Allocating space for pointers to struct

Question

In another post link text

I am trying to do the same thing with a struct, but I have a problem with my sizeof operator, so in the integer case, I did this:

size_t totalMem = rows * sizeof(int *) + rows * cols * sizeof(int));

And in the struct case I did this:

size_t totalMem = (rows * sizeof(struct TEST *)) + (rows * cols * sizeof(struct TEST));

But I get the error: Invalid application of sizeof to incomplete type of struct TEST.

Any thoughts? Thanks.

Answer 1

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

#include "C2_Assignment_5_Exercise_2_Driver.h"

as part of my size_t statement. And then the definition in the .h file is:

#ifndef C2_ASSIGNMENT_5_EXERCISE_2_DRIVER_H
#define C2_ASSIGNMENT_5_EXERCISE_2_DRIVER_H

typedef struct
{
   char charObj;
   short shortObj;
   long longObj;
   double doubleObj;
} TEST;

#endif

Answer 2

Because you're defining the struct as

 typedef struct { ... } TEST;

you should always refer to the struct as TEST, not struct TEST, i.e. use

 size_t totalMem = (rows * sizeof(TEST*)) + (rows * cols * sizeof(TEST));

To use struct TEST you need to actually name the struct, i.e.

 struct TEST { ... };

You can allow both with

 typedef struct TEST { ... } TEST;

Answer 3

Change:

typedef struct MYTEST
{
   char charObj;
   short shortObj;
   long longObj;
   double doubleObj;
} TEST;

and

size_t totalMem = (rows * sizeof(struct TEST *)) + (rows * cols * sizeof(struct TEST));

to

size_t totalMem = (rows * sizeof(struct MYTEST *)) + (rows * cols * sizeof(struct MYTEST));