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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../about.html">Rusty Book</a></li><li class="chapter-item expanded affix "><li class="part-title">Awesome</li><li class="spacer"></li><li class="chapter-item expanded "><a href="../awesome-daily-dev.html">日常开发常用库</a></li><li class="chapter-item expanded "><a href="../awesome-superstar.html">Rust 明星项目</a></li><li class="chapter-item expanded "><a href="../awesome-empowering-js.html">使用 Rust 增强 JS</a></li><li class="chapter-item expanded "><a href="../awesome-games.html">Rust开发的游戏</a></li><li class="chapter-item expanded "><a href="../awesome-gamedev.html">游戏引擎</a></li><li class="chapter-item expanded affix "><li class="part-title">Awesome + Cookbook</li><li class="spacer"></li><li class="chapter-item expanded "><a href="../algos/awesome.html">实用算法</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><div>数据结构</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../algos/datastructures/bitfield.html">位字段</a></li></ol></li><li class="chapter-item "><a href="../algos/randomness.html">生成随机值</a></li><li class="chapter-item "><a href="../algos/sorting.html">Vec 排序</a></li><li class="chapter-item "><div>压缩算法</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../algos/compression/tar.html">使用.tar包</a></li></ol></li><li class="chapter-item "><div>密码学</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../algos/cryptography/hashing.html">哈希</a></li><li class="chapter-item "><a href="../algos/cryptography/encryption.html">加密</a></li></ol></li><li class="chapter-item "><div>数学计算</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../algos/math/linear-algebra.html">线性代数</a></li><li class="chapter-item "><a href="../algos/math/trigonometry.html">三角函数</a></li><li 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<main>
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<h1 id="文件读写"><a class="header" href="#文件读写">文件读写</a></h1>
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<h2 id="迭代文件中的内容行"><a class="header" href="#迭代文件中的内容行">迭代文件中的内容行</a></h2>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use std::fs::File;
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use std::io::{Write, BufReader, BufRead, Error};
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fn main() -> Result<(), Error> {
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let path = "lines.txt";
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// 创建文件
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let mut output = File::create(path)?;
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// 写入三行内容
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write!(output, "Rust\n💖\nFun")?;
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let input = File::open(path)?;
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let buffered = BufReader::new(input);
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// 迭代文件中的每一行内容，line 是字符串
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for line in buffered.lines() {
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println!("{}", line?);
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}
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Ok(())
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}</code></pre></pre>
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<h2 id="避免对同一个文件进行读写"><a class="header" href="#避免对同一个文件进行读写">避免对同一个文件进行读写</a></h2>
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<p><a href="https://docs.rs/same-file/latest/same_file/">same_file</a> 可以帮我们识别两个文件是否是相同的。</p>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use same_file::Handle;
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use std::fs::File;
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use std::io::{BufRead, BufReader, Error, ErrorKind};
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use std::path::Path;
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fn main() -> Result<(), Error> {
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let path_to_read = Path::new("new.txt");
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// 从标准输出上获取待写入的文件名
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let stdout_handle = Handle::stdout()?;
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// 将待写入的文件名跟待读取的文件名进行比较
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let handle = Handle::from_path(path_to_read)?;
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if stdout_handle == handle {
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return Err(Error::new(
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ErrorKind::Other,
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"You are reading and writing to the same file",
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));
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} else {
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let file = File::open(&path_to_read)?;
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let file = BufReader::new(file);
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for (num, line) in file.lines().enumerate() {
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println!("{} : {}", num, line?.to_uppercase());
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}
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}
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Ok(())
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}</code></pre></pre>
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<p>以下代码会报错，因为待写入的文件名也是 <em>new.txt</em>，跟待读取的文件名相同</p>
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<pre><code class="language-shell">cargo run >> ./new.txt
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</code></pre>
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<h3 id="使用内存映射访问文件"><a class="header" href="#使用内存映射访问文件">使用内存映射访问文件</a></h3>
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<p><a href="https://docs.rs/memmap/">memmap</a> 能创建一个文件的内存映射( memory map )，然后模拟一些非顺序读。</p>
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<p>使用内存映射，意味着你将相关的索引加载到内存中，而不是通过 <a href="https://doc.rust-lang.org/std/fs/struct.File.html#method.seek">seek</a> 的方式去访问文件。</p>
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<p><a href="https://docs.rs/memmap/*/memmap/struct.Mmap.html#method.map">Mmap::map</a> 函数会假定待映射的文件不会同时被其它进程修改。</p>
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<pre><pre class="playground"><code class="language-rust editable edition2021">use memmap::Mmap;
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use std::fs::File;
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use std::io::{Write, Error};
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fn main() -> Result<(), Error> {
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write!(File::create("content.txt")?, "My hovercraft is full of eels!")?;
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let file = File::open("content.txt")?;
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let map = unsafe { Mmap::map(&file)? };
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let random_indexes = [0, 1, 2, 19, 22, 10, 11, 29];
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assert_eq!(&map[3..13], b"hovercraft");
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let random_bytes: Vec<u8> = random_indexes.iter()
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.map(|&idx| map[idx])
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.collect();
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assert_eq!(&random_bytes[..], b"My loaf!");
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Ok(())
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}</code></pre></pre>
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