Passing string along function. Pointer.

I'm making a 13h, DJGPP-compiled game. I just
wrote a function that writes letters to the
screen (and it took me a long time. Not a good
programmer :))The function accepts two parameters;
a position-variable, and a text-string...

Code:

---

#define A 0
#define B 1
#define C 2

class cXYCOORD{
  public:
    int x;
    int y;
};

void WriteText(cXYCOORD Position, char *string){
  int StringLength = strlen(string);
  int Pixels = Position.x;
 
  for(int i=0;i<StringLength;i++){
    int choice = string[i];
    switch(choice){
      case 65: Alphabet[A]->image->DrawImage(Position); break;
      case 66: Alphabet[B]->image->DrawImage(Position); break;
    ...
    /*More Lines of Code. Moves to another line,
      etc. They aren't important, though*/
    }
  }
}

---

Here's my question. Back at the old, blue cprog
board, I asked how to pass a text-string along
a function. Someone said I should declare a
char pointer as a parameter. I did. char *string.

What exactly is this variable holding when I
pass a string through it, though? Pointers hold
variable-addresses, right? What am I assigning to
this pointer? It isn't an address... Is this a
bad way of passing a string? Will my program/game
screw up later?

WriteText(RightHere, "Write This");

Thanks a lot,
ethic.

> Pointers hold
variable-addresses, right? What am I assigning to
this pointer? It isn't an address...

That's exactly what you are doing. You are passing an address to the first character in the string. The compiler knows where the string ends because, in C++, strings are always terminated with a NULL (zero) character.

Usually, pointers are the best way to pass data around, because you are only passing an (32 bit) address to some data. If you were to pass the data itself, this could be mean large amounts of memory are copied on each call (which is slower).

> Will my program/game
screw up later?

Not if you take care of deleting any heap memory you use. The code you have given seems OK.

Let me give some example:


[\code]

char s[] = "Hello World";
cXYCOORD p;
p.x = 5;
p.y = 5;
WriteText(p, s);

[code]

This is fine because s is declare on the stack; the compiler knows how big it is and will ensure its deleted when it goes out of scope.

However, the following (on its own) is not fine:

[\code]

char* s = new char[20];
strcpy(s, "Hello World");
cXYCOORD p;
p.x = 5;
p.y = 5;
WriteText(p, s);

[code]


Because you have declare s as a pointer and created the memory for it on the heap, which is not deleted.

In this case, you need to call:

delete[] s;

after the call to WriteText.

Pointer in C/C++ may seem complicated, but it's really worth learning if you want write reliable & fast code. It's a bit to much to describe in detail here, however. I suggest you find a good book, it does really all make sense.

Damm! I still can't remember my code tags.

edit your post and fix them!

> edit your post and fix them!

Can't. Not registered. Don't wanna a be.