Question

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What is the difference between char a[] = “string”; and char *p = “string”;

Could you please explain what is the difference between these? ^^

            //difference between:
            char* sz1 = "blah";
            char  sz2[] = "blah";

            //and also please explain these
            char *sz3 = new char[512];
            char *sz4[512] = { 0, };
            char sz5[512];

Answer 1

"blah" is a const char [5]. In the first line, that array is decayed into a pointer to be stored in your variable as a pointer to the first element. It is also a pointer to non-const characters that points to const characters. It should be:

const char *sz1 = "blah";

In the second (thanks jrok), it creates an actual array and initializes it with {'b', 'l', 'a', 'h', '\0'}.

char *sz3 = new char[512];

This allocates 512 * sizeof (char) bytes of memory for the chars and sz3 will point to the beginning. This is stored on the heap, as opposed to the stack, so don’t forget to delete[] it.

char *sz4[512] = { 0, };

This creates an array of 512 pointers to characters and initializes them all to 0 (NULL). The comma isn’t needed, it’s just easier to add onto the initializer list afterwards. The spiral rule can be used here to determine sz4 is an array of 512 (one right) pointers (one left) to char (two left).

char sz5[512];

This creates an array (on the stack) of 512 characters.

All but the second-last can effectively be replaced with std::string.