Getting a substring of a string?

[limber spade]

I'd like to get a substring of a string, i.e. the characters contained between two indexes. I tried to slice it, but since the original string is an array this doesn't work and gives error: expected type '*const [0:0]u8', found '[]const u8'.

Basically I'd like to do what this library does, but with a regular string: https://github.com/JakubSzark/zig-string/blob/e842e89f2c18eecda2721f4a3114f63c98bd5b87/zig-string.zig#L371-L387

Here is my code:

const std = @import("std");
const MAX_SUB_DIRS = 10;

pub fn main() !void {
    const out = std.io.getStdOut().writer();

    const input_cur_dir = try std.fs.cwd().openDir("input", .{});
    const file = try input_cur_dir.openFile("day07.txt", .{});
    defer file.close();

    var buffer: [100]u8 = undefined;
    var output: ?[]const u8 = try nextLine(file.reader(), &buffer);
    var cur_dir = "";
    var buf: [100]u8 = undefined;
    var fba = std.heap.FixedBufferAllocator.init(&buf);

    while (output != null) : (output = try nextLine(file.reader(), &buffer)) {
        if (output.?[0] == '$') {
            if (output.?[2] == 'c') {
                if (output.?[5] == '.') {
                    const index = std.mem.lastIndexOf(u8, cur_dir, "/").?;
                    cur_dir = cur_dir[0..index];
                } else if (output.?[5] == '/') {
                    cur_dir = "";
                } else {
                    const dir = output.?[5..output.len];
                    const to_concat: []const []const u8 = [_][]u8{ cur_dir, "/", dir };
                    cur_dir = std.mem.concat(fba.allocator(), u8, &to_concat);
                }
            }
        } else {
            // sum file sizes
        }
    }

    try out.print("Answer: TODO\n", .{});
}

pub fn nextLine(reader: anytype, buffer: []u8) !?[]u8 {
    // omitted due to character limit
}

[silver bear]

just give it an explicit tyoe

i.e. var cur_dir: []const u8 = "";

the thing is, string literals are pointers to arrays

it just happens that they coerce to slices

[limber spade]

Ah, that did it. Thanks!

[silver bear]

just so you know, a better way of doing this would be

while (try nextLine(file.reader(), &buffer)) |out| {
    if (out[0] == '$') {
        // -- snip --
    }
}

the while loop will continue for as long as the result of the try nextLine call returns non-null