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<title>Portability Hints: Microsoft Visual C++ 6.0 SP4</title>
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<body bgcolor="#FFFFFF" text="#000000">
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<table border="1" bgcolor="#007F7F" cellpadding="2" summary="">
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<tr>
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<td bgcolor="#FFFFFF"><img src="../boost.png" alt=
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<td><a href="../index.htm"><font face="Arial,Helvetica" color=
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"#FFFFFF"><big>More</big></font></a></td>
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</table>
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<h1>Portability Hints: Microsoft Visual C++ 6.0 SP4</h1>
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<p>Similar to the <a href="borland_cpp.html">portability hints for Borland
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C++</a>, this page provides hints on some language features of the
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Microsoft Visual C++ version 6.0 service pack 4 compiler. A list of
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acknowledged deficiencies can be found at the <a href=
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"http://support.microsoft.com/support/kb/articles/q243/4/51.asp">Microsoft
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support site</a>.</p>
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<p>Each entry in the following list describes a particular issue, complete
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with sample source code to demonstrate the effect. Most sample code herein
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has been verified to compile with gcc 2.95.2 and Comeau C++ 4.2.44.</p>
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<h2>Preprocessor symbol</h2>
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<p>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 also
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define this symbol, boost provides the symbol <code>BOOST_MSVC</code>,
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which is defined in <a href="../boost/config.hpp">boost/config.hpp</a> to
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the value of _MSC_VER if and only if the compiler is really Microsoft
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Visual C++. The following table lists some known values.</p>
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<table border="1" summary="">
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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 SP6)</td>
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<td>1200</td>
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</tr>
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<tr>
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<td>Microsoft embedded Visual C++ 4.0</td>
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<td>1200-1202 (cross compilers)</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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<p>Chaining <code>using</code>-declarations does not work.</p>
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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 instantiation</h3>
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<p>Trying to explicitly instantiate a function template leads to the wrong
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function being called silently.</p>
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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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<p>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.</p>
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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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<p><strong>Workaround:</strong> Enclose the offending <code>for</code>
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loops in another pair of curly braces.</p>
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<p>Another possible workaround (brought to my attention by Vesa Karvonen)
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is this:</p>
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<pre>
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#ifndef for
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#define for if (0) {} else for
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#endif
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</pre>
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<p>Note that platform-specific inline functions in included headers might
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depend on the old-style <code>for</code> scoping.</p>
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<h3>[inclass-member-init] In-class member initialization</h3>
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<p>In-class member initialization, required to implement a
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Standard-conforming <code>std::numeric_limits</code> template, does not
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work.</p>
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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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<p><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 the
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value out-of-line (which allows for the correct type, but prohibits using
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the constant in compile-time constant expressions). See <a href=
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"int_const_guidelines.htm">Coding Guidelines for Integral Constant
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Expressions</a> for guidelines how to define member constants portably in
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boost libraries.</p>
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<h3>[koenig-lookup] Argument-dependent lookup</h3>
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<p>Argument-dependent lookup, also called Koenig lookup, works for
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overloaded operators, but not for ordinary functions. No additional
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namespaces induced from the argument types seem to be considered.</p>
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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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<p>A Template cannot be declared a friend of a class.</p>
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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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<p>Defining member templates outside their enclosing class does not
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work.</p>
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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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<p><strong>Workaround:</strong> Define member templates in-line within
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their enclosing class.</p>
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<h3>[partial-spec] Partial specialization</h3>
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<p>Partial specialization of class templates does not work.</p>
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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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<p><strong>Workaround:</strong> In some situations where interface does not
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matter, class member templates can simulate partial specialization.</p>
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<h3>[template-value] Dependent template value parameters</h3>
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<p>Template value parameters whose type depends on a previous template
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parameter provoke an internal compiler error if the correct syntax (with
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"typename") is used.</p>
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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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<p><strong>Workaround:</strong> Leave off the "typename" keyword. That
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makes the program non-conforming, though.</p>
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<h3>[wchar_t] <code>wchar_t</code> is not built-in</h3>
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<p>The type <code>wchar_t</code> is not a built-in type.</p>
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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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<p><strong>Workaround:</strong> When using Microsoft Visual C++, the header
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<a href="../boost/config.hpp">boost/config.hpp</a> includes
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<code><cstddef></code>, which defines <code>wchar_t</code> as a
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typedef for <code>unsigned short</code>. Note that this means that the
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compiler does not regard <code>wchar_t</code> and <code>unsigned
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short</code> as distinct types, as is required by the standard, and so
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ambiguities may emanate 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.</p>
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<h3>[delete-const-pointer] Deleting <code>const X *</code> does not
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work</h3>
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<p>Trying to delete a pointer to a cv-qualified type gives an error:</p>
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<pre>
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void f()
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{
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const int *p = new int(5);
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delete p; // C2664: cannot convert from "const int *" to "void *"
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}
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</pre>
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<p><strong>Workaround:</strong> Define the function</p>
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<pre>
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inline void operator delete(const void *p) throw()
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{ operator delete(const_cast<void*>(p)); }
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</pre>
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<p>and similar functions for the other cv-qualifier combinations, for
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operator delete[], and for the <code>std::nothrow</code> variants.</p>
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<h2>Standard Library</h2>
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<h3>[clib-namespace] C library names in global namespace instead of
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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>
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<p><b>Workaround:</b> The header <a href=
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"../libs/config/config.htm">boost/config.hpp</a> will define
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BOOST_NO_STDC_NAMESPACE. It can be used as follows:</p>
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<pre>
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# ifdef BOOST_NO_STDC_NAMESPACE
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namespace std { using ::abs; using ::fabs; }
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# endif
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</pre>
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<p>Because std::size_t and std::ptrdiff_t are so commonly used, the
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workaround for these is already provided in boost/config.hpp.</p>
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<hr>
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<p><a href="http://validator.w3.org/check?uri=referer"><img border="0" src=
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"http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01 Transitional"
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height="31" width="88"></a></p>
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<p>Revised
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<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->04 December, 2006<!--webbot bot="Timestamp" endspan i-checksum="38514" --></p>
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<p><i>Copyright © 2001-2002 <a href="../people/jens_maurer.htm">Jens
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Maurer</a></i></p>
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<p><i>Distributed under the Boost Software License, Version 1.0. (See
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accompanying file <a href="../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or copy
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at <a href=
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"http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</a>)</i></p>
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</body>
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