Question

Having implemented CLogClass to make decent logging I also defined macro, but it works only with one parameter…

class CLogClass {  public:        static void DoLog(LPCTSTR sMessage, ...); }; #define DebugLog(sMessage, x) ClogClass::DoLog(__FILE__, __LINE__, sMessage, x) 

Well, it fails when called with more than 2 parameters 🙁 … Is it possible at all to avoid it? Can it be translated to templates somehow?

EDIT: Variadic macros were introduced in VS 2005 (But i’m currently in VS 2003…). Any advices?

Answer 1

You could have a MYLOG macro returning a custom functor object which takes a variable number of arguments.

#include <string> #include <cstdarg>  struct CLogObject {    void operator()( const char* pFormat, ... ) const {     printf( '[%s:%d] ', filename.c_str(), linenumber );     va_list args;     va_start( args, pFormat );     vfprintf( stderr, pFormat, args );     va_end( args );   }    CLogObject( std::string filename, const int linenumber )     : filename( filename ), linenumber( linenumber )   {}   std::string filename;   int linenumber; };  #define MYLOG CLogObject( __FILE__, __LINE__ )   int _tmain(int argc, _TCHAR* argv[]) {    MYLOG( '%s, %d', 'string', 5 );   return 0; } 

Note that it’s not so hard to step over to the type-safe variant touched by this answer: you don’t need any variadic arguments due to the chaining effect of operator<<.

struct CTSLogObject {    template< typename T >   std::ostream& operator<<( const T& t ) const {     return std::cout << '[' << filename << ':' << linenumber << '] ';   }    CTSLogObject( std::string filename, const int linenumber )     : filename( filename ), linenumber( linenumber )   {}   std::string filename;   int linenumber; }; #define typesafelog CTSLogObject( __FILE__, __LINE__ )  int _tmain(int argc, _TCHAR* argv[]) {   typesafelog << 'typesafe' << ', ' << 5 << std::endl;   return 0; }