#Zig style string to c string?

1 messages · Page 1 of 1 (latest)

coral dune
#

Im having issues figuring out how I can convert a []const u8 into a [*c]const u8 correctly

 var config = try Config.init(allocator);
    defer config.deinit();

    const c_token: [*c]const u8 = config.DC_TOKEN;

    const client = c.discord_init(c_token);
lyric widget
#

i think it should be coerced automatically?

fathom kite
#

given you are not also passing along the length of the string this C function likely expects the string to be null terminated, which []const u8 is not.

slim kayak
# 
const std = @import("std");

test "[]const u8 to [*c]const u8 - with terminator" {
    var arenabuf = std.heap.ArenaAllocator.init(std.testing.allocator);
    defer arenabuf.deinit();
    const arena = arenabuf.allocator();

    const raw = "hellobadbytes";
    const s1: []const u8 = raw[0..5]; // "hello"
    const s2: [*c]const u8 = try arena.dupeZ(u8, s1); // "hello\0"
    try std.testing.expectEqual(0, s2[s1.len]);
    const s3 = try std.fmt.allocPrint(arena, "{s}", .{s2}); // "hello", printing without badbytes
    try std.testing.expectEqualStrings(s1, s3);

    // other direction:
    const s4: [*c]const u8 = raw.ptr;
    const s5 = try std.fmt.allocPrint(arena, "{s}", .{s4});
    try std.testing.expectEqualStrings(raw, s5);

    // you can leave [*c]T to foreign signatures and use more restrained types
    // in your own code
    const s6: [*:0]const u8 = raw.ptr;
    const s7: [*c]const u8 = s6;
    _ = s7;
}
fathom kite
#

more important: don't use C pointers, use the correct pointer type; they will coerce to a C pointer at the translated function boundary and you can coerce a c pointer to any zig pointer type
https://github.com/ziglang/zig/issues/2984 using C pointers in not translated code will become a compile error at some point

pulsar mica
#

To add another example to this, I have the below in my code that uses SDL (a C library):

            const file_path_z = try std.fmt.allocPrint(allocator, "assets/{s}.png", .{@tagName(obj_type)});
            const file_path_c: [:0]u8 = try allocator.dupeZ(u8, file_path_z);
            defer allocator.free(file_path_z);
            defer allocator.free(file_path_c);

            const surface = c.IMG_Load(file_path_c) orelse {
                c.SDL_Log("Could not load image %s\n", c.SDL_GetError());
                return error.SDLInitFailed;
            };```
digital crow
digital crow
pulsar mica