C named primitive types (ADR-0086)

[10.3:1]

The C named primitive types are thirteen built-in type names introduced by ADR-0086: c_schar, c_short, c_int, c_long, c_longlong, c_uchar, c_ushort, c_uint, c_ulong, c_ulonglong, c_float, c_double, and c_void. They are gated behind the c_ffi_extras preview feature.

[10.3:2]

The twelve arithmetic C named types are target-resolved. On every currently-blessed target (x86_64-unknown-linux-gnu, aarch64-unknown-linux-gnu, aarch64-apple-darwin — all LP64), the resolutions are:

Gruel type	C type	Width (bits)	Signed
`c_schar`	`signed char`	8	yes
`c_uchar`	`unsigned char`	8	no
`c_short`	`short`	16	yes
`c_ushort`	`unsigned short`	16	no
`c_int`	`int`	32	yes
`c_uint`	`unsigned int`	32	no
`c_long`	`long`	64	yes
`c_ulong`	`unsigned long`	64	no
`c_longlong`	`long long`	64	yes
`c_ulonglong`	`unsigned long long`	64	no
`c_float`	`float`	32	—
`c_double`	`double`	64	—

[10.3:3]

Each C named arithmetic type is distinct from every native Gruel arithmetic type and from every other C named type. A value of one cannot appear in a context that expects another without an explicit as conversion.

[10.3:4]

Integer literals coerce to a C named integer type when the context fixes one (for example a let annotation or a function return type). Float literals coerce to c_float or c_double analogously. The literal must fit the target-resolved width of the type.

[10.3:5]

All twelve C named arithmetic types are permitted across the FFI boundary (parameters of, and returns from, @mark(c) fn declarations and items inside link_extern blocks).

[10.3:6]

c_void is an incomplete type. It has no values, no size, and no alignment. A c_void name is well-formed only when it appears as the pointee of Ptr(c_void) or MutPtr(c_void). Bare c_void as the type of a let binding, function parameter, function return, struct field, or enum variant field is a compile-time error.

[10.3:7]

Ptr(c_void) and MutPtr(c_void) are permitted across the FFI boundary and elsewhere a raw pointer type is allowed. They correspond to C const void * and void *, respectively.

[10.3:8]

link_extern("c") {
    fn abs(x: c_int) -> c_int;
    fn malloc(size: usize) -> MutPtr(c_void);
    fn free(p: MutPtr(c_void)) -> ();
}

fn main() -> i32 {
    let x: c_int = 42;
    let p: MutPtr(c_void) = malloc(64);
    free(p);
    let y: c_int = abs(x);
    0
}