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<html>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<title>Portability Hints: Microsoft Visual C++ 6.0 SP4</title>
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<table border="1" bgcolor="#007F7F" cellpadding="2">
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<tr>
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<td bgcolor="#FFFFFF"><img src="../c++boost.gif" alt="c++boost.gif (8819 bytes)" width="277" height="86"></td>
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<td><a href="../index.htm"><font face="Arial,Helvetica" color="#FFFFFF"><big>Home</big></font></a></td>
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<td><a href="../libs/libraries.htm"><font face="Arial,Helvetica" color="#FFFFFF"><big>Libraries</big></font></a></td>
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<td><a href="../people/people.htm"><font face="Arial,Helvetica" color="#FFFFFF"><big>People</big></font></a></td>
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<td><a href="faq.htm"><font face="Arial,Helvetica" color="#FFFFFF"><big>FAQ</big></font></a></td>
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<td><a href="index.htm"><font face="Arial,Helvetica" color="#FFFFFF"><big>More</big></font></a></td>
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</table>
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<p>
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<h1>Portability Hints: Microsoft Visual C++ 6.0 SP4</h1>
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Similar to the
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<a href="borland_cpp.html">portability hints for Borland C++</a>,
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this page provides hints on some language features of the Microsoft Visual C++
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version 6.0 service pack 4 compiler. A list of
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acknowledged deficiencies can be found at the
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<a href="http://support.microsoft.com/support/kb/articles/q243/4/51.asp">Microsoft support site</a>.
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<p>
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Each entry in the following list describes a particular issue,
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complete with sample source code to demonstrate the effect.
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Most sample code herein has been verified to compile with gcc 2.95.2
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and Comeau C++ 4.2.44.
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<h2>Preprocessor symbol</h2>
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The preprocessor symbol <code>_MSC_VER</code> is defined for all
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Microsoft C++ compilers. Its value is the internal version number of the
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compiler interpreted as a decimal number. Since a few other compilers
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also define this symbol, boost provides the symbol
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<code>BOOST_MSVC</code>, which is defined in
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<a href="../boost/config.hpp">boost/config.hpp</a>
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to the value of _MSC_VER if and only if the compiler is really
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Microsoft Visual C++.
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The following table lists some known values.
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<p>
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<table border="1">
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<tr>
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<th>Compiler</th>
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<th><code>BOOST_MSVC</code> value</th>
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</tr>
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<tr>
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<td>Microsoft Visual C++ 6.0 (up to SP4)</td>
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<td>1200</td>
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</tr>
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</table>
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<h2>Core Language</h2>
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<h3>[chained using] Chaining <code>using</code>-declarations</h3>
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Chaining <code>using</code>-declarations does not work.
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<pre>
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void f();
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namespace N {
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using ::f;
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}
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void g()
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{
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using N::f; // C2873: 'f': the symbol cannot be used in a using-declaration
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}
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</pre>
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<h3>[explicit-instantiation] Explicit function template
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instantiation</h3>
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Trying to explicitly instantiate a function template leads to the
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wrong function being called silently.
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<pre>
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#include <stdio.h>
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template<class T>
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void f()
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{
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printf("%d\n", sizeof(T));
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}
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int main()
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{
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f<double>(); // output: "1"
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f<char>(); // output: "1"
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return 0;
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}
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</pre>
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<h3>[for-scoping] Scopes of definitions in for-loops</h3>
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The scope of variable definitions in <code>for</code> loops should be
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local to the loop's body, but it is instead local to the enclosing
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block.
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<pre>
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int main()
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{
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for(int i = 0; i < 5; ++i)
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;
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for(int i = 0; i < 5; ++i) // C2374: 'i': Redefinition; multiple initialization
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;
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return 0;
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}
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</pre>
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<strong>Workaround:</strong> Enclose the offending <code>for</code>
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loops in another pair of curly braces.
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<h3>[inclass-member-init] In-class member initialization</h3>
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In-class member initialization, required to implement a
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Standard-conforming <code>std::numeric_limits</code> template, does
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not work.
