Re: [Dev-C++] void to...

[Per W. <pw...@ia...>]

See below

/Per W


On Wed, 9 Jul 2003, Neszt Tibor wrote:

> Hello!
>
> I have a problem. First of all, see the source code:
>
>
> This one is works:
> /* -------------------------------------------------------------------- */
> int putbuffer(                            /* returns 0 on success       */
>     void *AppState,
>     unsigned char *buffer,                /* buffer to put              */
>     long length                           /* length of buffer           */
> ) {
>   size_t ret;
>
>   crc = CrcUpdate(crc, buffer, length);
>
>   ret = fwrite(buffer, 1, (size_t) length, (FILE *) AppState);
>
>   if ((size_t) length != ret)
>     return 1;
>   else
>     return 0;
> }
>
>
>
>
> I tried to change it to work in memory instead of writing to file:
>
> /* -------------------------------------------------------------------- */
> int putbuffer_mem(                        /* returns 0 on success       */
>     void *AppState,
>     unsigned char *buffer,                /* buffer to put              */
>     long length                           /* length of buffer           */
> ) {
>   int i;

    unsigned char *tmpptr = (unsigned char*)AppState;

>
>   crc = CrcUpdate(crc, buffer, length);
>
>   for (i=0;i<length;i++) {
// Here you declare a NEW variable AppState completely different
// from the parameter you sent in. Of course AppState++ doesn't
// do anything since the compiler is clearly aware that you don't
// use this new variable outside of the loop.
// Besides - you can't increment a void* pointer since it doesn't
// point to a data type of a known size.
>     char *AppState=buffer[i];   // #1
>     AppState++;                 // #2

      tmpptr[i] = buffer[i];
      // or *tmpptr++ = *buffer++;

>     printf("a\n");
>   }
>   return 0;
> }
>
> This second one does nothing as I check the AppState.
> Can I use (void *) to allocate memory?
> The original call was
>
> putbuffer( (void *) out, .....)  ( out = fopen("name", "wb"); )
>
>
> And now, I call
>
> putbuffer_mem( mem, ....) ( mem = (char *) malloc(size); )
>
>
> What would be the problem?
>
> Is there any mode to mix the #1 and the #2 lines?
>
>
> Thanks Your help in advance.
>
> Regards,
>   Neszt Tibor
>
>
>
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