C - The %x format specifier

Break-down:

• 8 says that you want to show 8 digits
• 0 that you want to prefix with 0's instead of just blank spaces
• x that you want to print in lower-case hexadecimal.

Quick example (thanks to Grijesh Chauhan):

#include <stdio.h>int main() {    int data = 29;    printf("%x\n", data);    // just print data    printf("%0x\n", data);   // just print data ('0' on its own has no effect)    printf("%8x\n", data);   // print in 8 width and pad with blank spaces    printf("%08x\n", data);  // print in 8 width and pad with 0's    return 0;}

Output:

1d1d      1d0000001d

Also see http://www.cplusplus.com/reference/cstdio/printf/ for reference.

%08x means that every number should be printed at least 8 characters wide with filling all missing digits with zeros, e.g. for '1' output will be 00000001

The format string attack on printf you mentioned isn't specific to the "%x" formatting - in any case where printf has more formatting parameters than passed variables, it will read values from the stack that do not belong to it. You will get the same issue with %d for example.%x is useful when you want to see those values as hex.

As explained in previous answers, %08x will produce a 8 digits hex number, padded by preceding zeros.

Using the formatting in your code example in printf, with no additional parameters:

printf ("%08x %08x %08x %08x");

Will fetch 4 parameters from the stack and display them as 8-digits padded hex numbers.