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<pre>
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struct A
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{
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static const int i = 5; // "invalid syntax for pure virtual method"
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};
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</pre>
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<strong>Workaround:</strong> Either use an enum (which has incorrect
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type, but can be used in compile-time constant expressions), or define
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the value out-of-line (which allows for the correct type, but prohibits
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using the constant in compile-time constant expressions). See
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<a href="int_const_guidelines.htm">Coding Guidelines for Integral Constant Expressions</a>
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for guidelines how to define member constants portably in boost
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libraries.
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<h3>[koenig-lookup] Argument-dependent lookup</h3>
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Argument-dependent lookup, also called Koenig lookup, works for
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overloaded operators, but not for ordinary functions. No
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additional namespaces induced from the argument types seem to be
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considered.
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<pre>
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namespace N {
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struct A {};
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void f(A);
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}
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void g()
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{
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N::A a;
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f(a); // 'f': undeclared identifier
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}
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</pre>
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<h3>[template-friend] Templates as friends</h3>
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A Template cannot be declared a friend of a class.
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<pre>
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template<class T>
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struct A {};
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struct B
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{
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template<class T>
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friend struct A; // "syntax error"
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};
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</pre>
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<h3>[member-template-outofline] Out-of-line definitions of member
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templates</h3>
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Defining member templates outside their enclosing class does not work.
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<pre>
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template<class T>
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struct A
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{
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template<class U>
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void f();
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};
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template<class T>
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template<class U> // "syntax error"
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void A<T>::f() // "T: undeclared identifier"
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{
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}
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</pre>
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<strong>Workaround:</strong> Define member templates in-line within
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their enclosing class.
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<h3>[partial-spec] Partial specialization</h3>
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Partial specialization of class templates does not work.
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<pre>
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template<class T>
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struct A {};
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template<class T>
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struct B {};
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template<class T>
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struct A<B<T> > {}; // template class was already defined as a non-template
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</pre>
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<strong>Workaround:</strong> In some situations where interface
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does not matter, class member templates can simulate partial
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specialization.
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<h3>[template-value] Dependent template value parameters</h3>
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Template value parameters whose type depends on a previous template
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parameter provoke an internal compiler error if the correct syntax
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(with "typename") is used.
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<pre>
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template<class T, typename T::result_type> // C1001: INTERNAL COMPILER ERROR: msc1.cpp, line 1794
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struct B {};
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// (omit "typename" and it compiles)
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</pre>
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<strong>Workaround:</strong> Leave off the "typename" keyword. That makes
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the program non-conforming, though.
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<h3>[wchar_t] <code>wchar_t</code> is not built-in</h3>
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The type <code>wchar_t</code> is not a built-in type.
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<pre>
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wchar_t x; // "missing storage class or type identifier"
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</pre>
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<strong>Workaround:</strong> When using Microsoft Visual C++, the
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header
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<a href="../boost/config.hpp">boost/config.hpp</a>
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includes <code><cstddef></code>, which defines
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<code>wchar_t</code> as a typedef for <code>unsigned
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short</code>. Note that this means that the compiler does not regard
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<code>wchar_t</code> and <code>unsigned short</code> as distinct
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types, as is required by the standard, and so ambiguities may emanate
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when overloading on <code>wchar_t</code>. The macro
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<code>BOOST_NO_INTRINSIC_WCHAR_T</code> is defined in this situation.
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<h2>
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Standard Library</h2>
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<h3>[clib-namespace] C library names in global namespace instead of std</h3>
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<p>Library names from the <c...> headers are in the global namespace
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instead of namespace std.<p><b>Workaround:</b> The header <a href="../libs/config/index.htm">boost/config.hpp</a>
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will define BOOST_NO_STDC_NAMESPACE. It can be used as follows:
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<pre># ifdef BOOST_NO_STDC_NAMESPACE
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namespace std { using ::abs; using ::fabs; }
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# endif</pre>
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<p>Because std::size_t and std::ptrdiff_t are so commonly used, the workaround
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for these is already provided in boost/config.hpp.<p>
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<hr>
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2001-05-04 <a href="../people/jens_maurer.htm">Jens Maurer</a>
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</body>
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</html>
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