Basic types

#include <libcork/core.h>

The types in this section ensure that the C99 integer types are available, regardless of platform. We also define some preprocessor macros that give the size of the non-fixed-size standard types. In addition, libcork defines some useful low-level types:

• Network addresses
• High-precision timestamps
• Hash values

Integral types

bool

A boolean. Where possible, we simply include <stdbool.h> to get this type. It might be typedefed to int. We also make sure that the following constants are defined:

bool false

bool true

int8_t

uint8_t

int16_t

uint16_t

int32_t

uint32_t

int64_t

uint64_t

Signed and unsigned, fixed-size integral types.

intptr_t

uintptr_t

Signed and unsigned integers that are guaranteed to be big enough to hold a type-cast void *.

size_t

An unsigned integer big enough to hold the size of a memory object, or a maximal array index.

ptrdiff_t

A signed integer big enough to hold the difference between two pointers.

Size macros

CORK_SIZEOF_SHORT

CORK_SIZEOF_INT

CORK_SIZEOF_LONG

CORK_SIZEOF_POINTER

The size (in bytes) of the short, int, long, and void * types, respectively.

Embedded structs

Quite often a callback function or API will take in a pointer to a particular struct, with the expectation that you can embed that struct into some other type for extension purposes. Kind of a bastardized subclassing mechanism for C code. The doubly-linked list module is a perfect example; you’re meant to embed cork_dllist_item within the linked list element type. You can use the following macro to obtain the pointer to the containing (“subclass”) struct, when given a pointer to the contained (“superclass”) struct:

struct_type *cork_container_of(field_type *field, TYPE struct_type, FIELD field_name)

The struct_type parameter must be the name of a struct type, field_name must be the name of some field within that struct, and field must be a pointer to an instance of that field. The macro returns a pointer to the containing struct. So, given the following definitions:

struct superclass {
    int  a;
};

struct subclass {
    int  b;
    struct superclass  parent;
};

struct subclass  instance;

then the following identity holds:

cork_container_of(&instance.parent, struct subclass, parent) == &instance

Note

When the superclass struct appears as the first element of the subclass struct, you can obtain the same effect using a simple type-cast. However, the cork_container_of macro is more robust, since it also works when the superclass struct appears later on in the subclass struct.