Why Use Pointers in C?

Question

I\'m still wondering why in C you can\'t simply set something to be another thing using plain variables. A variable itself is a pointer to data, is it not? So why make poi

Answer 1

No, a variable is not a pointer to data. If you declare two integers with int x, y;, then there is no way to make x and y refer to the same thing; they are separate.

Whenever you read or write from a variable, your computer has to somehow determine the exact location of that variable in your computer's memory. Your computer will look at the code you wrote and use that to determine where the variable is. A pointer can represent the situation where the location is not known at the time when you compile your code; the exact address is only computed later when you actually run your code.

If you weren't allowed to use pointers or arrays, every line of code you write would have to access specific variables that are known at compile time. You couldn't write a general piece of code that reads and writes from different places in memory that are specified by the caller.

Note: You can also use arrays with a variable index to access variables whose location is not known at compile time, but arrays are mostly just syntactical sugar for pointers. You can think about all array operations in terms of pointer operations instead. Arrays are not as flexible as pointers.

Another caveat: As AnT points out, the location of local variables is usually on the stack, so they are a type of variable where the location isn't known at compile time. But the only reason that the stack works for storing local variables in a reentrant function is that your compiler implements hidden pointers called the stack pointer and/or frame pointer, and functions use these pointers to find out which part of memory holds their arguments and local variables. Pointers are so useful that the compiler actually uses them behind your back without telling you.