Segmentation fault, array hell? - c++

Question

there seemed to be a lot of people with the segmentation fault problem but I couldn't seem to find any that related to my program, if there is a thread I'm sorry, I looked through multiple though and couldn't find it.
pretty much everything so far:
#include <SDL.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string>
#include <time.h>
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int maxLandMass = SCREEN_WIDTH * SCREEN_HEIGHT;
const int landPercentage = 30;
const int maxHeight = 200;
const int numAnts = 10;
int main(int argc, char **argv)
{
int currentLandMass = 0;
int ants[numAnts][3]={{0}}; //x,y,pDir (0123,NESW)
std::string rules[numAnts]={0};
std::string rule;
int states = 2;
std::cout << "Which rule would you like to use? ";
std::cin >> rule;
if(rule == "")
{
rule = "RL";
}
else if(rule == "RND" || rule == "rnd")
{
std::cout << "How many states? ";
std::cin >> states;
}
srand(time(NULL));
for(int i = 0;i < numAnts;i++)
{
ants[i][0] = rand() % SCREEN_WIDTH;
ants[i][1] = rand() % SCREEN_HEIGHT;
ants[i][2] = rand() % 4;
if(rule != "RND" && rule != "rnd")
{
rules[i] = rule;
}
else
{
std::string tempRule;
for(int s = 0; s < states; s++)
{
int r = rand() % 2;
if(r == 0){ tempRule += "L"; }
if(r == 1){ tempRule += "R"; }
}
rules[i] = tempRule;
}
std::cout << rules[i] << "\n";
}
SDL_Window* window = NULL;
SDL_Surface* surface = NULL;
if(SDL_Init(SDL_INIT_VIDEO) < 0)
{
printf("SDL could not initialize! SDL_Error: %s\n", SDL_GetError());
}
else
{
window = SDL_CreateWindow("SDL Tutorial", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if( window == NULL )
{
printf("Window could not be created! SDL_Error: %s\n", SDL_GetError());
}
else
{
surface = SDL_GetWindowSurface(window);
SDL_FillRect(surface, NULL, SDL_MapRGB(surface->format, 0x00, 0x00, 0x00));
SDL_UpdateWindowSurface(window);
}
}
//Uint16 *pixels = (Uint16 *) surface->pixels;
/////////////////////////////
int grid[SCREEN_HEIGHT][SCREEN_WIDTH]={{0}};
int heights[SCREEN_HEIGHT][SCREEN_WIDTH]={{0}};
int prevState = 0;
for(int a = 0; a < numAnts; a++)
{
//TODO add stuff here
}
SDL_DestroyWindow(window);
SDL_Quit();
return 0;
}
When it runs it should start with a console window to get some input from the user then switch to an SDL window and do its thing, but the console window tells me:
terminate called after throwing an instance of 'std::logic_error'
what():basic_string::_S_construct null not valid
I have a feeling its something to do with how I have initialised (or at least tried to) the arrays.
The part that I added last was the bit below the ////// line I made.
let me know if you will need more info, Ill get it as soon as I can, and I apologise for my programs current state, its messiness is driving me a bit mad too but (until I broke it) it worked :P

Answer 1

You are initializing your array of strings with zeros. That's an invalid initialization.
Interestingly, had you picked any other number, you'd get a clearer error message, telling you that you're doing an invalid conversion from int to const char* (which is a c-style string, and the closest valid input type std::string has a constructor for).
Unfortunately, the zero initialization is confusing your compiler to think you're actually assigning a pointer, which it may convert, but luckily it checks and sees that the pointer is NULL, and therefore bails out with the error message you saw: basic_string::_S_construct null not valid.
I took your code and removed all the SDL part, it compiled and reproduced the error.
I then replaced
std::string rules[numAnts]={0};
with
std::string rules[numAnts];
which uses the default constructor to create empty strings for all elements, and now it seems to work.