String literals: pointer vs. char array

You can look at string literal as "a sequence of characters surrounded by double quotes". This string should be treated as read-only and trying to modify this memory leads to undefined behavior. It's not necessarily stored in read only memory, and the type is char[] and not const char[], but it is still undefined behavior. The reason the type is not const is backwards compability. C didn't have the const qualifier in the beginning. In C++, string literals have the type const char[].

So how come that you get segmentation fault?

• The main point is that char *ptr = "string literal" makes ptr to point to the read-only memory where your string literal is stored. So when you try to access this memory: ptr[0] = 'X' (which is by the way equivalent to *(ptr + 0) = 'X'), it is a memory access violation.

On the other hand: char b[] = "string2"; allocates memory and copies string "string2" into it, thus modifying it is valid. This memory is freed when b goes out of scope.

Have a look at Literal string initializer for a character array