Using sizeof() with pointer to struct in C

Question

I'm learning C right now and came to a little problem I encountered while trying out some code snippets from my uni course.

It's about typedef'd pointers to structs and their usage in the sizeof() function.

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

// Define struct
struct IntArrayStruct
{
  int length;
  int *array;
};
// Set typedef for pointer to struct
typedef struct IntArrayStruct *IntArrayRef;

// Declare function makeArray()
IntArrayRef makeArray(int length);

// Main function
int main(void)
{
  // Use makeArray() to create a new array
  int arraySize = 30;
  IntArrayRef newArray = makeArray(arraySize);
}

// Define makeArray() with function body
IntArrayRef makeArray(int length)
{
  IntArrayRef newArray = malloc(sizeof(*IntArrayRef)); // ERROR
  newArray->length = length;
  newArray->array = malloc(length * sizeof(int));
  return newArray;
}

And the code really works in the IDE used in class (Virtual C), but when I try the exact same example in VSCode and compile it using GNU Make or GCC, it returns an error because sizeof(*IntArrayRef) in the malloc() function call is marked as an unexpected type name.

error: unexpected type name 'IntArrayRef': expected expression

However, when I change it to sizeof(IntArrayStruct), everything works splendidly.

Isn't *IntArrayRef the same value as IntArrayStruct?

Answer 1

IntArrayRef is the name of a type, therefore *IntArrayRef is invalid syntax. What you can (and should) do instead is give the name of the variable and dereference that:

IntArrayRef newArray = malloc(sizeof(*newArray));