c - printf displays something weird

Question

There is such code:

#include <stdio.h>

int main() {
  float d = 1.0;
  int i = 2;
  printf("%d %d", d, i);
  getchar();
  return 0;
}

And the output is:

0 1072693248

I know that there is error in printf and first %d should be replaced with %f. But why variable i is printed wrong (1072693248 instead of 2)?

Answer 1

Since you specified %d instead of %f, what you're really seeing is the binary representation of d as an integer.

Also, since the datatypes don't match, the code actually has undefined behavior.

EDIT:

Now to explain why you don't see the 2:

float gets promoted to double on the stack. Type double is (in this case) 8 bytes long. However, since your printf specifies two integers (both 4 bytes in this case), you are seeing the binary representations of 1.0 as a type double. The 2 isn't printed because it is beyond the 8 bytes that your printf expects.