Question

I’m trying to hide the implementation of my struct. The definitions of the struct are located in Board.h:

typedef struct Board* BoardP;
typedef const struct Board* ConstBoardP;

And i want to allocate memory as needed in Board.c:

#include <stdio.h>
#include <stdlib.h>
#include "Board.h"
#define TARGET_LENGTH 5
#define DEFAULT_BOARD_SIZE 10

 struct Board*
 newBoard(int r, int c)
{
    struct Board *b = (struct Board*) malloc(sizeof(struct Board));

     char ** array;
     int i;
     array = (char**) malloc( r*sizeof(char*) );
     for (i=0; i<r; i++)
     {
        array[i] = malloc( c*sizeof(char) );
     }
     b->_values = array;
     b->_last_player = 'X';
     b->_size_r = r;
     b->_size_c = c;
    return b;
}

But i’m getting the error:

invalid application of ‘sizeof’ to incomplete type ‘struct Board’

I’m running in circles for hours now and need someone to clear my head of the mess i’ve created. If i want to dynamically allocate memory to an array inside a struct how can i define the struct beforehand?

Answer 1

You have to define the Board structure in Board.c first:

//Board.c
struct Board {
 ....
};

Or somewhere else that is #include‘d in Board.c, anyway, the compiler needs to see its definition to determine its size when using sizeof() and to access its members. There’s an example in the Wikipedia Page too.