For further education, a pointer is simply an address in memory. Memory (RAM) is a giant array of bytes (numbers with 8 binary bits that can range from 0 to 255). Everything in a program--from PlayerTypes numbers to CvWString text strings to int IDs to CvCity objects--is stored in this giant array. Each slot in the array has a numeric address which starts at 0 for the first byte and increments by 1 for the next slot.
A simple value like an int requires 4 bytes in the SDK and thus it requires 4 slots in the giant memory array. You can store a pointer to it using the & (address) operator:
Code:
int x;
int* pointerToX = &x;
Pointers are useful for allowing a function to modify the value of a variable passed to it. Normally in C and C++ everything is
passed by value which means the value of the variable is copied into a temporary variable for the function to use. If the function changes it, the original variable doesn't change.
Code:
void addTwo(int value) {
value += 2;
}
int x = 5;
addTwo(x);
print(x);
The above code prints 5 because addTwo() only gets a copy of x's value, in this case 5. Adding 2 to its local copy of 5 doesn't change the original value of x. But you can use a pointer to allow addTwo() to change the original value:
Code:
void reallyAddTwo(int* value) {
(*value) += 2;
}
int x = 5;
reallyAddTwo(&x);
print(x);
Here addTwo() expects a pointer to an int, and the caller takes the address of x to pass a pointer to it to addTwo(). (*value) just means "follow this pointer" and allows you to set the value. It's similar to the -> you see a lot in the SDK, for example "pCity->getID()".
Pointers to CvCity and CvPlayer objects are no different. If you were to write a function that took a CvCity, calling it would make a complete copy of the CvCity before calling the function. First, this would be expensive in runtime cost, but more importantly it wouldn't allow the function to modify the original CvCity.
One thing to keep in mind is that pointers are just numbers. On 32-bit systems they are 4 bytes just like an int. When you pass a pointer to a function such as reallyAddTwo() above, you are actually passing a copy of the pointer. But since a pointer and its copy both point to the same memory address (they have the same value) it doesn't matter.
