Question

Possible Duplicate:
getting segmentation fault in a small c program

Here’s my code:

char *const p1 = "john";

p1[2] = 'z';  //crashes

printf("%s\n", p1);

I know p1 is a “read-only” variable, but I thought I could still modify the string (“john” ). I appreciate any tips or advice.

Answer 1

You cannot safely modify string literals, even if the pointer doesn’t look const. They will often be allocated in read-only memory, hence your crashes – and when they’re not in read-only memory modifying them can have unexpected consequences.

If you copy to an array this should work:

char tmp[] = "john";
char *const p1 = tmp;
p1[2] = 'z'; // ok