Pointer

This is a discussion on Pointer within the C Programming forums, part of the General Programming Boards category; I have a variable called myVar so i declared and initialised it. Code: int myVar; Now, I would like to ...

  1. #1
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    Pointer

    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*.

  2. #2
    DESTINY BEN10's Avatar
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    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.
    HOPE YOU UNDERSTAND.......

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  3. #3
    C++まいる!Cをこわせ! Elysia's Avatar
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    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.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    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?

  5. #5
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    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.

  6. #6
    C++まいる!Cをこわせ! Elysia's Avatar
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    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.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  7. #7
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    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

  8. #8
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    Well, I want to ask one more question.

    void (*foo)(int);
    can it be written as
    void *foo(int);
    ?

  9. #9
    C++まいる!Cをこわせ! Elysia's Avatar
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    First is a function pointer, second is a function prototype taking an int, returning void*.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  10. #10
    DESTINY BEN10's Avatar
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    Quote Originally Posted by valthyx View Post
    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 *.
    HOPE YOU UNDERSTAND.......

    By associating with wise people you will become wise yourself
    It's fine to celebrate success but it is more important to heed the lessons of failure
    We've got to put a lot of money into changing behavior


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  11. #11
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    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.

  12. #12
    C++ Witch laserlight's Avatar
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    Quote 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);
    }
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  13. #13
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    IC, ok, now I understand. Thanks

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