What's wrong with this code?

Question

int main(void) {
    char *p = "hello";
    char *q = "world";
    *p = *q;
    printf("%s", *p);
}

I am trying to overwrite hello with world...

Answer 1

Those string literals are stored in readonly memory, in the data section of your executable. You cannot (and should not try) to overwrite that memory.

Answer 2

This line:

*p = *q;

Will set the char (singular) pointed to by p to the char pointed to by q.

You want strncpy if you want to copy strings. (Although see Ed's comment about the read-only nature of the strings in your code).

Answer 3

You're just overwriting the first character of hello, i.e. h with the first character of world, i.e. w.

Also, if you want to stick with your original code,

p = q;
printf("%s", p);

Also, with p = q you are not overwriting anything. p now points to the first character of world.

As Ed said, you cannot overwrite the data stored in p with the data in q.

Answer 4

char *p = "hello"; char *q = "world"; the both variables are constant, unchangeable

Answer 5

Firstly, your code only tries to overwrite the first character of "Hello" with first character of "World", i.e. it attempts to turn "Hello" into "Wello".

Secondly, you are trying to modify a string literal. Sitring litrerals are not modifiable. You can't "overwrite" string literal. Your attempt to overwrite "Hello" with "World" is not much different from an attempt to overwrite 5 with 8 by doing 5 = 8.

For further reading see http://stackoverflow.com/questions/1614723/why-is-this-c-code-causing-a-segmentation-fault/1614739#1614739

Thirdly, in order to print a string with printf you have to pass a pointer to the first character, not the first character itself. Your printf should look as printf("%s", p)