I have written the following code which accepts variable arguments:

void dprintf(FILE *fp,char *fmt,...)
{
        char OldMsg[BUFSIZ];
        va_list lArgs;

        if(fmt && *fmt)
        {
            fmt[strlen(fmt)-1]='\0'; /* Remove ending \n */
            va_start(lArgs, fmt);
            vsprintf(OldMsg, fmt, lArgs);
            va_end(lArgs);
            fprintf(fp, "%s at %s_%02d\n", 
                        OldMsg, Run.date, Run.hour);
        }
}

I am calling the function as follows:

dprintf(flog,"\t%s(%s): Unable to insert node\n", 
             program_name, sccs_ver);