Question

I have the following code that crashes at the line where I am initializing ch:

    char * p = "Test";
    char ch = *p++;
    printf("Here : %s\n%c", p, ch);

However the following code has no problem:

    char * p = "Test";
    char ch = *p++;
    ch++;
    printf("Here : %s\n%c", p, ch);

Answer 1

In the first situation, you’re trying to change the T in the “Test” string compiled into the program, which is held in a part of memory that your code isn’t meant to change (usually; there are some environments where it’s allowed, but usually it isn’t). That’s because (*p)++ means (loosely speaking) *p = *p + 1 (e.g., get the character pointed to by p, increment it, and write it back), and of course, *p is pointing to the compiled-in “Test”.

Your second version doesn’t have that problem, because you’re incrementing ch, which you are allowed to change. Your second version actually increments two different things, in fact; first it does char ch = *p++; which retrieves the character at *p and then increments p (now it points to the “e” in “Test”), and then you do ch = ch++. (You probably meant just ch++; there, since ++ operates directly on its operand.)