memory problem on 3D array - segmentation fault

[gipark]

I want to make a big 3D array called u3d,

so I declared it with the following sentence:
nx=4096;
ny=400;
nz=129;
double u3d[nx][ny][nz];


C++ repeatedly gives the following error message:
/bin/sh: line 1: 4587 Segmentation fault

If I set nx up to 30, it's OK, but if nx is greater than 30,
segmentation fault messages occur.

Am I using a too big array to handle in my system?
I cannot understand since in Fortran there was no problem with the following
command:
real, allocatable, dimension(:,:,:) :: u3d
allocate(u3d(1:nx,1:ny,1:nz))

[S6k9GNh0]

Allocate it on heap via the new operator. The array is too large for the stack:

double *u3d = new double[nx][ny][nz]

Also, using variables to specify the size of stack arrays should be illegal. NOTE: Though GCC allows it, it still warns you as it isn't a flexible method of allocation and will not compile on any others. GCC is breaking the specification at the users expense which most do not.

[iharrold]

Dynamically allocate the array. Depending upon the OS you'll have compile time allocation size issues.

double *** u3d;

u3d = new double ** [nx];
if (NULL = u3d)
   //Handle error;
else
{
  for (int i = 0; i < nx; i++)
  {
     u3d[i] = new double *[ny];
     if (NULL == u3d[i])
     {
         //Handle Error
         //and unwind the allocations
     }
     else
     {
        for (int j = 0; j < ny; j++)
        {
           u3d[i][j] = new double [nz];
           if (NULL = u3d[i][j])
           {
               //Handle Error
               //and unwind the allocations
           }
        }
     }
  }
}

You'll also need to deallocate when finished using

for (int i = 0; i < nx; i++)
{
   for (int j = 0; j < ny; j++)
   {
       delete [] u3d[i][j];
   }
   delete [] u3d[i]
}
delete [] u3d;

Or something similar. Didn't compile this.