open/read file

[royal topaz]

Hi, how can i open and read a file and throw an error if it doesn't exist ?? I can't find anything on the internet

[flat moat]

https://ziglang.org/documentation/master/std/#A;std:fs.Dir.openFile

[gaunt remnant]

here's some code that's should make it work.

    const file = std.fs.cwd().openFile("your_file", .{}) catch |err| {
        switch(err) {
            .FileNotFound => {},
            else => {},
        }
    };

    const content = try file.readToEndAlloc(alloc, max_bytes);

However keep in mind that cwd() uses the current working directory and many things are context dependened.

(i would also strongly recommend trying to figure it out yourself, before just blindly copy + pasting this)

[flat moat]

theres like 7 different file opening functions but they all do basically the same thing, really only different how theyre called

[royal topaz]

thanks , what i am supposed to put in the flags parameter ?

[gaunt remnant]

zig's std code is very readable, why not try and read it? :)

(in the docs, you can click on the flags type, and there you get further information on that type)

[royal topaz]

i tried and found that : pub const OpenMode = enum { read_only, write_only, read_write, }; but it doesn't work

[gaunt remnant]

https://ziglang.org/documentation/master/std/#A;std:fs.File.OpenFlags

[royal topaz]

why can't this work with the args ?

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();

    const allocator = gpa.allocator();

    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);

    var argc = args.len;
    if (argc < 2) {
        std.log.err("Usage: {} script file\n", args[0]);
        return;
    }

    var file = try std.fs.cwd().openFile(args[0], .{});
    defer file.close();```

I think i need to cast the arg to a const u8 ?

[flat moat]

std.log.err("Usage: {} script file\n", args[0]); has to be
std.log.err("Usage: {s} script file\n", .{args[0]});

[royal topaz]

thank you

it's annoying that errors don't refer to my code

[flat moat]

yeah it does that sometimes, I imagine it's something that can/will be changed

[gaunt remnant]

Yup I'd also believe that.

[primal bobcat]

You can compile with -freference-trace to see the full trace.

[royal topaz]

I can't get this to work why ? I tried a lot of things

var file = std.fs.cwd().openFile(args[0], .{}) catch |err| {
        switch (err) {
            .FileNotFound => {
                return;
            },
            else => {},
        }
    };
    defer file.close();```

```zig build-exe MyRadarZig Debug native 1 errors
src/main.zig:31:14: error: expected type 'error{AccessDenied,BadPathName,DeviceBusy,FileBusy,FileLocksNotSupported,FileNotFound,FileTooBig,InvalidHandle,InvalidUtf8,IsDir,NameTooLong,NoDevice,NoSpaceLeft,NotDir,PathAlreadyExists,PipeBusy,ProcessFdQuotaExceeded,SharingViolation,SymLinkLoop,SystemFdQuotaExceeded,SystemResources,Unexpected,WouldBlock}', found '@TypeOf(.enum_literal)'
.FileNotFound => {
~^~~~~~~~~~~~```

[flat moat]

you have to do error.FileNotFound in the switch

[royal topaz]

var file = std.fs.cwd().openFile(args[0], .{}) catch |err| {
        switch (err) {
            error.FileNotFound => {
                return;
            },
            else => {},
        }
    };
    defer file.close();```

Still doesn't work

[flat moat]

else => {} is of type void

youre basically telling the compiler to make file into nothing if any other error happens

[royal topaz]

ah fuck me

thanks