c - Can I use scanf to capture a directive with a width specified by a variable?

Question

I have the following code:

scanf(" %Xs %Ys", buf1, buf2);

Where X and Y should be integers. The problem is that the values for X and Y are compile-time constants, and even if I wanted to hard-code the values into the format string, I can't, because I don't know the values. In printf, you can send a width variable along with the arguments with "%*s". Is there anything analogous for scanf?

EDIT: To clarify, constants are known at compile time, but not at coding time, and not by me at all. They may vary by platform or implementation, and they may change after I'm done. Even did they not, I still wouldn't want to have buffer sizes duplicated in format strings, ready to segfault the minute I forget to keep them synchronized.

Answer 1

You may produce the format string with sprintf():

sprintf( format, " %%%is %%%is", X, Y );
scanf(format, buf1, buf2);

EDIT: amazing, but the following gcc code is working:

#include <stdio.h> 

#define LIST(...) __VA_ARGS__ 

#define scanf_param( fmt, param, str, args ) {   
  char fmt2[100];  
  sprintf( fmt2, fmt, LIST param );  
  sscanf( str, fmt2, LIST args  );  
} 

enum { X=3 };
#define Y X+1 

int main(){
  char str1[10], str2[10];

  scanf_param( " %%%is %%%is", (X,Y), " 123 4567", (&str1, &str2) );

  printf("str1: '%s'   str2: '%s'
", str1, str2 );
}