char *c="1234". Address stored in c is always the same

Question

This was a question asked by an interviewer:

#include<stdio.h>

int main()
{
    char *c="123456";
    printf("%d\n",c);
    return 0;
}

This piece of code always prints a fixed number (e.g. 13451392), no matter how many times you execute it. Why?

Answer 1

Your code contains undefined behavior: printing a pointer needs to be done using %p format specifier, and only after converting it to void*:

printf("%p\n", (void*)c);

This would produce a system-dependent number, which may or may not be the same on different platforms.

The reason that it is fixed on your platform is probably that the operating system always loads your executable into the same spot of virtual memory (which may be mapped to different areas of physical memory, but your program would never know). String literal, which is part of the executable, would end up in the same spot as well, so the printout would be the same all the time.

Answer 2

To answer your question, the character string "123456" is a static constant in memory, and when the .exe is loaded, it always goes into the same memory location.

What c is (or rather what it contains) is the memory address of that character string which, as I said, is always at the same location. If you print the address as a decimal number, you see the address, in decimal.

Of course, as @dasblinkenlight said, you should print it as a pointer, because different machines/languages have different conventions about the size of pointers versus the size of ints.