Thread: More pointer problems :(

No matter what I seem to try whenever I compile my prog I get ther following error:

Code:

warning: passing argument 1 of ‘blit_and_fade’ from incompatible pointer type

Heres my best guess, main:

Code:

#include "screen.h"
#include "vector.h"

SDL_Surface *screen = NULL;
SDL_Event event; 

int main()
{
	screen = SDL_SetVideoMode(GRAPHICS_W, GRAPHICS_H, 32, SDL_SWSURFACE);	
	Uint32 buffer[SCREEN_BUFFER_SIZE]={0xFFFFFFFF};
	while(1)
	{
		blit_and_fade(&buffer, &screen, SCREEN_BUFFER_SIZE, 0.95);
		SDL_Flip(screen);
		while(SDL_PollEvent(&event))if(event.type==SDL_KEYDOWN) break;
	}
	return 0;
}

and function:

Code:

void blit_and_fade(Uint32 **src, SDL_Surface **dst, Uint32 size, float mod)
{
	Uint32 *pix = (Uint32*)(*dst)->pixels;
	Uint32 *buf = (*src);	
	Uint32 r_b, g;
	int fade = (int) (mod * 256.0);

	for(int i=0; i<size; i++, pix++, buf++)
	{
		*pix = *buf;	
		r_b = (((*buf & 0x00FF00FF) * fade) & 0xFF00FF00) >> 8;		
		g   = (((*buf & 0x0000FF00) * fade) & 0x00FF0000) >> 8;				
		*buf = r_b | g;
	}
}

How cn I get my pointer types compatible?

Use Uint32 (*src)[] instead, perhaps (since &buffer is a pointer to an array, which is not a pointer to a pointer).

I tried that but gcc still gives me the same warning. Thanks for the suggestion tho.

I changed the Uint32 to unsigned long and for some reason the warnings went away and the prog works w/o segfaulting any more.

Originally Posted by mike_g

I changed the Uint32 to unsigned long and for some reason the warnings went away and the prog works w/o segfaulting any more.

Your solution is correct and will work because you are passing an address to blit_and_fade(), and the type used for addresses in most systems is unsigned long.

But a more precise solution would be to explicitly tell the compiler that you are indeed passing a pointer-to-pointer of a Uint32.

Code:

	while(1)
	{
		blit_and_fade((Uint32 **)&buffer, &screen, SCREEN_BUFFER_SIZE, 0.95);
		...

matsp: Yeah I always compile with -Wall. That was the only warning I was getting. My current code is doing what tabstop suggested:

Code:

#include "screen.h"
#include "vector.h"

SDL_Surface *screen = NULL;
SDL_Event event; 

int main()
{
	screen = SDL_SetVideoMode(GRAPHICS_W, GRAPHICS_H, 32, SDL_SWSURFACE);	
	long buffer[SCREEN_BUFFER_SIZE];	
	for(int i=0; i<SCREEN_BUFFER_SIZE; i++) buffer[i]=0xFFFFFFFF;

	int quit = 0;	
	while(! quit)
	{
		blit_and_fade(&buffer, &screen, SCREEN_BUFFER_SIZE, 0.9);
		SDL_Flip(screen);
		while(SDL_PollEvent(&event)) if(event.type==SDL_KEYDOWN) quit = 1;
		SDL_Delay(20);
	}
        return 0;
}

and:

Code:

void blit_and_fade(long (*src)[], SDL_Surface **dst, Uint32 size, float mod)
{
	Uint32 *pix = (Uint32*)(*dst)->pixels;
	Uint32 *buf = (Uint32*)(*src);	
	Uint32 r_b, g;
	int fade = (int) (mod * 256.0);

	for(int i=0; i<size; i++, pix++, buf++)
	{
		*pix = *buf;	
		r_b = ((( *buf & 0x00FF00FF) * fade) & 0xFF00FF00) >> 8;		
		g   = ((( *buf & 0x0000FF00) * fade) & 0x00FF0000) >> 8;				
		*buf = r_b | g;
	}
}

Which was working w/o errors or warnings.

In vector.h I had these defined:

Code:

#ifndef Uint8
	#define Uint8 unsigned char
#endif 
#ifndef Uint16
	#define Uint16 unsigned short
#endif 
#ifndef Uint32
	#define Uint32 unsigned long
#endif

but the Uints are also defined in SDL. Could this be causing a problem?

Ok I replaced the #defines with typedefs, changed the code so that its passing on buffer, reverted the long to Uint32 in the function. It works now with no warnings and the code is a little bit tidier. Thanks matsp.