SDL_BlitSurface is throwing segmentation fault error

Question

I am trying to display a menu using the Menu class. But in the function draw() of that class, the SDL_BlitSurface is not working and is throwing a segmentation default while executing this line :

SDL_BlitSurface(el.surfaceNormal, NULL, surface, &el.rect); 

Here is the code of the function:

void Menu::draw(SDL_Surface* surface) {
    for(int i=0; i<menuElementList.size(); i++){
        auto el = menuElementList.at(i);
        SDL_BlitSurface(el.surfaceNormal, NULL, surface, &el.rect); 
    }
}

The struct I am using in vector:

struct menuElement{
    SDL_Surface* surfaceNormal;
    SDL_Surface* surfaceHover;
    SDL_Rect rect;
    std::string text;
};

Normally, I should be able to render all of the surface present in the vector, but for a reason I can't figure, it is not working.

The code to populate the vector:

void Menu::addMenu(std::string name, int x, int y) {
    menuElement m;
    TTF_Font* Sans = TTF_OpenFont("OpenSans-Light.ttf", 25); 
    if(!Sans){
        std::cout << TTF_GetError() << std::endl;
    }
    SDL_Color White = {255, 255, 255};  
    SDL_Surface* surfaceMessage = TTF_RenderText_Solid(Sans, name.c_str(), White); 
    m.surfaceNormal = surfaceMessage;    
    SDL_Color Red = {255, 0, 0}; 
    SDL_Surface* hoverMessage = TTF_RenderText_Solid(Sans, name.c_str(), Red);
    m.surfaceHover = hoverMessage;
    SDL_Rect rect;
    rect.x = rect.y = 50;
    m.rect = rect;
    m.text = name;
    SDL_FreeSurface(surfaceMessage);
    SDL_FreeSurface(hoverMessage);
    menuElementList.push_back(m);
}

I know that the vector gets populated because I can display the text attribute of each element in it. What's wrong?

Answer 1

Well the error is pretty simple you would have realized if had debugged a bit, here is a MVCE that you SHOULD have done.

#include <SDL2/SDL.h>
#include <SDL2/SDL_ttf.h>
#include <iostream>
#include <vector>
#include <string>

#define HEIGHT 600
#define WIDTH  800

using namespace std;

struct menuElement{
    SDL_Surface* surfaceNormal;
    SDL_Surface* surfaceHover;
    SDL_Rect rect;
    std::string text;
};

std::vector<menuElement> menuElementList;

void add_element(std::string name, int x, int y) {
    menuElement m;
    TTF_Font* Sans = TTF_OpenFont("OpenSans-Light.ttf", 25);
    if(!Sans){
        std::cout << TTF_GetError() << std::endl;
    }
    SDL_Color White = {255, 255, 255};
    SDL_Surface* surfaceMessage = TTF_RenderText_Solid(Sans, name.c_str(), White);
    m.surfaceNormal = surfaceMessage;
    SDL_Color Red = {255, 0, 0};
    SDL_Surface* hoverMessage = TTF_RenderText_Solid(Sans, name.c_str(), Red);
    m.surfaceHover = hoverMessage;
    SDL_Rect rect{x, y, 50, 50};  // You were never using x and y before now it draws at that position with a rect of size 50x50
    m.rect = rect;
    m.text = name;
  //  SDL_FreeSurface(surfaceMessage); << how is this not crashing in your system when blitting, I don't know
  //  SDL_FreeSurface(hoverMessage);
    menuElementList.push_back(m);
}

int main() {
    SDL_Init(SDL_INIT_VIDEO);

    TTF_Init();
    SDL_Window *window = SDL_CreateWindow("TextFail", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, WIDTH, HEIGHT, SDL_WINDOW_SHOWN);

    SDL_Surface *surface = SDL_GetWindowSurface(window);
    bool quit = false;
    SDL_Event event;

    add_element("ello", 20, 20);
    add_element("Bye", 40, 40);


    while (!quit) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }

        for (auto &el : menuElementList)
            SDL_BlitSurface(el.surfaceNormal, NULL, surface, &el.rect);

        SDL_UpdateWindowSurface(window);
    }

    SDL_DestroyWindow(window);
    SDL_Quit();

    return 0;
}

I commented the 2 lines that are messing with you, even if the vector gets populated its getting populated with uninitialized data since you FREE the surfaces, you should do that when freeing the menuElement (If you're using C++ in the menuElement destructor for example or on a free_menu_element(menuElement *e) { .. } function if C)

Remember when you copy pointers you copy the direction of memory they point to and not its contents.

You were also never using x and y!