I am having trouble figuring out how to allocate memory for an array of pointers in a function. In this same function I am trying to initialize the arrays with values from another array. I have been trying different things for a while and I cannot figure out where I do and do not need.
#include <stdio.h>
#include <stdlib.h>
void allocate();
void print();
int main() {
int array_length = 10;
int array[array_length] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int **ascending;
int **descending;
allocate(&ascending, &descending, array, array_length);
print(&ascending, &descending, array, array_length);
}
void allocate(int ***ascending, int ***descending, int array[], int array_length) {
*ascending = (int **)malloc(array_length * sizeof(int *));
*descending = (int **)malloc(array_length * sizeof(int *));
int i, first_index = 0;
for (i = 0; i < array_length; i++) {
(*ascending)[i] = &(array[i]);
(*descending)[i] = &(array[i]);
}
}
void print(int **ascending, int **descending, int array[], int array_length) {
int i;
printf("\nAscending\tOriginal\tDescending\n\n");
for (i = 0; i < array_length; i++) {
printf("%d\t\t", ascending[i]);
printf("%d\t\t", array[i]);
printf("%d\t\t", descending[i]);
printf("\n");
}
printf("\n");
}
First of all, variable-size arrays cannot be initialized. You should use a MACRO for array_length
.
Then, as per your function definition, the call to print()
needs int **
as first two arguments, not int ***
. Change the function call to
print(ascending, descending, array, array_length);
also, ascending[i]
and descending[i]
, in this case, are of type int *
, you need one more level of dereference to get the int
.
That said,
void allocate();
void print();
are bad forward declarations. You should be using the exact signature of the functions for declaration and definition.
A sample working version may look like something
//gcc 4.9.3
#include <stdio.h>
#include <stdlib.h>
#define arraysize 10
void allocate(int ***ascending, int ***descending, int array[], int array_length);
void print(int **ascending, int **descending, int array[], int array_length);
int main(void) {
int array_length = arraysize;
int array[arraysize] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
int **ascending;
int **descending;
allocate(&ascending, &descending, array, array_length);
print(ascending, descending, array, array_length);
return 0;
}
void allocate(int ***ascending, int ***descending, int array[], int array_length) {
*ascending = (int **)malloc(array_length * sizeof(int *));
*descending = (int **)malloc(array_length * sizeof(int *));
int i = 0;//, first_index = 0;
for (i = 0; i < array_length; i++) {
(*ascending)[i] = &(array[i]);
(*descending)[i] = &(array[i]);
}
}
void print(int **ascending, int **descending, int array[], int array_length) {
int i;
printf("\nAscending\tOriginal\tDescending\n\n");
for (i = 0; i < array_length; i++) {
printf("%d\t\t", *(ascending[i]));
printf("%d\t\t", array[i]);
printf("%d\t\t", *(descending[i]));
printf("\n");
}
printf("\n");
}