# Error when using \`discardRemaining()\` **URL:** \ **Category:** Help\ **Tags:** standard-library, io\ **Created:** [October 9, 2026, 6:38am UTC](https://ziggit.dev/t/error-when-using-discardremaining/17898 "2026-10-09T06:38:18Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![nrv30](https://ziggit.dev/user_avatar/ziggit.dev/nrv30/32/10025_2.png) [@nrv30](https://ziggit.dev/u/nrv30)\ **Post date:** [October 9, 2026, 6:38am UTC](https://ziggit.dev/t/error-when-using-discardremaining/17898/1 "2026-10-09T06:38:18Z")
Hi I’m a complete beginner in zig. I’m trying to make a simple REPL program but I’m running into an error when I use the discardRemaining() function for the reader. I’m looking for some help to get it working, I have provided the code and a stacktrace below. ```zig var should_quit: bool = false; while (!should_quit) { try stdout_writer.writeAll(">>> "); try stdout_writer.flush(); const input = stdin_reader.takeDelimiterExclusive('\n') catch |err| switch (err) { error.EndOfStream => { return err; }, error.ReadFailed => { return err; }, error.StreamTooLong => { // I think this is the only one I want to handle? try stdout_writer.writeAll("useful message\n"); try stdout_writer.flush(); const thing: usize = try stdin_reader.discardRemaining(); std.debug.print("{d}\n", .{thing}); continue; }, }; stdin_reader.toss(1); const trimmed_input = std.mem.trim(u8, input, " \n\r\t"); const is_equal = std.mem.eql(u8, trimmed_input, "exit"); if (is_equal) { should_quit = true; } } ``` The reason why I’m using this function is to get rid of the leftovers of what the user typed if a StreamTooLong error is reached. I’m getting this stacktrace, but I’m not sure what the problem is. It looks like maybe it’s a bug in the version of the compiler for Windows? However I don’t want to jump the gun by making an issue if I’m totally wrong. ```zig error.Unexpected NTSTATUS=0xc0000010 (INVALID_DEVICE_REQUEST) C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\Threaded.zig:1462:40: 0x7ff652e10509 in unexpectedNtstatus (int_converter_zcu.obj) return windows.unexpectedStatus(status); ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\Threaded.zig:4078:58: 0x7ff652e76b70 in fileStatWindows (int_converter_zcu.obj) else => |s| return syscall.unexpectedNtstatus(s), ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\File.zig:142:30: 0x7ff652d8a945 in stat (int_converter_zcu.obj) return io.vtable.fileStat(io.userdata, file); ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\File\Reader.zig:118:24: 0x7ff652d8a59a in getSize (int_converter_zcu.obj) if (r.file.stat(r.io)) |st| { ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\File\Reader.zig:306:35: 0x7ff652d8b64e in discard (int_converter_zcu.obj) const size = r.getSize() catch { ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\Io\Reader.zig:278:35: 0x7ff652eaf18f in discardRemaining (int_converter_zcu.obj) offset += r.vtable.discard(r, .unlimited) catch |err| switch (err) { ^ C:\Users\nirva\proj\zig\int-converter\src\main.zig:56:71: 0x7ff652ea81f0 in main (int_converter_zcu.obj) const thing: usize = try stdin_reader.discardRemaining(); ^ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\start.zig:827: 0x7ff652ea8610 in callMain (int_converter_zcu.obj) return wrapMain(root.main(.{ C:\Users\nirva\software\zig-x86_64-windows-0.17.0\zig-x86_64-windows-0.17.0\lib\std\start.zig:576:17: 0x7ff652ea8610 in WinStartup (int_converter_zcu.obj) callMain(std.os.windows.peb().ProcessParameters.CommandLine.slice(), .global), ^ ???:?:?: 0x7ffc9779cd86 in ??? (KERNEL32.DLL) ???:?:?: 0x7ffc9936caeb in ??? (ntdll.dll) ``` I’m open to any advice on how to fix it, maybe there’s a much better way to accomplish this. Also, if you have feedback for the code in general I would love to hear it! ---
**Author:** ![vulpesx](https://ziggit.dev/user_avatar/ziggit.dev/vulpesx/32/3989_2.png) [@vulpesx](https://ziggit.dev/u/vulpesx)\ **Post date:** [October 9, 2026, 6:58am UTC](https://ziggit.dev/t/error-when-using-discardremaining/17898/2 "2026-10-09T06:58:16Z")
`discardRemaining` will discard the remaining data **of the whole file** , the issue is that the implementation is doing an operation that is not valid for stdio–that being `stat` if your curious. Std returns `error.Unexpected` when the error is either, not supposed to be possible, or indicates a programmer bug like: doing operations on a file that doesn’t support it. Now it could still be a bug in std if its possible to avoid those operations or have a fallback, but I don’t know enough about windows to know this. * * * Explanation aside, `discardRemaining` is certainly not the behaviour you want in a REPL. The `take` family of functions return sub-slices of the interface buffer; `error.StreamTooLong` is returned when the buffer is not big enough. I am guessing you were trying to discard _the rest of the line_, in which case you’d use `discardDelimiterInclusive` If you want different behaviour explain what it is and we’d be glad to help. ---
**Author:** ![nrv30](https://ziggit.dev/user_avatar/ziggit.dev/nrv30/32/10025_2.png) [@nrv30](https://ziggit.dev/u/nrv30)\ **Post date:** [October 9, 2026, 6:25pm UTC](https://ziggit.dev/t/error-when-using-discardremaining/17898/3 "2026-10-09T18:25:24Z")
I changed to `discardDelimiterInclusive('\n')` and it’s working now. Thanks for the explanation 😊