Code snippets:sizeof malloc

From C

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

#define Stringify_(x_) # x_
#define Stringify(x_) Stringify_(x_)

#define test(x_) ( \
    printf("%s: '%s'\n", (x_) ? "True" : "False", Stringify(x_)) \
  )

/* Choose your base type, here */
typedef int sometype;

/*
 * 'sizeof' is an operator, not a function.
 * The 'sizeof' operator has two forms:

  sizeof unary-expression
  sizeof (type-name)

 * if you use a 'type-name', it must be enclosed by
 * parentheses.  If you use a 'unary-expression',
 * such as a constant value or the value of an object,
 * then the parentheses can be omitted.
 *
 * The 'sizeof' operator will only perform evaluation
 * on its operand if the operand type is a variable
 * length array type: An array whose count of elements
 * is not known when the program is compiled, but only
 * at run-time.
 */

int main(void) {
    sometype ***** foo;

    /* See how a '*' on the left corresponds to one less on the right */
    test(sizeof foo == sizeof (sometype *****));
    test(sizeof *foo == sizeof (sometype ****));
    test(sizeof **foo == sizeof (sometype ***));
    test(sizeof ***foo == sizeof (sometype **));
    test(sizeof ****foo == sizeof (sometype *));
    test(sizeof *****foo == sizeof (sometype));

    /*
     * Suppose that you used the pattern

    foo = malloc(sizeof (sometype ****));

     * for each of the allocations, below.
     * Then suppose you change your mind and want to
     * use a different type than 'sometype'.  You would
     * have to change every line.  If you use the
     * pattern below, you only have to change line 34!
     */

    foo = malloc(sizeof *foo);
    if (!foo) return EXIT_FAILURE;

    *foo = malloc(sizeof **foo);
    if (!*foo) return EXIT_FAILURE;

    **foo = malloc(sizeof ***foo);
    if (!**foo) return EXIT_FAILURE;

    ***foo = malloc(sizeof ****foo);
    if (!***foo) return EXIT_FAILURE;

    ****foo = malloc(sizeof *****foo);
    if (!****foo) return EXIT_FAILURE;

    *****foo = 42;
    test(*****foo == 42);

    free(****foo);
    free(***foo);
    free(**foo);
    free(*foo);
    free(foo);

    return EXIT_SUCCESS;
  }