Why can't I return a vector<vector<int>> (Process returned -1073741819 (0xC0000005))

I tried to make a grid-based program in C++. But each time I run it, I get the same error (Show in title). I know it is quite a common error but after reading carefully through the code, I wasn't able to spot any mistake:

#include <iostream>
#include <vector>

using namespace std;

using grid = vector<vector<int>>;

int getNeighboursCount(grid g,int x,int y)
{
    int nCount = 0;
    if(x > 0 && y > 0){if(g[x-1][y-1] == 1){++nCount;};};
    if(x > 0){if(g[x-1][y] == 1){++nCount;};};
    if(y > 0){if(g[x][y-1] == 1){++nCount;};};
    if(x < g.size() && y < g[x].size()){if(g[x+1][y+1] == 1){++nCount;};};
    if(x < g.size()){if(g[x+1][y] == 1){++nCount;};};
    if(y > g[x].size()){if(g[x][y+1] == 1){++nCount;};};
    if(x > 0 && y < g[x].size()){if(g[x-1][y+1 == 1]){++nCount;};};
    if(x < g.size() && y > 0){if(g[x+1][y-1] == 1){++nCount;};};
    return nCount;
}

grid testCell(grid g, grid gN, int x, int y)
{
    gN = g;
    auto nCount = getNeighboursCount(g, x, y);
    if(g[x][y] == 1) //1 == TRUE == alive
    {
        if(nCount == 3 || nCount == 2){gN[x][y] == 1;} //Keep status
        else
        {
            gN[x][y] = 0;
        }
    }
    else if(g[x][y] == 0)
    {
        if(nCount == 3){gN[x][y] = 1;}
        else {gN[x][y] == 0;};
    }
    return gN;
}

grid step(grid g, grid gN)
{
    for(int i = 0; i < g.size(); ++i)
    {
        for(int j = 0; j < g[i].size(); ++j)
        {
            gN = testCell(g, gN, i, j);
        }
    }
    // works fine till here...
    return gN;
}

int main()
{
    grid g =
    { ...
        // 40 times 40 grid of 0
    };
    output(g);
    string useless;
    grid gN = g;
    while(getline(cin, useless))
    {
        gN = step(g, gN);
        output(gN);
    }

}

So, when I Start the program it prints out the whole grid as it is supposed to do. But when it gets to the point where gN = step(...); I get an error. But I was able to spot that it has something to do with the return gN; statement of the swap() function.

thx for helping

You're trying to test out-of-bounds conditions inside getNeighboursCount(), but you are not doing it completely right. In lines

    if(x < g.size() && y < g[x].size()){if(g[x+1][y+1] == 1){++nCount;};};
    if(x < g.size()){if(g[x+1][y] == 1){++nCount;};};
    if(y > g[x].size()){if(g[x][y+1] == 1){++nCount;};};
    if(x > 0 && y < g[x].size()){if(g[x-1][y+1 == 1]){++nCount;};};
    if(x < g.size() && y > 0){if(g[x+1][y-1] == 1){++nCount;};};

each test for overflow (e.g. x < g.size()) is incorrect. The getNeighbourghsCount() method never gets called with an x that would not satisfy the condition, x is always smaller than the size of the container, because it's 0 based indexed. One way to fix it would be to change the condition to x < g.size() - 1

There are other problems, e.g. g[x-1][y+1 == 1] is certainly a typo. But this might get you started...