Re: Macros with G++

[Guy Harrison]

Michael Meier wrote:

> Hi,
> 
> I'm not sure weather this is a compiler error or sonething different. The
> code:
> 
> #include <stdio.h>
> #include <wchar.h>
> 
> //#define WIDE(x) L#x doesnt work

"Stringify"...

L#x = "x"

> #define WIDE(x) L##x

Token Pasting...

L##x = Lx

> int main( void )
> {
>    //wchar_t test = WIDE( Hello World ); doesnt work
>     wchar_t* test = WIDE( "Hello World" );
>     return 4;
> }
> 
> The question is why the first approach doesn't work. g++ complains that L
> has not been defined. One hash should expand the variable and put it into
> quotes whereas two hashes just expand the variable. It works with two but
> not with one hash. Any explanation is welcome!

Your second version is the correct approach. Something like this...

#if defined(UNICODE)
#       define  APP_L(x)        L##x
#       define  APP_C           wchar_t
#else
#       define  APP_L(x)        x
#       define  APP_C           char
#endif

const APP_C     s[]     =APP_L("ook");
const APP_C     c       =APP_L('a');

It's easier in C++ ...

<some app global header>
typedef std::basic_ostream< APP_C > AppOs;

typedef enum {
 APP_COUT,APP_CERR,APP_CLOG
}       APP_LOG;

AppOS & AppLog(APP_LOG =APP_CERR);
</some app global header>

<some compilation unit>
#if defined(UNICODE)
#       define  APP_COUT        std::wcout
        ...
#else
#       define  APP_COUT        std::cout
        ...
#endif

AppOS &
AppLog(APP_LOG x)
{
 switch (x)
  case APP_COUT: return APP_COUT;
  ...
 }
}
</some compilation unit>

#include "some global header"
int main()
{
 AppLog() << APP_L("at last!\n");
 return 0;
}

You'll need a unicode capable terminal. In the case of windows, this is one
area where it's much easier (eg: filenames etc). Doing it transparently in
C results in macro hell, re: windows again - winapi headers!