rust - 如何将格式化字符串写入文件？

Question

我想将函数的输出写入文件。我预计 write_fmt是我需要的:

use std::{
    fs::File,
    io::{BufWriter, Write},
};

fn main() {
    let write_file = File::create("/tmp/output").unwrap();
    let mut writer = BufWriter::new(&write_file);

    // From my function
    let num = 1;
    let factorial = 1;

    writer.write_fmt("Factorial of {} = {}", num, factorial);
}

错误

error[E0061]: this function takes 1 parameter but 3 parameters were supplied
  --> src/main.rs:11:12
   |
11 |     writer.write_fmt("Factorial of {} = {}", num, factorial);
   |            ^^^^^^^^^ expected 1 parameter

这似乎是错误的，文档中没有太多可用的内容。

Answer 1

documentation指示问题:write_fmt方法接受一个参数，类型为 std::fmt::Arguments , 可以通过 format_args! 构建宏。它还建议了最佳使用方法:

The write! macro should be favored to invoke this method instead.

一个电话 write! (或 writeln! )就像 println! ，但通过将要写入的位置作为第一个参数传递:

write!(&mut writer, "Factorial of {} = {}", num, factorial);

(请注意，文档在每一页的顶部都有一个搜索栏，因此您可以通过在此处搜索 <name>! 来找到有关宏的文档。)