c++ - SDL UpdateWindowSurface() returns -1 if called from a class (in separate file) -

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today started c++/sdl2 snake clone, , i've been looking ways make code neater, -particularly classes. tried put sdl code used window/display in class. when run code, the window closes instantly. error tests set in display.cpp, tells me through console sdl_updatewindowsurface() (in display.update()) returning -1. why happen when rearrange code this?

with code load image in main() , display through class' function applysurface(). idea have classes/objects game's grid/board, snake, etc., -each calling applysurface() own images. feel free tell me if bad idea altogether.

main.cpp:

#include <sdl.h> #include "display.h"  sdl_event event; sdl_surface* image = nullptr;  int main(int argc, char* args[]) {     display display;     display.loadimage("image.bmp");      if (sdl_init(sdl_init_everything) == -1)         return false;      bool quit = false;      while (!quit)     {         while (sdl_pollevent(&event))         {             if (event.type == sdl_quit)                 quit = true;         }          display.applysurface(0, 0, image, display.windowsurface);         display.update();     }      sdl_freesurface(image);     sdl_quit();     return 0; }

display.h:

#pragma once #include <sdl.h> #include <string> #include <iostream>  class display { public:     sdl_window* window;     sdl_surface* windowsurface;      display();     sdl_surface *loadimage(std::string filename);     void applysurface(int x, int y, sdl_surface *source, sdl_surface *destination, sdl_rect *clip = nullptr);     void update();     ~display(); private:     const int window_width = 612;     const int window_height = 632;     const int screen_bpp = 2; };

display.cpp:

#pragma once #include "display.h"  display::display() {     window = sdl_createwindow("snake", sdl_windowpos_centered, sdl_windowpos_centered, window_width, window_height, sdl_window_shown);      if (window == null)         std::cout << "error: sdl_createwindow failed." << std::endl;      windowsurface = sdl_getwindowsurface(window); }  sdl_surface* display::loadimage(std::string filename) {     sdl_surface* loadedimage = null;     sdl_surface* optimizedimage = null;      loadedimage = sdl_loadbmp(filename.c_str());      if (loadedimage != null)     {         optimizedimage = sdl_convertsurface(loadedimage, windowsurface->format, 0);          sdl_freesurface(loadedimage);          if (optimizedimage != null)             sdl_setcolorkey(optimizedimage, sdl_true, sdl_maprgb(optimizedimage->format, 255, 255, 255));     }      return optimizedimage; }   void display::applysurface(int x, int y, sdl_surface *source, sdl_surface *destination, sdl_rect *clip) {     sdl_rect offset;      offset.x = x;     offset.y = y;      sdl_blitsurface(source, clip, destination, &offset); }  void display::update() {     if (sdl_updatewindowsurface(window) == -1)         std::cout << "error: sdl_updatewindowsurface() failed." << std::endl; }  display::~display() {     sdl_freesurface(windowsurface);     windowsurface = null;      sdl_destroywindow(window);     window = null; }

this valid use of classes structure code. sdl_init needs come before other sdl functions, means you're best off moving sdl_init top of main or adding display constructor. if add beginning of display constructor means can have 1 display class object running @ time, fine in case.


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