void *

This is a discussion on void * within the C++ Programming forums, part of the General Programming Boards category; Hi. I've recently seen the use of "void *" in functions and i'm trying to figure out how it all ...

  1. #1
    alloc(MEM_NEWBIE)
    Guest

    void *

    Hi. I've recently seen the use of "void *" in functions and i'm trying to figure out how it all works. If a function accepts 'void *' as a parameter that means i can pass in a pointer to anything i want, right? Like:

    void Func(void * ThisPtr)
    {
    //do something with ThisPtr
    }

    int Num = 1;
    char Array[10];
    struct AStruct
    {
    int a, b, c;
    }

    Func(&Num);
    Func(&Array);
    Func(&AStruct);

    My compiler accepts that but i want to understand how it works. How can i determine the scope of what the ThisPtr points to? Like if i wanted to use fwrite of something in the Func(void *) function, how could i get the size of what i passed in (besides passing it in as another parameter...)?

    Could memory be allocated in function Func() like this?

    ThisPtr = new char[6];

    Or something? How could something like that be done?

    Sorry for all the questions but once i get it in my head that i want to know something, i want to know all about it.

  2. #2
    Evil Member
    Join Date
    Jan 2002
    Posts
    638
    Using void pointers in that manner is a good way to get a core dump. The type of a pointer dictates the length of the variable it denotes, so a void* is just an address, nothing more. There are a few good uses for void*'s, but that is getting into some advanced concepts, like pseudo pointers and funky casting.

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