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 (could use do-while). We'll make this a void function, altho the library function returns the address of the first parameter.

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

strcpy written with pointers.

To make this really compact (tho without any greater efficiency, we can use postincrement operators to the pointers within the if.

void strcpy(char* a, char* b) {
   while (*a++ = *b++) { // assignment, not comparison!
       ;
   }
 }