calling a function with a char and a variable number of arguments - ios

Question

so what i am trying to do is whenever i touch a button, it calls a function with both a char and some variable number of arguments (in this case two ints that are both worth 24).
- (IBAction)buttonPressed:(id)sender {
number = 24;
printf_to_debug("some text %d %d ",number, number);
//printf(" %d %d ",number, number);
}
however, when i call the function it seems to always change my ints to some big number, which i don't understand.
void printf_to_debug (char* fmt, ...) {
va_list args;
va_start( args, fmt );
printf(fmt, args);
charString = [NSString stringWithUTF8String: fmt];
charString = [NSString stringWithFormat:charString, args];
debugTextString = [NSString stringWithFormat:#"%#\r%#",charString, debugTextString];
va_end( args );
}
does anyone see a problem with my code?

Answer 1

You have to use vprintf() to print the arguments given by a va_list:
va_list args;
va_start (args, fmt );
vprintf(fmt, args);
va_end( args );
The corresponding NSString method is initWithFormat:arguments::
NSString *s = [[NSString alloc] initWithFormat:#(fmt) arguments:args];

Answer 2

Let's take a look at what your code actually does.
The first important line is: printf_to_debug("some text %d %d ",number, number);
Which looks fine, it doesn't really matter what number is it'll be treated as an int anyways.
Next you initialize the variable arguments list which is fine but then you try and print using:
printf(fmt, args);
Now, When you use that code, you seem to want printf to treat each individual object in your variable arguments list as a separate parameter, however, printf doesn't care. All it sees is that you passed it a parameter. It doesn't know or care what the parameter was, all it knows and cares about is that you told it to treat the first parameter it was given as a decimal number (that's what the "%d" says). So now, it takes va_list and treats it as a number and prints it. Since you only provided one argument, the second number you get is complete garbage, and I suspect XCode tried to warn you about that (command line clang does).
Now for the simple solution:
When your trying to print a variable arguments list as seperate objects use the vprintf function. So in your case it would be vprintf(fmt, args);