How to avoid unsigned values error in zig?

Question

I have the following code

const std = @import("std");
const stdio = @cImport({
    @cInclude("stdio.h");
});

const ioctl = @cImport({
    @cInclude("sys/ioctl.h");
    @cInclude("stdio.h");
    @cInclude("unistd.h");
    @cInclude("errno.h");
    @cInclude("termios.h");
});


pub fn main() !void {

    var t = ioctl.termios {

    };

    const is_terminal = ioctl.ioctl(0, ioctl.TIOCGETA, t);
    if (is_terminal == 0) {
        t.c_iflag &= @intCast(@as(c_long, @intCast(~(ioctl.IGNBRK
            | ioctl.BRKINT
            | ioctl.PARMRK
            | ioctl.ISTRIP
            | ioctl.INLCR
            | ioctl.IGNCR
            | ioctl.ICRNL
            | ioctl.IXON))));

        t.c_oflag &= ~ioctl.OPOST;
        t.c_lflag &= ~(ioctl.ECHO | ioctl.ECHONL | ioctl.ICANON | ioctl.ISIG | ioctl.IEXTEN);
        t.c_cflag &= ~(ioctl.CSIZE | ioctl.PARENB);
        t.c_cflag |= ioctl.CS8;
        t.c_cc[ioctl.VMIN] = 1;
        t.c_cc[ioctl.VTIME] = 0;


        ioctl.ioctl(0, ioctl.TIOCSETA, t);
    }



    std.debug.print("Hello {any}.", .{ is_terminal });
}

The goal is to put the terminal into raw mode. Problem is: I can't make zig accept the code. I've done the same call in Java through jextract generated code so I know its right (or should be). Is there something I am missing?

main.zig:46:31: error: type 'c_ulong' cannot represent integer value '-1004'
        t.c_iflag &= @intCast(@as(c_long, @intCast(~(ioctl.IGNBRK
                              ^~~
referenced by:
    main: /Users/emccue/Library/zig/0.15.0-dev.375+8f8f37fb0/lib/std/start.zig:671:37
    comptime: /Users/emccue/Library/zig/0.15.0-dev.375+8f8f37fb0/lib/std/start.zig:58:30
    2 reference(s) hidden; use '-freference-trace=4' to see all references

sigod · Accepted Answer · 2025-04-20 18:57:46Z

0

I believe you're looking for @bitCast instead of @intCast.

answered Apr 20 at 18:57

sigod

6,7652 gold badges28 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Ethan McCue Apr 20 at 19:07

That gets me a different error ``` main.zig:46:35: error: @bitCast size mismatch: destination type 'c_ulong' has 64 bits but source type 'c_int' has 32 bits t.c_iflag &= @as(c_ulong, @bitCast(~(ioctl.IGNBRK ^~~~~~~~ ```

sigod Apr 20 at 19:49

@EthanMcCue It works for me for what I've tried. Can you create a minimal reproducible example and attach it to the question?

cafce25 · Accepted Answer · 2025-05-18 07:52:04Z

0

If you have a positive number on a signed int.

const i: i32 = 123;

~i will be negative.

assert(~i < 0)

this could be solved with a @bitCast() since @intCast() does not allow to change the sign.

const u: u32 = @bitCast(~i)

The second problem is that c_ulong and c_int have different bitsizes

@bitCast only works if they have the same size.

You can either:

First use @intCast() and then use ~ that way you don't cast a negative number.
or use a @bitCast() to change the type from c_int to c_uint. and then use intCast() from c_uint to c_ulong.

edited May 18 at 7:52

cafce25

29.9k5 gold badges49 silver badges68 bronze badges

answered May 17 at 14:46

Emmmmllll

213 bronze badges

Collectives™ on Stack Overflow

How to avoid unsigned values error in zig?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related