C++ Notes: Pointers and Subscripts

Character strings

The string "Hello" is a char array, and therefore a pointer to the first char of that array, and therefore can be assigned to a char pointer. Char operations often use pointers.

char* message;      // message is a pointer to a char
message = "Hello";  // assigns the address of the first char

strcpy written with subscripts in simple style

This is at straight-forward solution with subscripts (altho better with do-while). We'll make this a void function, altho the library function returns the address of the first parameter.

void strcpy(char a[], const char b[]) {
    int i = 0;
    while (b[i] != 0) {
        a[i] = b[i];
        i++;
    }
    a[i] = 0;  // put terminating 0 at end.
}

strcpy written with pointers in simple style

void strcpy(char* a, char* b) {
    while (*b != 0) {
        *a = *b;
        a++;
        b++;
    }
    *a = 0;  // put terminating 0 at end.
}

strcpy written with subscripts, optimized slightly

Shorten by embedding assignment in if, and using fact that zero value is false.

void strcpy(char a[], const char b[]) {
    int i = 0;
    while (a[i] = b[i]) { // assignment, not comparison!
        i++;
    }
}

strcpy written with pointers in a cryptic style.

To make this really compact (but not more efficient) use postincrement operators. C++ programmers often seem to like this insanely cryptic code, but it isn't good style.

void strcpy(char* a, char* b) {while (*a++ = *b++);}