Correctly #including SDL in multi-filed project [duplicate] - c++

Question

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Why does the order of '-l' option in gcc matter? [duplicate]
(3 answers)
Closed 5 years ago.
I have just started to use C++ and SDL, and I have begun to create a basic Breakout clone to get my head around the semantics. To modularise what I have so far, I have created two header files core.h and paddle.h.
I am having difficulty with correctly including SDL with these modules. Initially, the project compiled when all I had was the main file breakout.cpp, paddle.h and paddle.cpp. At this stage, the 'Core' class was located in breakout.cpp, and as soon as I migrated it into its own file, the compiler started to get upset.
As it stands, it's a very simple set up that can be illustrated as follows:
breakout ---> core ---> paddle
Which leads me to believe that I am making a rookie oversight. Or that I'm linking the files incorrectly in Makefile.
Here is the code:
breakout.cpp
#include "SDL2/SDL.h"
#include "SDL2/SDL_image.h"
#include <stdio.h>
#include <string>
#include "core.h"
int main(int argc, char* args[]) {
Core gCore;
gCore.runGame();
return 0;
}
core.h
#pragma once
#include "paddle.h"
class Core {
public:
Core();
~Core();
void runGame();
private:
static const int SCREEN_WIDTH = 640, SCREEN_HEIGHT = 480;
SDL_Window* gWindow;
SDL_Renderer* gRenderer;
Paddle* p1;
void render();
};
paddle.h
#pragma once
#include <string>
class Paddle {
friend class Core;
public:
Paddle( SDL_Renderer* gRenderer );
~Paddle();
void free();
private:
static const int VELOCITY = 5;
int xPos, yPos, pWidth, pHeight;
SDL_Texture* pSprite;
SDL_Rect* pRect;
bool loadFromFile( SDL_Renderer* gRenderer, std::string path );
int getXPos(); int getYPos();
int getWidth(); int getHeight();
};
core.cpp
#include "SDL2/SDL.h"
#include "SDL2/SDL_image.h"
#include <stdio.h>
#include "paddle.h"
#include "core.h"
Core::Core() {
// Set up SDL
if ( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
printf( "SDL could not initialise! SDL Error: %s\n", SDL_GetError() );
}
else {
if ( !SDL_SetHint( SDL_HINT_RENDER_SCALE_QUALITY, "1" ) ) {
printf( "Warning: Linear texture filtering not enabled!" );
}
else {
gWindow = SDL_CreateWindow( "SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT,
SDL_WINDOW_SHOWN );
if ( gWindow == NULL ) {
printf( "Could not create window. SDL Error: %s\n", SDL_GetError() );
}
else {
gRenderer = SDL_CreateRenderer( gWindow, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC );
if ( gRenderer == NULL ) {
printf( "Renderer could not be created! SDL Error: %s\n", SDL_GetError() );
}
else {
// Initialise renderer colour
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
// Initialise PNG loading
int imgFlags = IMG_INIT_PNG;
if ( !( IMG_Init( imgFlags ) & imgFlags ) ) {
printf( "SDL_image could not be initialised! SDL_image Error: %s\n", IMG_GetError() );
}
}
}
}
}
}
Core::~Core() {
SDL_DestroyRenderer( gRenderer ); gRenderer = NULL;
SDL_DestroyWindow( gWindow ); gWindow = NULL;
// Quit SDL subsystems
IMG_Quit();
SDL_Quit();
}
void Core::runGame() {
// Main loop flag
bool quit = false;
// Event handler
SDL_Event e;
// p1 = new Paddle( gRenderer );
while ( !quit ) {
while( SDL_PollEvent( &e ) != 0 ) {
//User requests quit
if( e.type == SDL_QUIT ) {
quit = true;
}
}
// Clear screen
SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF );
SDL_RenderClear( gRenderer );
// Render game assets
render();
// Update screen
SDL_RenderPresent( gRenderer );
}
}
void Core::render() {
// Set rendering space and render to screen
SDL_Rect pRenderQuad = { p1->xPos, p1->yPos, p1->pWidth, p1->pHeight };
// Render to screen
SDL_RenderCopy( gRenderer, p1->pSprite, NULL, &pRenderQuad );
}
paddle.cpp
#include "SDL2/SDL.h"
#include "SDL2/SDL_image.h"
#include <stdio.h>
#include <string>
#include "paddle.h"
Paddle::Paddle(SDL_Renderer* gRenderer) {
xPos = 300; yPos = 400;
pWidth = 0; pHeight = 0;
