Buffers in standard functions

In a standard function like:

Code:

size_t fwrite(const void *buf, size_t size, size_t count, FILE *stream);

How does the function cycle through *buf? Does it use the '+' operator? '++'? Is it implemention-defined? I'm trying to write a linked list class that overloads the necessary operators to work in such a function. So I need to know how such a function works internally.

> How does the function cycle through *buf?
Casts it back into unsigned char*
The interface is void* so you can safely point at whatever without getting lots of warnings.

Well you could if you were using it in C, but I notice this is posted on the C++ board.

> I'm trying to write a linked list class that overloads the necessary operators to work in such a function.
Overload the << and >> operators then?
cout << myLinkedListNode;

As prelude has just pointed out in another recent post, you can't simply fwrite() a block of memory if your type isn't a POD. You need a proper method of serialising your data.

>So I need to know how such a function works internally.
It works the wrong way for what you're trying to do. Consider a naive implementation:

Code:

#include <cstdio>

using namespace std;

size_t jsw_fwrite ( const void *buf, size_t size, size_t count, FILE *stream )
{
  if ( size == 0 )
    return 0;

  const unsigned char *p = static_cast<const unsigned char *> ( buf );
  size_t n = 0;

  for ( ; n < count; n++ ) {
    for ( size_t i = 0; i < size; i++ )
      fputc ( *p++, stream );

    if ( ferror ( stream ) )
      break;
  }

  return n;
}

No amount of operator overloading will make that work for a non-POD type.

Balls.