varargs function crashing - c++

Question

I have a function that is supposed to take a variable number of arguments (using varargs) based on a format string:
void va(const char* name, const char* argformat, ...) {
int numOfArgs = strlen(argformat);
std::string buf = "asdf";
va_list listPointer;
va_start(listPointer, numOfArgs);
char* blah;
for(int i = 0; i < numOfArgs; i++) {
switch (argformat[i]) {
case 's':
cout << va_arg(listPointer, char*) << endl;
break;
case 'i':
cout << va_arg(listPointer, int) << endl;
break;
case 'f':
cout << va_arg(listPointer, float) << endl;
break;
case 'b':
cout << va_arg(listPointer, bool) << endl;
break;
default:
break;
}
}
va_end(listPointer);
return;
}
int main() {
va("fe", "sb", "asdf", true);
return 0;
}
It crashes.
If I change
cout << va_arg(listPointer, char*) << endl;
to
cout << va_arg(listPointer, char) << end;
it prints "a".
What am I doing wrong?

Answer 1

It should be va_start(listPointer, argformat). va_start takes the last named parameter as its second argument. (Which technically means that you don't need to pre-calculate the length of the argument string at all — just iterate over the characters (iterating over the varargs as you go) until you get to the end of the string.)