" > Here< / a > is a
list of functionality.< / p >
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< h2 > Get it and get involved!< / h2 >
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< p > To check out the code (including llvm and others), use:< / p >
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< ul >
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< li > < code > git clone https://github.com/llvm/llvm-project.git< / code > < / li >
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< / ul >
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< p > To build:< / p >
< ul >
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< li > < code > cd llvm-project< / code > < / li >
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< li > < code > mkdir build & & cd build< / code > < / li >
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< li > < code > cmake -DLLVM_ENABLE_PROJECTS=libcxxabi ../llvm # on linux you may need to specify -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++< / code > < / li >
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< li > < code > make< / code > < / li >
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< p > To do a standalone build:< / p >
< ul >
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< li >
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Check out the source tree. This includes the other subprojects, but you'll only use the libcxxabi part.
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< / li >
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< li > < code > cd llvm-project< / code > < / li >
< li > < code > mkdir build-libcxxabi & & cd build-libcxxabi< / code > < / li >
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< li > < code > cmake ../libcxxabi # on linux you may need -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++< / code > < / li >
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< li > < code > make< / code > < / li >
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< p > By default CMake uses < code > llvm-config< / code > to locate the required
LLVM sources. If CMake cannot find < code > llvm-config< / code > then you must
configure CMake using either of the following options.
< / p >
< ul >
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< li > < code > -DLLVM_CONFIG_PATH=path/to/llvm-config< / code > < / li >
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< li > < code > -DLLVM_PATH=path/to/llvm-source-root< / code > < / li >
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< / p >
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< p > To run the tests:< / p >
< ul >
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< li > < code > make check-cxxabi< / code > < / li >
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< / ul >
< p > Note: in a standalone build, the system's libc++ will be used for tests. If
the system's libc++ was statically linked against libc++abi (or linked against
a different ABI library), this may interfere with test results.< / p >
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< p > Send discussions to the
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(< a href = "https://lists.llvm.org/mailman/listinfo/libcxx-dev" > libcxx-dev mailing list< / a > ).< / p >
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< h2 > Frequently asked questions< / h2 >
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< p > Q: Why are the destructors for the standard exception classes defined in libc++abi?
They're just empty, can't they be defined inline?< / p >
< p > A: The destructors for them live in libc++abi because they are "key" functions.
The Itanium ABI describes a "key" function as the first virtual declared.
And wherever the key function is defined, that is where the < code > type_info< / code > gets defined.
And in libc++ types are the same type if and only if they have the same < code > type_info< / code >
(as in there must be only one type info per type in the entire application).
And on OS X, libstdc++ and libc++ share these exception types.
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So to be able to throw in one dylib and catch in another (a < code > std::exception< / code > for example),
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there must be only one < code > std::exception type_info< / code > in the entire app.
That typeinfo gets laid down beside < code > ~exception()< / code > in libc++abi (for both libstdc++ and libc++).< / p >
< p > --Howard Hinnant< / p >
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