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134 lines
4.2 KiB
Plaintext
134 lines
4.2 KiB
Plaintext
This document present the STLport namespace schema and give additionnal
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information about how STLport replace the native C++ Standard library
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coming with your compiler.
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1. What is the STLport namespace ?
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As STLport is a C++ Standard library implementation the STLport namespace
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is 'std'. In normal use this is all you need to know and you can stop reading
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here.
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2. How does STLport replace native C++ Standard library ?
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STLport defines a macro 'std' that replaces all references of std in the
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user code by a different name. This technique has has some drawback but also
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advantages. The drawback is that you cannot declared Standard component like
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that:
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//foo.h
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namespace std
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{
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template <class _Tp>
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class allocator;
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}
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void f1(const std::allocator<int>&);
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//foo.cpp
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#include "foo.h"
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#include <memory>
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void f1(const std::allocator<int>& alloc)
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{
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//implementation
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}
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//bar.cpp
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#include "foo.h"
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#include <memory>
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int main(int, char**)
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{
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std::allocator<int> alloc;
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f1(alloc);
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}
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If you build this code you will surely have a compilation error as f1 is declared
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as taking a std::allocator parameter but you are calling it using an STLport allocator
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instance that is not in the std namespace. The good news is that this drawback is easy
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to detect as it will generate compilation error or at least link time error. The only
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workaround is to include an arbitrary Standard header before the allocator declaration.
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Good candidates for that are <utility> or <cerrno> as they are small headers. Including
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those headers will replace std with the STLport namespace.
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The advantage of this macro replacement is that we can customize the STLport namespace
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depending on the compilation options. For instance the STLport safe mode you can use by
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defining _STLP_DEBUG is not binary compatible with a normal debug build. To ensure that
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no one will ever build code without _STLP_DEBUG and link with STLport library built with
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this option the namespace is different so that it will generate link time error rather
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than random crashes during application execution.
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3. Why not having use namespace injection ?
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An other way to replace native Standard C++ library implementation would have been to
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use namespace injection:
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namespace std
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{
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using namespace stlport;
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}
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This solution has a first major drawback which is that STLport would be much more sensible
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to native headers. If you include a C++ native headers that indirectly define for instance
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the vector class it is going to conflict with the STLport vector definition.
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Moreover this solution just does not work for a very simple reason. The C++ Standard
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allows users to specialized some of the Standard algorithms. This specialization has to
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be done in the same namespace as the main template declaration:
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//In an STLport header:
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namespace stlport
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{
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template <class _Tp>
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struct less
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{
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bool operator () (const _Tp& x, const _Tp& y) const;
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};
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}
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//User code:
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struct MyStruct;
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namespace std
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{
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template <>
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struct less<MyStruct>
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{
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};
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}
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As you can see the specialization is not in the STLport less namespace and it
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won't be used in associative containers for instance.
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4. What is the STLport specific namespace ?
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The official STLport namespace is: stlport. Once again this is not the real namespace
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where all the Standard stuff are. As the real STLport namespace change depending on compilation
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options you cannot use it directly. So stlport is an alias of the real STLport namespace.
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5. What are the other STLport namespaces ?
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Those names are given for information purpose and should never be used in any user code. The
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default STLport namespace is: stlp_std. Here is the list of the customized namespaces:
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- stlpd_std : when _STLP_DEBUG is defined
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- stlpx_std : when you use STLport as a shared library linked to the static version of the native
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runtime or when you build the static STLport library linked with the dynamic version. This option
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is only supported by a limited number of compilers.
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- stlpmtx_std : when building STLport as not thread safe.
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You can also have combination of those extension like stlpdxmtx_std or stlpdmtx_std...
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There is also an other STLport namespace for STLport internal functions or struct/class: priv.
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namespace stlport
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{
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namespace priv
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{
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}
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}
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