From: "YUBS" <jdebever1 AT home DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: help: void pointers
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Date: Sat, 07 Aug 1999 07:04:36 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hi, I'm having some trouble using void pointers. I'm writing a function that
will allocate enough memory for any of my types by using a void pointer as a
parameter in the function. I.e.

void pcx_init (void *image, char type)

So say I have the following type:


typdef struct pcx_image_typ
{
    char *buffer;
    int width, height;
} pcx_image, *pcx_image_ptr

I want to be able to pass a pointer to a variable of type pcx_image to
pcx_init and have it allocate width*height memory for buffer. The problem
I'm getting is that DJGPP keeps complaining that I'm "dereferencing "void *"
pointer" and that "request for memeber "buffer" in something not a structure
or a union".

here's my exact code:

void pcx_init(void *image, char type)
{
    switch (type)
        {
            case 's': {
                            if (!(((pcx_image_ptr)(image->buffer)) = (char
* )malloc (image->width* image->height)))
                         }
        }
}

I left out the other case since I figured I should isolate the problem and
typing it out here would only confuse things. Now, I had to manually copy
this so I may have made a typo, but I just wanted to give you the idea of
what I'm trying to do. Basically, buffer is going to store a pcx file. I
read in the size of the pcx file, store it in width and height, and then
call pcx_init to allocate the memory for the buffer. Thing is, I have other
types that I'd like to use the same function to allocate memory for, and
using void pointers seemed (at the time:-) to be a good idea. Obviously
there are numerous ways around this, but I'd like to figure out how to use
void pointers anyway, so I may aswell use this scenario as a learning tool.
Thanks for any help you can give and if you need me to clarify my
explaination (its a little difficult to explain) don't hesitate to ask.
Thanks again.

-Josh de Bever