Parse an integer from zero terminated string

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1

Hi all, I want learn my first bits of zig by writing some simple programs that read the command line arguments and I can’t figure out how to read some ints.

Following this post Read command line arguments I tried using std.os.argv which seems the less verbose one and:

    const n: i32 = try std.fmt.parseInt(i32, std.os.argv[1], 10);

But parseInt is expecting a []const u8 and std.os.arvg.[1] has type [*:0]u8 so I get an error. Is there a way to parse some value of the latter type directly? Or do I have to instantiate an array? How is that done? Or there is another way suggested for doing this?

2

You can use the std.mem.sliceTo function to convert an argv value.

For instance,

const std = @import("std");

pub fn main() !void {
    const data = std.os.argv[1];
    std.debug.print("{}\n", .{try std.fmt.parseInt(i32, std.mem.sliceTo(data, 0), 0)}); // 4
}

see also: API reference page

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3

There’s also std.mem.span which is like a specialized version of sliceTo. So the call would be std.mem.span(std.os.argv[1]). I hadn’t run into this situation with args since I’m used to using std.process.args which returns an iterator over the args as strings:

var args_iter = std.process.args();
_ = args_iter.next(); // skip program name
const second_arg = args_iter.next() orelse print_usage_and_exit();
const n: i32 = try std.fmt.parseInt(i32, second_arg, 10);
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4

FYI:

std.os.argv is not supported on Windos OS.
In Windows, It must use std.process.args function.

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5

You mean argsWithAllocator or argsAlloc. Windows and WASI need an allocator.

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