[C#.NET 拾遗补漏]01：字符串操作

西安女子 發表於 2020-6-3 10:06:00

<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">字符串操作在任意编程语言的日常编程中都随处可见，今天来汇总一下 C# 中关于字符串的一些你可能遗忘或遗漏的知识点。
<h2 style="box-sizing: border-box; margin-top: 25px; margin-bottom: 20px; font-weight: bold; font-size: 20px; color: rgba(34, 34, 34, 1); padding-bottom: 3px; border-bottom: 2px solid rgba(255, 190, 0, 1); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; text-align: start; white-space: normal">逐字字符串</h2>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">在普通字符串中，反斜杠字符是转义字符。而在逐字字符串（Verbatim Strings）中，字符将被编程器按照原义进行解释。使用逐字字符串只需在字符串前面加上 @ 符号。
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">// 逐字字符串：转义符 var filename = @"c:\temp\newfile.txt"; Console.WriteLine(filenaame); // 逐字字符串：多行文本 var multiLine = @"This is a multiline paragraph."; Console.WriteLine(multiLine); // 非逐字字符串 var escapedFilename = "c:\temp\newfile.txt"; Console.WriteLine(escapedFilename);</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">输出：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">c:\temp\newfile.txt This is a multiline paragraph. c: emp ewfile.txt</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">逐字字符串中唯一不被原样解释的字符是双引号。由于双引号是定义字符串的关键字符，所以在逐字字符串中要表达双引号需要用双引号进行转义。
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">varstr = @"""I don't think so"", he said."; Console.WriteLine(str); // 输出："I don't think so", he said.</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">在逐字字符串中也可以 $ 符号实现字符串内插值。
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">Console.WriteLine($@"Testing \n 1 2 {5 - 2}"); // 输出：Testing \n 1 2 3</code></pre>
<h2 style="box-sizing: border-box; margin-top: 25px; margin-bottom: 20px; font-weight: bold; font-size: 20px; color: rgba(34, 34, 34, 1); padding-bottom: 3px; border-bottom: 2px solid rgba(255, 190, 0, 1); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; text-align: start; white-space: normal">数字格式化转换</h2>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">典型的的格式化方法为：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">string.Format("{index[:format]}", number)</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">可使用“0”和“#”占位符进行补位。“0” 表示位数不够位数就补充“0”，小数部分如果位数多了则会四舍五入；“#”表示占位，用于辅助“0”进行补位。
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">标准格式化用法：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">// “0”描述：占位符，如果可能，填充位 string.Format("{0:000000}",1234); // 结果：001234 // “#”描述：占位符，如果可能，填充位 string.Format("{0:######}",1234);// 结果：1234 string.Format("{0:#0####}",1234);// 结果：01234 string.Format("{0:0#0####}",1234); // 结果：0001234 // "."描述：小数点 string.Format("{0:000.000}", 1234); // 结果：1234.000 string.Format("{0:000.000}", 4321.12543); // 结果：4321.125 // ","描述：千分表示 string.Format("{0:0,0}", 1234567); //结果：1,234,567 // "%"描述：格式化为百分数 string.Format("{0:0%}",1234); // 结果：123400% string.Format("{0:#%}", 1234.125); // 结果：123413% string.Format("{0:0.00%}",1234); // 结果：123400.00% string.Format("{0:#.00%}",1234.125); // 结果：123412.50%</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">内置快捷字母格式化用法：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">// E-科学计数法表示 (25000).ToString("E"); // 结果：2.500000E+004 // C-货币表示，带有逗号分隔符，默认小数点后保留两位，四舍五入 (2.5).ToString("C"); // 结果：￥2.50 // D-十进制数 (25).ToString("D5"); // 结果：00025 // F-浮点数，保留小数位数(四舍五入) (25).ToString("F2"); // 结果：25.00 // G-常规，保留指定位数的有效数字，四舍五入 (2.52).ToString("G2"); // 结果：2.5 // N-带有逗号分隔符，默认小数点后保留两位，四舍五入 (2500000).ToString("N"); // 结果：2,500,000.00 // X-十六进制，非整型将产生格式异常 (255).ToString("X"); // 结果：FF</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal"><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; font-size: 13px; line-height: 1; vertical-align: middle; padding: 0.1em 0.3em; border-radius: 3px; background: rgba(255, 246, 234, 1); overflow-wrap: break-word; -webkit-box-decoration-break: