How to return a 2D array from a function in C?

Thank you all for your answers and more specifically for the detailed explanation of the array-pointer relationship.

I encapsulated the array in a structure

 struct point_group1 {
        float x[3];
        float y[3];
};

struct point_group1 pixels(){
    struct point_group1 temp;

    temp.x[0] = 0.0;
    temp.x[1] = 1.0;
    temp.x[2] = -1.0;

    temp.y[0] = 0.0;
    temp.y[1] = 1.0;
    temp.y[2] = 1.0;

    return temp;    
}



struct point_group1 points1  = pixels();
axPoly(points1.x, points1.y ,3, 0.0);

In C, pointers and arrays are closely related. Also, you usually need to pass the size of an array as a separate variable. Let's start you with:

#include <stdio.h>

float** createArray(int m, int n)
{
    float* values = calloc(m*n, sizeof(float));
    float** rows = malloc(m*sizeof(float*));
    for (int i=0; i<m; ++i)
    {
        rows[i] = values + i*n;
    }
    return rows;
}

void destroyArray(float** arr)
{
    free(*arr);
    free(arr);
}

void drawLine(const float** coords, int m, int n);

int main(void)
{
    float** arr = createArray(2,2);
    arr[0][0] = 1;
    arr[0][1] = 1;
    arr[1][0] = 2;
    arr[1][1] = 2;
    drawLine(arr, 2, 2); 
    destroyArray(arr);
}

In C/C++, when you pass an array to a function, it decays to be a pointer pointing to first element of the array. So, in pixels() function, you are returning the address of a stack allocated variable. The returning variable's address is no longer valid because on pixels() return, the stack allocated variable goes out of scope. So, instead you should for a variable whose storage is dynamic ( i.e., using malloc, calloc ).

So, for a two dimensional array, you may use float** arrayVariable;. Also, if you passing this to a function, you should be wary of how many rows & columns it has.

int rows, columns;

float** pixels()
{
    // take input for rows, columns
    // allocate memory from free store for the 2D array accordingly
    // return the array
}

void drawLine( float** returnedArrayVariable )
{
  //drawing the line
}

Since, 2D array is managing resources it self, it should return the resources back to the free store using free.