Thread: Accessing structures value within structurepointer in 2D array

Hello!

I had no idea how to express myself in the title, but this is what I want to achieve:

Code:

typedef struct structureOne{
    struct structureTwo* aStructure;
}structureOne;


typedef struct structureTwo{
    char value;
}structureTwo;


main(){
    structureOne** 2Darray;
    //Allocate 2Darray of type structureOne
    //and give the structureTwo variable value
    //a value. Now print that value.


    //Not working
    printf("%c", 2Darray[x][y]->aStructure.value);
}

Code:

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

#define NUMROWS 5
#define NUMCOLS 10

typedef struct Data {
    char value;
} Data;

typedef struct Element {
    Data *data;
} Element;

int main(){
    Element **grid;

    // Allocate space for row pointers.
    grid = malloc(NUMROWS * sizeof(Element*));
    // Allocate space for all grid elements.
    grid[0] = malloc(NUMROWS * NUMCOLS * sizeof(Element));
    // Assign row pointers to element rows.
    for (int row = 1; row < NUMROWS; row++)
        grid[row] = grid[row-1] + NUMCOLS;

    // Allocate space for data.
    Data *data = malloc(NUMROWS * NUMCOLS * sizeof(Data));
    // Assign data to data members.
    for (int row = 0; row < NUMROWS; row++)
        for (int col = 0; col < NUMCOLS; col++)
            grid[row][col].data = data + (row * NUMCOLS + col);

    // Fill grid data values.
    for (int row = 0; row < NUMROWS; row++)
        for (int col = 0; col < NUMCOLS; col++)
            grid[row][col].data->value = 'A' + row + col;

    // Print values. 
    for (int row = 0; row < NUMROWS; row++) {
        for (int col = 0; col < NUMCOLS; col++)
            printf("%c ", grid[row][col].data->value);
        putchar('\n');
    }

    // Free all allcoated memory.
    free(grid[0]);
    free(grid);
    free(data);

    return 0;
}

Wow, that was an interesting way of creating and handling a 2D array I have never thought about it in this way. It surely seems more comfortable to maintain. Thanks! Any idea why my way didn't work?

Originally Posted by Kirderf

Any idea why my way didn't work?

You gave only the sketchiest sketch of your program (complete with illegal variable name "2DArray"), however when accessing the data you used an arrow (->) where you should have used a dot (.) and a dot where you should have used an arrow. It should be:

Code:

printf("%c", TwoDarray[x][y].aStructure->value);