Thread: How is it I can change a string literal even if its declared const?

I had an embarrassing moment on SO where a user asked if it was safe to pass a String literal to a function. I answered that passing either a `char*` or `char[]` would create a `char*` on the stack once the function was called. Because of my misunderstanding I said that changing the address of the char* is legal even if its declared `const`. But what I didn't know was changing the char array pointed it pointed to was also legal.

So I tried myself and lo and behold it works even if the parameter in the function `func()` is `const`! But its illegal to change an element within the array? It just seems inconsistent to me.

Here is the code I wrote:

Code:

#include <stdio.h>


void func(const char *x, int* y) {
    printf("func output:\n");
    printf("%p\n", x); 
    printf("%s\n", x); 
    x = "New string"; //how is this legal?
    x = x + 1000; //chage address pointed to by the char*
    printf("%s\n\n", x);

    printf("%p\n", y);
    printf("%d\n", *y);

    y = y + 10;
    printf("%p\n", y);
    printf("%d\n", *y);
}

int main(void) {
    const char* ptr = "String";
    int x = 25;
    int * int_ptr = &x;
    func(ptr, int_ptr);
    puts("In main() \n");
    printf("%s\n", ptr);
    ptr = "New string";
    printf("%s\n", ptr); //able to change the string literal. Why?
    return 0;
}