Zig调用print函数报错：expected error union type, found 'void'

初始代码 #

const bufPrint = @import("std").fmt.bufPrint;
const print = @import("std").debug.print;
const DefaultPrng = @import("std").rand.DefaultPrng;

fn qr(comptime a: []const u8) !void { print("\n{s}\n", .{a}); }

fn coati(comptime a: []const u8, b: i32) ![]const u8 {
    var buffer: [64]u8 = undefined;
    return try bufPrint(&buffer, "{d}: a {s} number.", .{b, a});
}

fn tapir(comptime a: []const u8) ![]const u8 {
    var buffer: [64]u8 = undefined;
    return try bufPrint(&buffer, "Checked by {s}.", .{a});
}

pub fn main() !void {
    const qa = @constCast(&DefaultPrng.init(0)).random().intRangeAtMost(i32, 0, 59);
    // const qb = qa / 20;

    try qr("Statements.");
    if (qa < 20) {
        const head = try coati("lesser", qa);
        const tail = try tapir("if-else statement");
        try print("{s} {s}\n", .{head, tail});
    } else if (qa < 40) {
        const head = try coati("middle", qa);
        const tail = try tapir("if-else statement");
        try print("{s} {s}\n", .{head, tail});
    } else {
        const head = try coati("greater", qa);
        const tail = try tapir("if-else statement");
        try print("{s} {s}\n", .{head, tail});
    }
}

编译错误信息 #

error: expected error union type, found 'void'
        try print("{s} {s}\n", .{head, tail});
            ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
referenced by:
    callMain: C:\ProgramData\chocolatey\lib\zig\tools\zig-windows-x86_64-0.12.0\lib\std\start.zig:511:32
    WinStartup: C:\ProgramData\chocolatey\lib\zig\tools\zig-windows-x86_64-0.12.0\lib\std\start.zig:350:45
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

修改后的代码（仍存在相同错误） #

const bufPrint = @import("std").fmt.bufPrint;
const print = @import("std").debug.print;
const DefaultPrng = @import("std").rand.DefaultPrng;

fn qr(comptime a: []const u8) !void { print("\n{s}\n", .{a}); }

fn coati(comptime a: []const u8, b: i32, c: []u8) ![]const u8 {
    return try bufPrint(c, "{d}: a {s} number.", .{b, a});
}

fn tapir(comptime a: []const u8, c: []u8) ![]const u8 {
    return try bufPrint(c, "Checked by {s}.", .{a});
}

pub fn main() !void {
    const qa = @constCast(&DefaultPrng.init(0))
        .random()
        .intRangeAtMost(i32, 0, 59);

    try qr("Statements.");
    if (qa < 20) {
        var kant: [64]u8 = undefined;
        const face = try coati("lesser", qa, &kant);
        const butt = try tapir("if-else statement", &kant);
        try print("{s} {s}\n", .{face, butt});
    } else if (qa < 40) {
        var kant: [64]u8 = undefined;
        const face = try coati("middle", qa, &kant);
        const butt = try tapir("if-else statement", &kant);
        try print("{s} {s}\n", .{face, butt});
    } else {
        var kant: [64]u8 = undefined;
        const face = try coati("greater", qa, &kant);
        const butt = try tapir("if-else statement", &kant);
        try print("{s} {s}\n", .{face, butt});
    }
}

问题分析与解决方法 #

核心错误原因 #

错误提示已明确指出：try关键字仅能用于调用返回错误联合类型的函数，但std.debug.print返回值为void——它不会抛出任何错误，因此不能在print前添加try。此前对coati/tapir字符串分配问题的推测是误判，实际问题出在print语句的try误用。

解决步骤 #

1. 移除print前的try：将所有try print(...)改为print(...)，直接调用即可。
2. 修复buffer复用问题：修改后的代码中，同一个kant buffer被coati和tapir先后使用，第二次bufPrint调用会覆盖第一次的内容，导致face指向的字符串被破坏。需为两个函数分配独立buffer，避免数据覆盖。

最终正确代码 #

const bufPrint = @import("std").fmt.bufPrint;
const print = @import("std").debug.print;
const DefaultPrng = @import("std").rand.DefaultPrng;

fn qr(comptime a: []const u8) void { print("\n{s}\n", .{a}); }

fn coati(comptime a: []const u8, b: i32, c: []u8) ![]const u8 {
    return try bufPrint(c, "{d}: a {s} number.", .{b, a});
}

fn tapir(comptime a: []const u8, c: []u8) ![]const u8 {
    return try bufPrint(c, "Checked by {s}.", .{a});
}

pub fn main() !void {
    const qa = @constCast(&DefaultPrng.init(0))
        .random()
        .intRangeAtMost(i32, 0, 59);

    qr("Statements.");
    if (qa < 20) {
        var coati_buf: [64]u8 = undefined;
        var tapir_buf: [64]u8 = undefined;
        const face = try coati("lesser", qa, &coati_buf);
        const butt = try tapir("if-else statement", &tapir_buf);
        print("{s} {s}\n", .{face, butt});
    } else if (qa < 40) {
        var coati_buf: [64]u8 = undefined;
        var tapir_buf: [64]u8 = undefined;
        const face = try coati("middle", qa, &coati_buf);
        const butt = try tapir("if-else statement", &tapir_buf);
        print("{s} {s}\n", .{face, butt});
    } else {
        var coati_buf: [64]u8 = undefined;
        var tapir_buf: [64]u8 = undefined;
        const face = try coati("greater", qa, &coati_buf);
        const butt = try tapir("if-else statement", &tapir_buf);
        print("{s} {s}\n", .{face, butt});
    }
}

额外优化：qr函数内的print同样无需try，因此可将qr的返回类型从!void改为void，去掉不必要的错误处理。

内容的提问来源于stack exchange，提问作者Prido1024