Yasien Yasien - 2 months ago 14
C++ Question

Dynamic Allocation using a member in a structure

I tried to allocate memory for structure members:
this is the structure:

struct conserved_variables {
double **roh;
double **mx;
double **my;
double **E;
};


I constructed an array of this structure

conserved_variables ** U= new conserved_variables*[Ny];
for (int i = 0; i < Ny; i++)
{
U[i] = new conserved_variables[Nx];
}


Then I tried to allocate arrays for each member in this structure:

for (int i = 0; i < Ny; i++)
for (int j = 0; j < Nx; j++)
{
U[i][j].E = new double*[Order + 1];
U[i][j].mx = new double*[Order + 1];
U[i][j].my = new double*[Order + 1];
U[i][j].roh = new double*[Order + 1];
for (int k = 0; k <= Order; i++)
{
U[i][j].roh[k] = new double[Order + 1];
U[i][j].mx[k] = new double[Order + 1];
U[i][j].my[k] = new double[Order + 1];
U[i][j].E[k] = new double[Order + 1];
}
}


I got this error message:

Exception thrown at 0x01153FDD in FR_1D_Advection_Equation.exe: 0xC0000005: Access violation writing location 0xCDCDCDCD.

If there is a handler for this exception, the program may be safely continued.

Answer

This is a memory locality nightmare.

As for your actual bug, you were not careful with your inner loop:

for (int k = 0; k <= Order; i++)
//                          ^
//                          you mean k

This is exploding because you accidentally push i way past the bounds of the U array. It should have been easy to spot if you had spent as much time using a debugger as it took you to ask the question on Stack Overflow.

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