到目前為止已經把基本的型別都介紹完了,這篇來介紹一下進階的型別用法。
packed
packed
在 C 中不是標準的關鍵字,但是大多數的編譯器都有支援相關的擴充語法。在 Zig 中你可以直接使用 packed
來達成,改變型別的對齊行為。
union
const print = @import("std").debug.print;
const Packed = packed union { a: u32, b: f32, c: bool };const Unpacked = union { a: u32, b: f32, c: bool };
pub fn main() void { print("Packed size: {} byte\n", .{@sizeOf(Packed)}); print("Unpacked size: {} byte", .{@sizeOf(Unpacked)});}
Packed size: 4 byteUnpacked size: 8 byte
struct
const print = @import("std").debug.print;
const Packed = packed struct { bit0: u1, bit1: u1, bit2: u1, bit3: u1, bit4: u1, bit5: u1, bit6: u1, bit7: u1,};
const Unpacked = struct { bit0: u1, bit1: u1, bit2: u1, bit3: u1, bit4: u1, bit5: u1, bit6: u1, bit7: u1,};
pub fn main() void { print("Packed size: {} byte\n", .{@sizeOf(Packed)}); print("Unpacked size: {} byte", .{@sizeOf(Unpacked)});}
Packed size: 1 byteUnpacked size: 8 byte
bit-field
Zig 的 struct
並不直接支援像 C 那樣的 bit field 語法,但是你可以透過它的自訂長度整數和 packed
來完成。
轉型時可以利用 @bitCast()
。
const print = @import("std").debug.print;
const BitField = packed struct { bit0: u1, bit1: u1, bit2: u1, bit3: u1, bit4: u1, bit5: u1, bit6: u1, bit7: u1,};
const Register = union { bits: BitField, byte: u8,};
pub fn main() void { const reg = Register{ .byte = 0xA4 }; const bits: BitField = @bitCast(reg.byte);
print("0x{x} = {}{}{}{} {}{}{}{}", .{ reg.byte, bits.bit7, bits.bit6, bits.bit5, bits.bit4, bits.bit3, bits.bit2, bits.bit1, bits.bit0, });}
0xa4 = 1010 0100
另一種:
const print = @import("std").debug.print;
const BitField = packed struct { bit0: u1, bit1: u1, bit2: u1, bit3: u1, bit4: u1, bit5: u1, bit6: u1, bit7: u1,};
const Register = union { bits: BitField, byte: u8,};
pub fn main() void { const bits = BitField{ .bit0 = 0, .bit1 = 0, .bit2 = 1, .bit3 = 0, .bit4 = 0, .bit5 = 1, .bit6 = 0, .bit7 = 1, };
const reg = Register{ .bits = bits }; const byte_value: u8 = @bitCast(reg.bits);
print("0x{x}", .{byte_value});}
0xa4
匿名 struct
如果你需要一個臨時的 struct
,則可以使用匿名 struct
,例如想要一個多回傳值的函式。
const print = @import("std").debug.print;
pub fn main() void { const point = struct { x: i16, y: i16 }{ .x = 100, .y = -10 }; print("X: {}, Y: {}", .{ point.x, point.y });}
X: 100, Y: -10
參考
- packed union: Documentation - The Zig Programming Language
- packed struct: Documentation - The Zig Programming Language
- Anonymous Struct: Documentation - The Zig Programming Language
- Anonymous Structs | zig.guide
本文以 Zig 0.13.0
為主。並同時發佈在: