c++ _vsnprintf unexpected format string -

i have logging function takes in variable number of arguments , uses _vsnprintf format them. problem when debug ocr automation string returns sent log, if file said this:

this bitmap says %n

then sent logging function this:

void log(lpcstr msg, ...) {     char log[max_allowed];         int length = sizeof(log) / sizeof(log[0]);      va_list argptr;     va_start( argptr, pzmsg );      // our msg accidentally has %     if ( strchr(msg, '%') ) {           // debug assertion - no parameters passed         _vsnprintf( log, length, msg, argptr );     }      log[length-1] = (char)0;     va_end( arg_ptr ); } 

is there way, along check '%' can check if there no arguments? thank you.

the traditional way make sure can't expanded printf is

log("%s", yourstring); 

of course, add variant of log takes 1 argument, or count number of variable arguments , not format string if there aren't any.