3d dimensional array with malloc and calloc? - c

Question

I am trying to make an arrangement with dynamic memory, 3-dimensional, my code is as follows:
typedef unsigned char matrix;
matrix ***mat(int n, int b)
{
matrix ***temp = (matrix ***)malloc(n*sizeof(matrix**));
for(int i=0; i<n; i++)
{
temp[i] = (matrix **)malloc(b*sizeof(matrix *));
for(int j = 0; j < b; j++)
temp[i][j]= (matrix *)malloc(b*sizeof(matrix));
}
return temp;
}
int main()
{
matrix ***M2 = mat(3,2);
for(int i=0; i<3; i++)
{
for(int j=0; j<2; j++)
{
for(int k=0; k<2; k++)
{
printf(" %d", M2[i][j][k]);
}
printf("\n");
}
printf("\n");
}
return 0;
}
when I run the program I have a segment violation, someone can tell me what the error is, since I can not visualize

Answer 1

I guess in the most nested for loop (the j one) the variables are messed in declaration for(int j = 0; i < b; i++). Try j for all

Answer 2

Usually I will do this kind of thing in FORTRAN, personally I like write the algorithm involving high dimensional array in FORTRAN as a library, and do the flow control staff in C. While 3D is still easily manageable in C, you need really careful with the pointers, here is a working example, it's valgrind clean.
#include <stdio.h>
#include <stdlib.h>
float ***myarray(int l, int m, int n)
{
float **ptr = malloc(sizeof(float*)*(l+l*m));
float *data = malloc(sizeof(float)*l*m*n);
float **p1 = ptr, **p2 = ptr+l;
for(int i=0; i<l; i++) {
p1[i] = (float*)(p2+i*m);
for(int j=0; j<m; j++)
p2[i*m+j] = data+(i*m+j)*n;
}
return (float***)ptr;
}
void myfree(float ***a)
{
free(a[0][0]);
free(a);
}
int main()
{
float ***array = myarray(4,3,2);
for(int i=0; i<4; i++)
for(int j=0; j<3; j++)
for(int k=0; k<2; k++)
array[i][j][k] = i+j+k;
myfree(array);
return 0;
}

Answer 3

you must correct the j counter inside the nested for loop in mat function, this is the correct one:
for(int j = 0; j < b; j++)