Randy Bowen wrote: >> A disappointing aspect of this in regards to MSVC 7.0+ is >> that there is no preprocessor macro ( as of 7.0, I haven't >> checked 7.1 yet ) which MSVC defines for distinguishing >> native C++ wide character from the previous typedef for >> wchar_t. > > The MS-specific macro _NATIVE_WCHAR_T_DEFINED indicates the presence > of > the native type in MSVC 7.0+. However, use of this can cause a number > of problems with existing MS libraries (and especially anything that > deals with COM).
The documentation is very confusing regarding this. First we have under Predefined Macros: "_WCHAR_T_DEFINED and _NATIVE_WCHAR_T_DEFINED Defined when wchar_t is defined. Typically, wchar_t is defined when you use /Zc:wchar_t or when typedef unsigned short wchar_t; is executed in code." which implies that both the macros above are defined in both cases. Next we have under the compiler switch "/Zc:wchar_t (wchar_t Is Native Type)": "When /Zc:wchar_t is specified, _WCHAR_T_DEFINED and _NATIVE_WCHAR_T_DEFINED symbols are defined; see Predefined Macros for more information." which simply reiterates the first part of the previous topic. Testing this out, both VC++ 7.0 and VC++ 7.1 yield the same result which confirms what you have written above. When the /Zc:wchar_t switch is used, both of the above macros are defined. When the /Zc:wchar_t is not used, only the _WCHAR_T_DEFINED macro is defined. So I was definitely wrong in thinking that there was no way to test for the difference. Perhaps the previous documentation which I read didn't explain the _NATIVE_WCHAR_T_DEFINED macro or perhaps I just missed it. But this is good for Boost. Now there is a way to determine whether which of the wchar_t types in VC++ are being used at compile time. My suggestion for Boost is that it use library implementors use this in order to alert the end-user at compile time that a particular usage of wchar_t is not supported, or use it to correctly link in the correct version of the library when both are supported. For VC++, the #pragma comment(lib,"SomeLib") specifies the name of the library to link, either import or static. I know John Maddock does this in Regex++ but the general usage for our wchar_t, reiterated here, would be: #if defined(_NATIVE_WCHAR_T_DEFINED) #pragma comment(lib,"NativeWchartVersion.lib" #elif defined(_WCHAR_T_DEFINED) #pragma comment(lib,"VCWchartVersion.lib") #endif Of course I expect Boost may want to create BOOST_ macros for these VC++ specific macros in the correct configuration file and use them instead, but one gets the general idea from this. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
