#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>

char *fmtmsg( char *format, ... )
  {
    char    *msgbuf;
    int     len;
    va_list arglist;

    va_start( arglist, format );
    len = vsnprintf( NULL, 0, format, arglist );
    va_end( arglist );
    len = len + 1 + 7;
    msgbuf = malloc( len );
    strcpy( msgbuf, "Error: " );
    va_start( arglist, format );
    vsnprintf( &msgbuf[7], len, format, arglist );
    va_end( arglist );
    return( msgbuf );
  }

void main()
  {
    char *msg;

    msg = fmtmsg( "%s %d %s", "Failed", 100, "times" );
    printf( "%s\n", msg );
    free( msg );
  }