G++: Undefined reference to class::method - linux

Question

I am trying to create an interface for my program using SDL2. The problem is that when I include my .h file, the compiler can't find the .cpp even tough I linked everything. None of the methods I found on the internet work and when compiling in visual studio, the code works perfectly fine. What is more strange is that when I try to make my classes inherit from others, I get the same error from the parent class. I am also using the latest version of Ubuntu. Furthermore, I installed all the libraries required for SDL2.
This is the error:
/usr/bin/ld: /tmp/ccWHZ70h.o: in function `interface::init(char const*)':
interface.cpp:(.text+0xd6): undefined reference to `interface::renderer'
/usr/bin/ld: interface.cpp:(.text+0xdd): undefined reference to `interface::renderer'
/usr/bin/ld: interface.cpp:(.text+0x106): undefined reference to `interface::renderer'
/usr/bin/ld: /tmp/ccWHZ70h.o: in function `interface::LoadTexture(char const*)':
interface.cpp:(.text+0x1bd): undefined reference to `interface::renderer'
/usr/bin/ld: /tmp/ccWHZ70h.o: in function `interface::DrawTexture(SDL_Texture*, SDL_Rect, SDL_Rect)':
interface.cpp:(.text+0x20d): undefined reference to `interface::renderer'
collect2: error: ld returned 1 exit status
make: *** [MakeFile:2: all] Error 1
I compile using make -f on this file:
all:
g++ mainClient.cpp client.cpp interface.cpp -lSDL2main -lSDL2 -lSDL2_image -lSDL2_mixer -lSDL2_ttf -o client.exe
clean:
rm -f *~client-exe
The code works perfectly fine without the interface class.
This is the inteface.h code:
#pragma once
#include <SDL2/SDL.h>
#include <SDL2/SDL_image.h>
#include <SDL2/SDL_mixer.h>
#include <SDL2/SDL_ttf.h>
#include <SDL2/SDL_render.h>
#include <iostream>
class interface
{
private:
int width, height;
SDL_Window* window;
bool state;
static SDL_Renderer* renderer;
public:
interface(int w,int h);
~interface(){};
int init(const char* titlu);
void loop();
void render();
SDL_Texture* LoadTexture(const char* filename);
void DrawTexture(SDL_Texture* tex, SDL_Rect imgRect, SDL_Rect destRect);
};
And this is the interface.cpp code:
#include "interface.h"
interface::interface(int w, int h)
{
width = w;
height = h;
state = true;
}
int interface::init(const char* title)
{
if(SDL_Init(SDL_INIT_EVERYTHING) == 0)
{
window = SDL_CreateWindow(title,SDL_WINDOWPOS_CENTERED,SDL_WINDOWPOS_CENTERED,width,height,0);
if(window == NULL)
{
std::cout<<"Eroare la crearea ferestrei!\n";
state = false;
}
renderer = SDL_CreateRenderer(window,-1,0);
if(renderer == NULL)
{
std::cout<<"Eroare la crearea rendererului!\n";
state = false;
}
else
{
SDL_SetRenderDrawColor(renderer,255,255,255,255);
}
}
else
{
std::cout<<"ERROR AT INIT EVERYTHING\n";
state = false;
}
}
SDL_Texture* interface::LoadTexture(const char* filename)
{
SDL_Surface* tempSurface = IMG_Load(filename);
if(!tempSurface)
{
std::cout<<"Eroare la imaginea: "<<filename<<SDL_GetError<<std::endl;
}
SDL_Texture* tex = SDL_CreateTextureFromSurface(renderer,tempSurface);
SDL_FreeSurface(tempSurface);
return tex;
}
void interface::DrawTexture(SDL_Texture* tex, SDL_Rect imgRect,SDL_Rect destRec)
{
SDL_RenderCopyEx(renderer,tex,&imgRect,&destRec,0,NULL,SDL_FLIP_NONE);
}
This is the code of mainClient.cpp where I include interface.h:
#include "client.h"
#include "interface.h"
int main()
{
client *Client = new client;
interface *screen = new interface(800,600);
screen->init("ReadsProfiler");
Client->init();
Client->loop();
}
I get the same error if I don't use client.h, so I'm not gonna add the code to that as well.

Answer 1

Because rendereris static, you also need to declare it in the .cpp file.
Add it to interface.cpp, for example under #include "interface.h":
SDL_Renderer* interface::renderer;