SDL_image's IMG_Load do not work - sdl-image

Question

I am using IMG_Load() to load png file, but it simply not working.
loadedImage = IMG_Load(filename.c_str()); after this sentence, loadedImage is still NULL,not error happened.
PS:I am using VS C++2008, png file is in the develop folder. Here is my code:(It is exactly what Lazy Foo like)
//The headers
#include "SDL.h"
#include "SDL_image.h"
#include <string>
#pragma comment( linker, "/subsystem:\"windows\" /entry:\"mainCRTStartup\"" )
//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;
//The surfaces
SDL_Surface *image = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *load_image( std::string filename )
{
//The image that's loaded
SDL_Surface* loadedImage = NULL;
//The optimized image that will be used
SDL_Surface* optimizedImage = NULL;
//Load the image using SDL_image
loadedImage = IMG_Load(filename.c_str());
//If the image loaded
if( loadedImage != NULL )
{
//Create an optimized image
//cout<<"Flag";
optimizedImage = SDL_DisplayFormat( loadedImage );
//Free the old image
SDL_FreeSurface( loadedImage );
}
//Return the optimized image
return optimizedImage;
}
void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination )
{
//Rectangle to hold the offsets
SDL_Rect offset;
//Get offsets
offset.x = x;
offset.y = y;
//Blit the surface
SDL_BlitSurface( source, NULL, destination, &offset );
}
bool init()
{
//Initialize all SDL subsystems
if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
{
return false;
}
//Set up the screen
screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
//If there was an error in setting up the screen
if( screen == NULL )
{
return false;
}
//Set the window caption
SDL_WM_SetCaption( "PNG test", NULL );
//If everything initialized fine
return true;
}
void clean_up()
{
//Free the surface
SDL_FreeSurface( image );
//Quit SDL
SDL_Quit();
}
int main( int argc, char* args[] )
{
//Initialize
if( init() == false )
{
return 1;
}
//Load the image
image = load_image( "look.png" );
//If there was a problem in loading the image
if( image == NULL )
{
return 5;
}
//Apply the surface to the screen
apply_surface( 0, 0, image, screen );
//Update the screen
if( SDL_Flip( screen ) == -1 )
{
return 1;
}
//Wait 2 seconds
SDL_Delay( 2000 );
//Free the surface and quit SDL
clean_up();
return 0;
}
The output return 5.

Answer 1

my bad.
I just copy SDL_image.dll to exe floder.
I should also copy zlib1.dll and libpng12-0.dll
Actually, all the dll is need, because if there is not such dll, the program won't give any error prompt, which is confusing.

Answer 2

If you download libpng from the website, you will find a file called libpng12.dll. Copying that file into system32 does not work, because SDL_image actually looks for a file called "libpng12-0.dll". I found that out after having implemented the IMG_GetError() method in my code. The error message says it very clearly...
So what you do is copying libpng12.dll to system32 and rename it to libpng12-0.dll! And everything works just fine.