Getting a subroutine to return three seperate arrays of random numbers in C
I currently have code for a subroutine to return a pointer to an array. This array is a list of random numbers for a one dimensional monte-carlo integral. I am now trying to do a multi dimensional equivalent which requires 3 arrays of random numbers and instead of having a separate subroutine for each I'm trying to make one which returns a 3 by N + 1 array. Could somebody please help me with the coding for this. A mate mentioned I would need a double pointer but most web sources have been unhelpful thus far. Here is my single array code:
double* rdm_Y(void)
{
double* Random_number_list_Y = calloc(N + 1, sizeof(dou开发者_如何学JAVAble));
int i;
sleep(1);
srand(time(NULL));
for (i = 1; i <= N; i++) {
Random_number_list_Y[i] = (float) rand() / (float) RAND_MAX;
}
return Random_number_list_Y;
}
Many Thanks! Jack Medley
The general pattern for dynamically allocating a 2D array of type T (where T can be int
, double
, etc.) is
#include <stdlib.h>
T **alloc(size_t rows, size_t columns)
{
T **arr = malloc(sizeof *arr, rows); // type of *arr is T *
if (arr)
{
size_t i;
for (i = 0; i < rows; i++)
{
arr[i] = malloc(sizeof *arr[i], columns); // type of *arr[i] is T
if (arr[i])
{
size_t j;
for (j = 0; j < columns; j++)
{
arr[i][j] = initial_value_for_this_element;
}
}
}
}
return arr;
}
Try:
struct res{
double *arr1, *arr2, *arr3;
};
main(){
struct res r;
r.arr1 = rdm_Y();
r.arr2 = rdm_Y();
r.arr3 = rdm_Y();
// in r you have 3 pointers to 3 separate arrays
}
or something like this
The three methods I can think of are:
- A
*double
to a 1D array of size 3xN (you can just pretend it's three arrays) - A
**double
to an array of three*double
s, each one pointing to an array of N - A
struct
containing three*double
s, each one pointing to an array of N
If you don't like pretending for method 1 you can declare two more *double
s and set them to the return value + N and + 2N respectively. Also don't forget to free()
you should have 1, 4, and 3 free()
s to do for each of the methods respectively.
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