4.3. Simple Type Structs

C libraries often define new types for numeric handles, sizes and offsets. To translate these to a VAPI file, just use the SimpleType attribute with a struct and inherit from the same simple type in the C header.

An example:

typedef uint32_t people_inside;

would be defined in the VAPI file as:

[SimpleType]
[CCode (cname = "people_inside", has_type_id = false)]
public struct PeopleInside : uint32 {
}

When inheriting from an existing type, all the methods will be carried forward. For sizes and offsets, this is probably desirable; for handles, it is probably not. For example, a UNIX file descriptor is stored in an integer, but adding or multiplying two file handles has no sense. In this case, it is preferable not to inherit from a numeric type and add the attribute IntegerType (rank=X) so the Vala compiler can automatically cast a type into an integer of an appropriate size when needed (e.g., initialising from an integral constant).

An example from XCB:

typedef uint32_t xcb_atom_t;

would be defined in the VAPI file as:

[SimpleType]
[IntegerType (rank = 9)] 
[CCode (cname ="xcb_atom_t", has_type_id = false)] 
public struct AtomT {
    //...
}

The ranks for the common types, as defined in the glib-2.0.vapi and posix.vapi files, are:

Rank	Types in glib-2.0	Other Use
1	gint8 gfloat
2	gchar gdouble
3	guchar guint8	Posix.cc_t
4	gshort gint16
5	gushort guint16
6	gint gint32	Posix.pid_t
7	guint guint32 gunichar	Posix.speed_t Posix.tcflag_t
8	glong gssize time_t	Posix.clock_t
9	gulong gsize	Posix.nfds_t Posix.key_t Posix.fsblkcnt_t Posix.fsfilcnt_t Posix.off_t Posix.uid_t Posix.gid_t Posix.mode_t Posix.dev_t Posix.ino_t Posix.nlink_t Posix.blksize_t Posix.blkcnt_t
10	gint64
11	guint64