Size of short int is 2 bytes (16 bits) on my 64 bit processor and mingw compiler but when I convert short int variable to a binary string using itoa function, it returns string of 32 bits:
#include<stdio.h>
int main(){
char buffer [50];
short int a=-2;
itoa(a,buffer,2); //converting a to binary
printf("%s %d",buffer,sizeof(a));
}
Output
11111111111111111111111111111110 2
The answer is in understanding C's promotion of short datatypes (and char's, too!) to int's when those values are used as parameters passed to a function and understanding the consequences of sign extension.
This may be more understandable with a very simple example:
#include <stdio.h>
int main() {
printf( "%08X %08X\n", (unsigned)(-2), (unsigned short)(-2));
// Both are cast to 'unsigned' to avoid UB
return 0;
}
/* Prints:
FFFFFFFE 0000FFFE
*/
Both parameters to printf() were, as usual, promoted to 32 bit int's. The left hand value is -2 (decimal) in 32bit notation. By using the cast to specify the other parameter should not be subjected to sign extension, the printed value shows that it was treated as a 32 bit representation of the original 16 bit short.
itoa() is not available in my compiler for testing, but this should give the expected results
itoa( (unsigned short)a, buffer, 2 );