From: Gruber Gerhard <gruber2 AT ibm DOT net>
Newsgroups: comp.os.msdos.djgpp,comp.lang.c
Subject: Re: Functions in struct's... possible?  How?
Date: Mon, 25 Aug 1997 11:25:29 +0200
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Jeff Weeks wrote:
> 
> I'd like to have a function in a struct that I've created.  I realise I
> can't just stick a functions in there, so I used a pointer to a
> function.  Here's what my struct looks like:
> 
> typedef struct {
>   VesaInfo card;           // information about the video card
>   VesaModeInfo mode;       // information about the current mode
>   int bytes_per_line;      // the number of bytes per scanline
>   int size;                // the size in bytes of the whole screen
>   char *address;           // the address of actual video memory
>   void (*blit)(char *);    // a routine to copy a virtual screen to
> memory
> } Driver;
> 
> And then I define an instance and set blit to something:
> 
> Driver driver;
> driver.blit = lfb_blit;
> 
> But when I try to call the actual function, it crashes.  I know the
> lfb_blit() function is not at fault (I've tested it separately), so the
> problem is in calling the function from the struct.  I do it as follows:
> 
> char *virt = (char *)malloc(640*480*2);
> driver.blit(virt);
> 
> Can C not do this?  Is there no way to call a function from a struct?
> If there is a way (perferable a portable way!) could you please tell me.
> 
> If it's not possible, then I'll just write an assembly language
> proceedure to load in the address of blit and jump to it, but I'd perfer
> to be able to do it simply with C code.

This should work ok. I use it myself in a parser where I defined for
each keyword a function that processes the parameters. Are you sure that
your function lfb_blit() works correct? Also you might check the models
(depending on your system). Which memory model do you use?

-- 

Bye,
   Gerhard