Pointer

**valthyx** · 08-10-2009

I have a variable called myVar

so i declared and initialised it.

Code:

int myVar;

Now, I would like to create a pointer pointing to myVar
What should i do?

1. int* myPtr = &myVar;
OR
2. void* myPtr = &myVar;

What is the difference between void* and int*? does it depend on what it is pointing to?
For example, if the pointer is pointing to an int, it has to be declared using int*.

**BEN10** · 08-10-2009

I think it's better to declare like this.

Code:

int* myPtr = &myVar;

void * is a generic pointer, which can point to any type of variable, be it char,int or float. int * means it can only point to an int. I preffered 1 because you know that myVar is an int.

**Elysia** · 08-10-2009

Don't use void* if you can avoid it. Because it's generic, the compiler loses all type information about what it points to. This can easily cause bugs on your part and make the compiler unable to do optimizations.

**valthyx** · 08-10-2009

By the way, can anyone explain the use of a pointer to a function.

eg. int* call ( int* number)

why must the function be a pointer type?

**sean** · 08-10-2009

That's not a pointer TO a function, that's a function that returns a pointer TO an int. So it would be any function that fits this form:

Code:

int* call(int* number) {
    int* result;
    ...
    return result;
}

However, unless you're returning a pointer to dynamically allocated memory, you're returning a pointer to data that has now gone out of scope - so be careful.

**Elysia** · 08-10-2009

Remember also that functions are always stored somewhere in the memory (code segment, most likely), so therefore they have an address, and thus you can create a pointer to point to that function. That's called a function pointer.

**roaan** · 08-10-2009

Have a look at this tutorial. It really is a good one (that is how i understood this)

Function Pointers in C and C++ - Cprogramming.com

**valthyx** · 08-10-2009

Well, I want to ask one more question.

void (*foo)(int);

can it be written as

void *foo(int);

?

**Elysia** · 08-11-2009

First is a function pointer, second is a function prototype taking an int, returning void*.

**BEN10** · 08-11-2009

Originally Posted by valthyx

Well, I want to ask one more question.

can it be written as ?

Code:

void (*foo)(int);

Here foo is a pointer to a function that takes an int and returns nothing(void).

Code:

void *foo(int);

Here foo is a function that takes an int and returns void *.

**valthyx** · 08-11-2009

Code:

void (*foo)(int);

Here foo is a pointer to a function that takes an int and returns nothing(void).
Code:

void *foo(int);

Here foo is a function that takes an int and returns void *.

Well, what does it really mean? I don't really get the second one.

**laserlight** · 08-11-2009

Originally Posted by valthyx

Well, what does it really mean? I don't really get the second one.

The explanation for the second one seems pretty clear to me. For example, here is a possible definition of such a function:

Code:

void *foo(int n)
{
    return malloc(n);
}

**valthyx** · 08-11-2009

IC, ok, now I understand. Thanks

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