Annoying SDL Problem

[dellwood]

Hi,

One of my SDL functions in "Engine.cpp" is spitting out an error that I can't seem to pinpoint. Here's the code.

Engine.h


#ifndef ENGINE_H
#define ENGINE_H

#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include "SDL/SDL_ttf.h"
#include <iostream>
#include <string>
#include <vector>
#include <map>

using namespace std;

class Init {
private:
int win_width, win_height, win_bpp; //used for setting up the window
string win_caption; //the text that goes in the window caption
int win_time; //the time the window stays open ( for dev purposes only )
string file, handle; //the filename and image handle strings
SDL_Surface *nativeImage; // used for loading image
SDL_Surface *optimizedImage; // used for optimizing the image
string filename; // filename for loadImage
int xCoord, yCoord; // placeSurface offsets
SDL_Surface *source;
SDL_Surface *destination; //for surface blitting

public:
SDL_Surface *screen; // needs to be used outside of function
Init();
~Init();
void Load( int win_width, int win_height, int win_bpp, string win_caption, int win_time );
SDL_Surface *loadImage( string filename );
void placeSurface( int xCoord, int yCoord, SDL_Surface *source, SDL_Surface* destination );
void Quit();
};



#endif // ENGINE_H


Engine.cpp

#include "Engine.h"


/* Constructor */
Init::Init() {
int win_width = 640;
int win_height = 480;
int win_bpp = 32;
string win_caption = "Default Caption";
int win_time = 3;
SDL_Surface *screen = NULL;
string filename = " ";
string handle = " ";
SDL_Surface *nativeImage = NULL;
SDL_Surface *optimizedImage = NULL;
int xCoord = 0;
int yCoord = 0;
SDL_Surface *source = NULL;
SDL_Surface *destination = NULL;
}

/* Destructor */
Init::~Init() {
}

/* Class Functions */

void Init::Load( int win_width, int win_height, int win_bpp, string win_caption, int win_time ) {

/* Initialize Subsystems */
if( SDL_Init( SDL_INIT_EVERYTHING < 0 ) ) {
cerr << "Failed to Initialize subsystems: ", SDL_GetError();
}

/* Set up screen */
screen = SDL_SetVideoMode( win_width, win_height, win_bpp, SDL_SWSURFACE );

/* Make sure screen initialized */
if( screen == NULL ) {
cerr << "Failed to load screen: ", SDL_GetError();
}

/* Set Caption */
SDL_WM_SetCaption( win_caption.c_str(), NULL );


/* Convert win_time from seconds to milliseconds */
win_time *= 1000;

/* Wait win_time seconds */
SDL_Delay( win_time );

}

SDL_Surface *loadImage( string filename ) {

/* Load the image */

SDL_Surface *nativeImage = IMG_Load( filename.c_str() );

if( nativeImage != NULL ) {
/* Optimize the image */
SDL_Surface *optimizedImage = SDL_DisplayFormat( nativeImage );
}
else {
cerr << "Error loading image: " << SDL_GetError() << endl;
}

return optimizedImage;
}

void placeSuface( int xCoord, int yCoord, SDL_Surface *source, SDL_Surface *destination ) {

/* Create a rectangle */
SDL_Rect surface;

/* Set the */
surface.x = xCoord;
surface.y = yCoord;

/* Blit the surface to the screen */
SDL_BlitSurface( source, NULL, destination, &surface);
}

void Init::Quit() {
/* Quit the program (more to be added here later */
SDL_Quit();
}


#include <iostream>
#include "Engine.h"

int main( int argc, char** args ) {

SDL_Surface * image;

/* Create class objects */
Init main_init;

/* Load the object functions */
main_init.Load( 640, 480, 32, "A Test Program", 3 );

image = main_init.loadImage( "image.png" );

main_init.placeSurface( 0, 0, image, main_init.screen );

main_init.Quit();

return 0;
}

And last but not least, the error:


g++ -o Main main.cpp Engine.cpp -lSDL -lSDL_image ~/Programs/C++/syi-engine
Engine.cpp: In function ‘SDL_Surface* loadImage(std::string)’:
Engine.cpp:68: error: ‘optimizedImage’ was not declared in this scope

It seems to think I haven't declared "optimized image," even though I did in the header as well as in the constructor...right ? :D I have been mulling this over for 30 + minutes without success:-k.

Thanks :).

-Josh

[wmcbrine]

Hint: Note the word "scope".

[JordyD]

Hint: Note the word "scope".

And not of this (http://en.wikipedia.org/wiki/Telescopic_sight) variety, but rather this (http://en.wikipedia.org/wiki/Scope_(programming)) one.

[dellwood]

After looking here ( http://cplusplus.syntaxerrors.info/index.php?title=%E2%80%98bar%E2%80%99_was_not_decl ared_in_this_scope ) as well as your wiki link I did add Init:: between SDL_Surface and *loadImage, but that still gave the same error ( after forcing me to fix a few others ). Was that the 'scope' problem you were talking about, or is it something else?

Thanks.

-Josh

[JordyD]

After looking here ( http://cplusplus.syntaxerrors.info/index.php?title=%E2%80%98bar%E2%80%99_was_not_decl ared_in_this_scope ) as well as your wiki link I did add Init:: between SDL_Surface and *loadImage, but that still gave the same error ( after forcing me to fix a few others ). Was that the 'scope' problem you were talking about, or is it something else?

Thanks.

-Josh

That's not the scope I was talking about.

If you declare a variable inside of a certain scope, when it exits that scope, your variable is gone.

(Some) things that increase scope:
functions,
loops,
if statements,
classes

Now take a look at the variable that the compiler says is non-existent:

SDL_Surface *loadImage( string filename ) {

/* Load the image */

SDL_Surface *nativeImage = IMG_Load( filename.c_str() );

if( nativeImage != NULL ) {
/* Optimize the image */
SDL_Surface *optimizedImage = SDL_DisplayFormat( nativeImage );
}
else {
cerr << "Error loading image: " << SDL_GetError() << endl;
}

return optimizedImage;
}

So, the loadImage function is in its scope. Think of a filesystem, like this: /loadImage
We load an image into nativeImage. Scope is still /loadImage
We go into an if statement, scope is now /loadImage/if
We declare optimizedImage and define it.
We exit the if statement, and now scope is /loadImage again.
We try to return optimizedImage, but it does not exist, since it was declared out of scope (/loadImage/if specifically). If we declared it in /loadImage, then we could still use it, and it would be initialized to SDL_DisplayFormat(nativeImage).

[monraaf]

This makes me sad :( It seems that people don't even take the time anymore to learn the language basics.

[dellwood]

I am still learning the basics. I told myself that when I got to point x in my programming book , I would look back and try to devise an exercise that incorporates everything I had learned up to that point, which included functions, classes, and simple API's ( I know SDL may not have been the best choice, but I used a very small portion of it ). Since I spent a most of today writing/debugging/re-writing this code, and I had it down to one error, I said what the heck, I'll stick it up on the forums and see if I can actually get this to work.

So hopefully your not sad anymore :).

-Josh

[monraaf]

Ah okay, so this is part of your learning process. Personally I think it's better to stick to plain old 'boring' console programs learning the basics of the language first before diving into external libraries.

[wmcbrine]

I know SDL may not have been the best choiceYour problem has nothing to do with SDL.

[dwhitney67]

There are also problems with the implementation of the methods loadImage() and placeSuface() [sic] in the Engine.cpp file. Once again, the problems are related to "scope".