Arrays

[TheGreekMan2000]

How do I make a dynamic 2d array in C with malloc realloc and free?

[Zeus_]

(1) You can google to find out.

(2) You can use a 1D array (as 2D arrays and 1D arrays are fundamentally the same thing). You just need to do access arithmetic yourself, which is not something hard.

(3) You can use an array of pointers and allocate memory of appropriate size for each.

(4) You can use a double pointer method which is similar to using (2) and (3) together.

I don't know of any other methods, if any.

[Salem]

The malloc and free of arrays, in various ways.

#include <stdio.h>
#include <stdlib.h>

void f1(void) {
  int a[10];
  int *b = malloc(10*sizeof(*b));
  ///
  free(b);
}

// If the minor dimension is always fixed
void f2(void) {
  int a[10][20];
  int (*b)[20] = malloc(10*sizeof(*b));
  ///
  free(b);
}

// variable in both dimensions
void f3(void) {
  int a[10][20];
  int **b = malloc(10*sizeof(*b));
  for( int i = 0 ; i < 10 ; i++ )
    b[i] = malloc(20*sizeof(*b[i]));
  ///
  for ( int i = 0 ; i < 10 ; i++ )
    free(b[i]);
  free(b);
}

// variable in both dimensions, but all rows the same
void f4(void) {
  int a[10][20];
  int **b = malloc(10*sizeof(*b));
  b[0] = malloc(10*20*sizeof(*b[0]));
  for( int i = 1 ; i < 10 ; i++ )
    b[i] = b[i-1] + 20;
  ///
  free(b[0]);
  free(b);
}

int main ( ) {
  f1();
  f2();
  f3();
  f4();
}