IT. Expert System.

Composes a string with the same text that would be printed if format was used on printf, but using the elements in the variable argument list identified by arg instead of additional function arguments and storing the resulting content as a C string in the buffer pointed by s (taking n as the maximum buffer capacity to fill).

Syntax:

int vsnprintf (char * s, size_t n, const char * format, va_list arg );

Example:

#include 
#include 

void PrintFError ( const char * format, ... )
{
  char buffer[256];
  va_list args;
  va_start (args, format);
  vsnprintf (buffer,256,format, args);
  perror (buffer);
  va_end (args);
}

int main ()
{
   FILE * pFile;
   char szFileName[]="myfile.txt";

   pFile = fopen (szFileName,"r");
   if (pFile == NULL)
     PrintFError ("Error opening '%s'",szFileName);
   else
   {
     // file successfully open
     fclose (pFile);
   }
   return 0;
}

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