Explorations with 0 terminated buffers & strings in zig

zero_terminated_strings.zig

const std = @import("std");

fn print_string_contents(buffer: anytype) void {
    std.debug.print("string print: '{s}'\n", .{ buffer });

    std.debug.print("char print:\n", .{});
    for (buffer) |b, ind| {
        std.debug.print("  {d}: {d} {s}", .{ ind, b, buffer[ind..ind+1] });
    }

    std.debug.print("\nbuffer.len: {d}", .{ buffer.len});
    // std.debug.print("\nbuffer[buffer.len]: {d}", .{ buffer[buffer.len]});
    std.debug.print("\ndone.\n", .{});
}

fn test_buffer_type(comptime T: type) void {
    const alphabet = "abcdefghijklmnopqrstuvwxyz";

    {
        var buffer:T = .{};
        std.debug.print("\nfilled by setting array items exhaustively\n", .{});
        for (buffer) |*b, ind| {
            b.* = alphabet[ind];
        }
        print_string_contents(buffer);
    }

    {
        var buffer:T = .{};
        std.debug.print("\nfilled by memset\n", .{});
        std.mem.set(u8, &buffer, 97);
        print_string_contents(buffer);
    }

    {
        var buffer:T = .{};
        std.mem.set(u8, &buffer, 0);
        std.debug.print("\nfilled by copy\n", .{});
        const word = "hello";
        std.mem.copy(u8, &buffer, word);
        print_string_contents(buffer);
    }

    {
        var buffer:T = .{};
        std.mem.set(u8, &buffer, 1);
        std.debug.print("\nmemset to 1 filled by copy\n", .{});
        {
            const word = "no term";
            std.mem.copy(u8, &buffer, word);
            print_string_contents(buffer);
        }

        {
            std.mem.set(u8, &buffer, 1);
            const word:[:0]const u8 = "zero_term";
            std.mem.copy(u8, &buffer, word);
            print_string_contents(buffer);
        }

        {
            std.mem.set(u8, &buffer, "a"[0]);
            print_string_contents(buffer);
            const word:[:0]const u8 = "letters";

            std.mem.copy(u8, &buffer, word);
            print_string_contents(buffer);
        }
    }

}


test "0 terminated stack allocated array" {
    const bufsize:usize = 16;

    std.debug.print("\n----------------------------------------\n", .{});
    std.debug.print("[bufsize:0]u8\n", .{});
    std.debug.print("----------------------------------------\n", .{});
    test_buffer_type([bufsize:0]u8);
    // prints:
    // ----------------------------------------
    // [bufsize:0]u8
    // ----------------------------------------
    //
    // filled by setting array items exhaustively
    // string print: 'abcdefghijklmnop'
    // char print:
    //   0: 97 a  1: 98 b  2: 99 c  3: 100 d  4: 101 e  5: 102 f  6: 103 g  7: 104 h  8: 105 i  9: 106 j  10: 107 k  11: 108 l  12: 109 m  13: 110 n  14: 111 o  15: 112 p
    // buffer.len: 16
    // done.
    //
    // filled by memset
    // string print: 'aaaaaaaaaaaaaaaa'
    // char print:
    //   0: 97 a  1: 97 a  2: 97 a  3: 97 a  4: 97 a  5: 97 a  6: 97 a  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.
    //
    // filled by copy
    // string print: 'hello'
    // char print:
    //   0: 104 h  1: 101 e  2: 108 l  3: 108 l  4: 111 o  5: 0   6: 0   7: 0   8: 0   9: 0   10: 0   11: 0   12: 0   13: 0   14: 0   15: 0
    // buffer.len: 16
    // done.
    //
    // memset to 1 filled by copy
    // string print: 'no term'
    // char print:
    //   0: 110 n  1: 111 o  2: 32    3: 116 t  4: 101 e  5: 114 r  6: 109 m  7: 1   8: 1   9: 1   10: 1   11: 1   12: 1   13: 1   14: 1   15: 1
    // buffer.len: 16
    // done.
    // string print: 'zero_term'
    // char print:
    //   0: 122 z  1: 101 e  2: 114 r  3: 111 o  4: 95 _  5: 116 t  6: 101 e  7: 114 r  8: 109 m  9: 1   10: 1   11: 1   12: 1   13: 1   14: 1   15: 1
    // buffer.len: 16
    // done.
    // string print: 'aaaaaaaaaaaaaaaa'
    // char print:
    //   0: 97 a  1: 97 a  2: 97 a  3: 97 a  4: 97 a  5: 97 a  6: 97 a  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.
    // string print: 'lettersaaaaaaaaa'
    // char print:
    //   0: 108 l  1: 101 e  2: 116 t  3: 116 t  4: 101 e  5: 114 r  6: 115 s  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.

    std.debug.print("\n----------------------------------------\n", .{});
    std.debug.print("[bufsize]u8\n", .{});
    std.debug.print("----------------------------------------\n", .{});
    test_buffer_type([bufsize]u8);
    // prints:
    // ----------------------------------------
    // [bufsize]u8
    // ----------------------------------------
    //
    // filled by setting array items exhaustively
    // string print: 'abcdefghijklmnop'
    // char print:
    //   0: 97 a  1: 98 b  2: 99 c  3: 100 d  4: 101 e  5: 102 f  6: 103 g  7: 104 h  8: 105 i  9: 106 j  10: 107 k  11: 108 l  12: 109 m  13: 110 n  14: 111 o  15: 112 p
    // buffer.len: 16
    // done.
    //
    // filled by memset
    // string print: 'aaaaaaaaaaaaaaaa'
    // char print:
    //   0: 97 a  1: 97 a  2: 97 a  3: 97 a  4: 97 a  5: 97 a  6: 97 a  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.
    //
    // filled by copy
    // string print: 'hello'
    // char print:
    //   0: 104 h  1: 101 e  2: 108 l  3: 108 l  4: 111 o  5: 0   6: 0   7: 0   8: 0   9: 0   10: 0   11: 0   12: 0   13: 0   14: 0   15: 0
    // buffer.len: 16
    // done.
    //
    // memset to 1 filled by copy
    // string print: 'no term'
    // char print:
    //   0: 110 n  1: 111 o  2: 32    3: 116 t  4: 101 e  5: 114 r  6: 109 m  7: 1   8: 1   9: 1   10: 1   11: 1   12: 1   13: 1   14: 1   15: 1
    // buffer.len: 16
    // done.
    // string print: 'zero_term'
    // char print:
    //   0: 122 z  1: 101 e  2: 114 r  3: 111 o  4: 95 _  5: 116 t  6: 101 e  7: 114 r  8: 109 m  9: 1   10: 1   11: 1   12: 1   13: 1   14: 1   15: 1
    // buffer.len: 16
    // done.
    // string print: 'aaaaaaaaaaaaaaaa'
    // char print:
    //   0: 97 a  1: 97 a  2: 97 a  3: 97 a  4: 97 a  5: 97 a  6: 97 a  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.
    // string print: 'lettersaaaaaaaaa'
    // char print:
    //   0: 108 l  1: 101 e  2: 116 t  3: 116 t  4: 101 e  5: 114 r  6: 115 s  7: 97 a  8: 97 a  9: 97 a  10: 97 a  11: 97 a  12: 97 a  13: 97 a  14: 97 a  15: 97 a
    // buffer.len: 16
    // done.
}