loadFromFile( gRenderer, "paddle.png" );
}
Paddle::~Paddle() {
free();
}
bool Paddle::loadFromFile(SDL_Renderer* gRenderer, std::string path) {
// Get rid of preexisting texture
free();
SDL_Texture* nTexture = NULL;
SDL_Surface* lSurface = IMG_Load( path.c_str() );
if ( lSurface == NULL ) { printf( "Unable to load image %s! SDL_image Error: %s\n", path.c_str(), IMG_GetError() ); }
else {
nTexture = SDL_CreateTextureFromSurface( gRenderer, lSurface );
if ( nTexture == NULL ) { printf( "Unable to load texture from %s! SDL Error: %s\n", path.c_str(), SDL_GetError() ); }
else {
pWidth = lSurface->w;
pHeight = lSurface->h;
}
SDL_FreeSurface( lSurface ); // Surface no longer needed
}
pSprite = nTexture;
return pSprite != NULL;
}
void Paddle::free() {
if ( pSprite != NULL ) {
SDL_DestroyTexture( pSprite );
pWidth = 0; pHeight = 0;
}
}
// Getter methods
int Paddle::getXPos() { return xPos; } int Paddle::getYPos() { return yPos; }
int Paddle::getWidth() { return pWidth; } int Paddle::getHeight() { return pHeight; }
And I have also included the Makefile, as there could easily be something wrong there too.
Makefile
OBJS = breakout.cpp
DEPS = paddle.h core.h
CC = g++
COMPILER_FLAGS = -w
LINKER_FLAGS = -lSDL2 -lSDL2_image
OBJ_NAME = breakout
%.o: %.cpp $(DEPS)
$(CC) -c -o $# $< $(COMPILER_FLAGS)
all : $(OBJS)
$(CC) $(OBJS) $(COMPILER_FLAGS) $(LINKER_FLAGS) paddle.cpp core.cpp -o $(OBJ_NAME)
Error log
g++ breakout.cpp -w -lSDL2 -lSDL2_image paddle.cpp core.cpp -o breakout
/tmp/cc0H2fKM.o: In function `Paddle::loadFromFile(SDL_Renderer*, std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
paddle.cpp:(.text+0x111): undefined reference to `IMG_Load'
paddle.cpp:(.text+0x121): undefined reference to `SDL_GetError'
paddle.cpp:(.text+0x15a): undefined reference to `SDL_CreateTextureFromSurface'
paddle.cpp:(.text+0x16a): undefined reference to `SDL_GetError'
paddle.cpp:(.text+0x1b8): undefined reference to `SDL_FreeSurface'
/tmp/cc0H2fKM.o: In function `Paddle::free()':
paddle.cpp:(.text+0x203): undefined reference to `SDL_DestroyTexture'
/tmp/ccDHGaLY.o: In function `Core::Core()':
core.cpp:(.text+0x12): undefined reference to `SDL_Init'
core.cpp:(.text+0x1e): undefined reference to `SDL_GetError'
core.cpp:(.text+0x44): undefined reference to `SDL_SetHint'
core.cpp:(.text+0x86): undefined reference to `SDL_CreateWindow'
core.cpp:(.text+0xa1): undefined reference to `SDL_GetError'
core.cpp:(.text+0xd1): undefined reference to `SDL_CreateRenderer'
core.cpp:(.text+0xee): undefined reference to `SDL_GetError'
core.cpp:(.text+0x127): undefined reference to `SDL_SetRenderDrawColor'
core.cpp:(.text+0x138): undefined reference to `IMG_Init'
core.cpp:(.text+0x149): undefined reference to `SDL_GetError'
/tmp/ccDHGaLY.o: In function `Core::~Core()':
core.cpp:(.text+0x17a): undefined reference to `SDL_DestroyRenderer'
core.cpp:(.text+0x195): undefined reference to `SDL_DestroyWindow'
core.cpp:(.text+0x1a5): undefined reference to `IMG_Quit'
core.cpp:(.text+0x1aa): undefined reference to `SDL_Quit'
/tmp/ccDHGaLY.o: In function `Core::runGame()':
core.cpp:(.text+0x1ea): undefined reference to `SDL_PollEvent'
core.cpp:(.text+0x218): undefined reference to `SDL_SetRenderDrawColor'
core.cpp:(.text+0x228): undefined reference to `SDL_RenderClear'
core.cpp:(.text+0x244): undefined reference to `SDL_RenderPresent'
/tmp/ccDHGaLY.o: In function `Core::render()':
core.cpp:(.text+0x2d1): undefined reference to `SDL_RenderCopy'
collect2: ld returned 1 exit status
make: *** [all] Error 1
I'd would really appreciate your support on not just the problem at hand. But also if any general suggestions about my code can be made.
Thanks

Answer 1

The order of the flags on your compiler switch matter.
Libraries to be passed to the linker should be last.
And using a -w makes no sense as it's usually -W (capital) followed by some kind of directive, such as -Werror -Wall etc.
Suggesto: remove -w flag and move the -l switches to the end.