mirror of
https://codeberg.org/andyscott/ziglings.git
synced 2024-12-22 22:13:11 -05:00
104 lines
3.5 KiB
Zig
104 lines
3.5 KiB
Zig
//
|
|
// A sentinel value indicates the end of data. Let's imagine a
|
|
// sequence of lowercase letters where uppercase 'S' is the
|
|
// sentinel, indicating the end of the sequence:
|
|
//
|
|
// abcdefS
|
|
//
|
|
// If our sequence also allows for uppercase letters, 'S' would
|
|
// make a terrible sentinel since it could no longer be a regular
|
|
// value in the sequence:
|
|
//
|
|
// abcdQRST
|
|
// ^-- Oops! The last letter in the sequence is R!
|
|
//
|
|
// A popular choice for indicating the end of a string is the
|
|
// value 0. ASCII and Unicode call this the "Null Character".
|
|
//
|
|
// Zig supports sentinel-terminated arrays, slices, and pointers:
|
|
//
|
|
// const a: [4:0]u32 = [4:0]u32{1, 2, 3, 4};
|
|
// const b: [:0]const u32 = &[4:0]u32{1, 2, 3, 4};
|
|
// const c: [*:0]const u32 = &[4:0]u32{1, 2, 3, 4};
|
|
//
|
|
// Array 'a' stores 5 u32 values, the last of which is 0.
|
|
// However the compiler takes care of this housekeeping detail
|
|
// for you. You can treat 'a' as a normal array with just 4
|
|
// items.
|
|
//
|
|
// Slice 'b' is only allowed to point to zero-terminated arrays
|
|
// but otherwise works just like a normal slice.
|
|
//
|
|
// Pointer 'c' is exactly like the many-item pointers we learned
|
|
// about in exercise 054, but it is guaranteed to end in 0.
|
|
// Because of this guarantee, we can safely find the end of this
|
|
// many-item pointer without knowing its length. (We CAN'T do
|
|
// that with regular many-item pointers!).
|
|
//
|
|
// Important: the sentinel value must be of the same type as the
|
|
// data being terminated!
|
|
//
|
|
const print = @import("std").debug.print;
|
|
|
|
pub fn main() void {
|
|
// Here's a zero-terminated array of u32 values:
|
|
var nums = [_:0]u32{ 1, 2, 3, 4, 5, 6 };
|
|
|
|
// And here's a zero-terminated many-item pointer:
|
|
var ptr: [*:0]u32 = &nums;
|
|
|
|
// For fun, let's replace the value at position 3 with the
|
|
// sentinel value 0. This seems kind of naughty.
|
|
nums[3] = 0;
|
|
|
|
// So now we have a zero-terminated array and a many-item
|
|
// pointer that reference the same data: a sequence of
|
|
// numbers that both ends in and CONTAINS the sentinel value.
|
|
//
|
|
// Attempting to loop through and print both of these should
|
|
// demonstrate how they are similar and different.
|
|
//
|
|
// (It turns out that the array prints completely, including
|
|
// the sentinel 0 in the middle. The many-item pointer stops
|
|
// at the first sentinel value.)
|
|
printSequence(nums);
|
|
printSequence(ptr);
|
|
|
|
print("\n", .{});
|
|
}
|
|
|
|
// Here's our generic sequence printing function. It's nearly
|
|
// complete, but there are a couple missing bits. Please fix
|
|
// them!
|
|
fn printSequence(my_seq: anytype) void {
|
|
const my_type = @typeInfo(@TypeOf(my_seq));
|
|
|
|
// The TypeInfo contained in my_type is a union. We use a
|
|
// switch to handle printing the Array or Pointer fields,
|
|
// depending on which type of my_seq was passed in:
|
|
switch (my_type) {
|
|
.Array => {
|
|
print("Array:", .{});
|
|
|
|
// Loop through the items in my_seq.
|
|
for (???) |s| {
|
|
print("{}", .{s});
|
|
}
|
|
},
|
|
.Pointer => {
|
|
// Check this out - it's pretty cool:
|
|
const my_sentinel = my_type.Pointer.sentinel;
|
|
print("Many-item pointer:", .{});
|
|
|
|
// Loop through the items in my_seq until we hit the
|
|
// sentinel value.
|
|
var i: usize = 0;
|
|
while (??? != my_sentinel) {
|
|
print("{}", .{my_seq[i]});
|
|
i += 1;
|
|
}
|
|
},
|
|
else => unreachable,
|
|
}
|
|
print(". ", .{});
|
|
}
|