为什么我在Visual Studio中遇到堆栈溢出错误

Question

I'm a beginner in C++ and don't understand many of background processes such as how compiler allocates memory etc. I'm using Visual Studio 2013 for writing c++ program. I have to use visual studio as I'm linking matlab to my c++ code.

I am getting stack overflow error which I don't know how to remove it. I don't get this error when I set N = 100, but when I set larger values of N such as 150, 200, I get the stack overflow error.

It will be really great if anyone can point out why I'm getting this error in VS. I tested the same code using codeblocks with GCC compiler which doesn't give any error at all.

#include<iostream>
using namespace std;

const int N = 200;              //Number of grid points

int main()
{

double n = N;
double dx = 4 / (n - 1); double dy = 4 / (n - 1);
double col = n, row = n;
double dt = 0.5*dx;                             // time step size(dTau)
int itmax = 2500;                               // max iterations
int i, j, t;
double x[N] = { 0.0 }, y[N] = { 0.0 };
x[0] = -2; y[0] = -2;                           // define grid
for (i = 1; i < N; i++){
    x[i] = x[i - 1] + dx;
    y[i] = y[i - 1] + dy;
}

// Initialize variables
double phi_0[N][N], phi_new[N][N],  F_0[N][N], F_new[N][N], F[N][N],
    Fext[N][N], phi[N][N];

return 0;
}

Answer 1

By default, Visual Studio creates a stack that's only a few megabytes (or maybe only one--I don't remember exactly, but typically only a small fraction of the memory on a current machine anyway). When N gets too large, you're just using more than that.

One obvious alternative is to define your large arrays as static so they won't be on the stack.

static double phi_0[N][N], phi_new[N][N],  F_0[N][N], F_new[N][N], F[N][N],
    Fext[N][N], phi[N][N];

This forces the arrays to be allocated statically. In main this makes little real difference, because main isn't allowed to be called recursively. In a function that was directly or indirectly recursive, however, this could/would cause a problem. In such a case, you'd probably want to use an std::vector instead, as this allocates (most of) its data on the free store and uses only a small, fixed amount of stack memory (typically around 12-32 bytes per vector).

Answer 2

You're allocating 7 double [N][N] variables with automatic storage duration ie on stack. A single double variable is of size 64-bits (usually) ie 8 bytes; so in total 8 * 200 * 200 * 7 = 2240000 bytes (2.13 MiB ) are required. This is probably more than the stack space allowed for a frame on your platform.

MSDN says that the default stack size is 1 MiB while you're trying to allocate more than that, hence the error.

Apart from the alternative that Jerry suggests, you also have the option of dynamic, free-store (usually on the heap) allocation, which is not limited by the stack size.