About pointer to function (Soved by myself)

**hchingwong** · 08-04-2010

----I love the pointer in C very well. I have just learned how to declare a pointer to a function and how to use it:

Code:

    void (*start)(void);    /*The star should be placed with the word*/
    start = &hello;
    (*start)();

----But I'm not willing to use the pointer with a lot of different types. I'm wondering is it possible to transform a pointer between a void pointer and a pointer to function. This is strange, I can't figure out how to write it.

----And this is my solution:

Code:

    (*                      /*Get the value of the function pointer */
        (void (*)(void))
/*A function pointer type*/
        start               /*which is transformed from the void pointer to the type above.*/
    )
    ();                     /*Excute*/

----Oh my dear, it works, how amazing is that, and by the way I got the answer myself. Thanks God and also thank you everybody for sharing it with me.

**Elysia** · 08-04-2010

What is the point of thanking something that doesn't exist?

**laserlight** · 08-04-2010

Originally Posted by hchingwong

I'm wondering is it possible to transform a pointer between a void pointer and a pointer to function.

"A pointer to void may be converted to or from a pointer to any incomplete or object type." As such, I would say no, at least not in general.

Originally Posted by hchingwong

And this is my solution: (...) Oh my dear, it works

I think that you are misleading yourself. It looks like you are casting start to be a pointer to a function that takes no argument and returns void... but that is the type of start to begin with.

**hchingwong** · 08-06-2010

Yah, I'm actually want to declare a void pointer and cast it to a function pointer.
This one

Code:

    void *start

instead of this one

Code:

    void (*start)(void);

It works. But I know now this is some kind of bad thing. Maybe I should save the pointer with long long and then cast it to whatever type. This is just a joke. I now uncomfortable with it. Thank you laserlight and thank you Elysia for reading my post.

**hchingwong** · 08-06-2010

and ';'. Another mistake.

**Elysia** · 08-06-2010

You cannot create a void datatype. You must create the appropriate type, eg function pointer, then store it in void*. You can later cast it back into its original type. This is usually how generic programming is done in C.
Don't save pointers in non-void pointers. Different pointers can vary in size. Therefore, it is only guaranteed that you can cast something to void* and back. Not between S* and T* and back.

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