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carrayspointersfreedouble-pointer
user3440489
user3440489

Reputation: 259

Free a double pointer in C

I have two functions to create arrays.

double *Array1D (int nx, int dsize) {
  double *v;
  v = calloc(nx, dsize);
  return v;
}

double **Array2D (int ny, int nx, int dsize) {
  double **v; int j;
  for (j = 0; j < ny; j++)
    v[j] = Array1D(nx, dsize);
  return v;
}

int i, j;
pn = Array2D (ny, nx, sizeof(double));
for (j = 0; j < ny; j++)
  for (i = 0; i < nx; i++)
    pn[j][i] = 1.0 + (i + j * nx) * 1.0;

for (i = 0; i < ny; i++)
  free(pn[i]);
free(pn);

The array elements get initialized properly, but freeing them creates a segmentation fault.

Error: 

*** glibc detected *** ./array_test: free(): invalid pointer: 0x00007fff00d42a4f ***
Segmentation fault (core dumped)

Upvotes: 2

Views: 560

Answers (4)

Gopi
Gopi

Reputation: 19864

The order of allocation is

v = malloc(sizeof(double *) * ny);
for (j=0; j<ny; j++) v[j] = Array1D(nx, dsize);

The order of freeing is

for (j=0; j<ny; j++)
free(v[j]);

free(v);

Upvotes: 3

wolfPack88
wolfPack88

Reputation: 4203

You never allocate memory for your 2d array. You need a line v = malloc(sizeof(double *) * ny); right before your for loop in double **Array2D(int ny, int nx, int dsize);

Upvotes: 4

Quentin
Quentin

Reputation: 63124

double **Array2D (int ny, int nx, int dsize) {
    double **v; int j;
    for (j=0; j<ny; j++) v[j] = Array1D(nx, dsize);
    return v;
}

You forgot to allocate *v.

Upvotes: 2

ouah
ouah

Reputation: 145829

double **Array2D (int ny, int nx, int dsize)
{
  double **v; int j;
  for (j=0; j<ny; j++) v[j] = Array1D(nx, dsize);

v object is never initialized in your function.

Upvotes: 5

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