clone">ToString</code> 也可以自定义补零格式化：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">(15).ToString("000"); // 结果：015 (15).ToString("value is 0"); // 结果：value is 15 (10.456).ToString("0.00"); // 结果：10.46 (10.456).ToString("00"); // 结果：10 (10.456).ToString("value is 0.0"); // 结果：value is 10.5</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">转换为二进制、八进制、十六进制输出：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">int number = 15; Convert.ToString(number, 2);// 结果：1111 Convert.ToString(number, 8);// 结果：17 Convert.ToString(number, 16); // 结果：f</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">自定义格式化器：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">public class CustomFormat : IFormatProvider, ICustomFormatter { public string Format(string format, object arg, IFormatProvider formatProvider) { if (!this.Equals(formatProvider)) { return null; } if (format == "Reverse") { return string.Join("", arg.ToString().Reverse()); } return arg.ToString(); } public object GetFormat(Type formatType) { return formatType == typeof(ICustomFormatter) ? this : null; } }</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">使用自定义格式化器：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">String.Format(newCustomFormat(), "-> {0:Reverse} <-", "Hello World"); // 输出：-> dlroW olleH <-</code></pre>
<h2 style="box-sizing: border-box; margin-top: 25px; margin-bottom: 20px; font-weight: bold; font-size: 20px; color: rgba(34, 34, 34, 1); padding-bottom: 3px; border-bottom: 2px solid rgba(255, 190, 0, 1); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; text-align: start; white-space: normal">字符串拼接</h2>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">将数组中的字符串拼接成一个字符串：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">var parts = new[] { "Foo", "Bar", "Fizz", "Buzz"}; var joined = string.Join(", ", parts); // joined = "Foo, Bar, Fizz, Buzz"</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">以下四种方式都可以达到相同的字符串拼接的目的：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">string first = "Hello"; string second = "World"; string foo = first + " " + second; string foo = string.Concat(first, " ", second); string foo = string.Format("{0} {1}", firstname, lastname); string foo = $"{firstname} {lastname}";</code></pre>
<h2 style="box-sizing: border-box; margin-top: 25px; margin-bottom: 20px; font-weight: bold; font-size: 20px; color: rgba(34, 34, 34, 1); padding-bottom: 3px; border-bottom: 2px solid rgba(255, 190, 0, 1); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; text-align: start; white-space: normal">字符串内插法</h2>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">简单用法：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">var name = "World"; var str =$"Hello, {name}!"; // str = "Hello, World!"</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">带日期格式化：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">var date = DateTime.Now; var str = $"Today is {date:yyyy-MM-dd}！";</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">补齐格式化（Padding）：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">var number = 42; // 向左补齐 var str = $"The answer to life, the universe and everything is {number, 5}."; // str = "The answer to life, the universe and everything is ___42." ('_'表示空格) // 向右补齐 var str = $"The answer to life, the universe and everything is ${number, -5}."; // str = "The answer to life, the universe and everything is 42___."</code></pre>
<p style="box-sizing: border-box; font-size: 15px; line-height: 1.8; margin-right: 1px; margin-bottom: 20px; margin-left: 1px; letter-spacing: 0.5px; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; white-space: normal">结合内置快捷字母格式化：
<pre><code style="box-sizing: border-box; font-family: SFMono-Regular, Menlo, Monaco, Consolas, monospace; letter-spacing: 0; line-height: 1.45; vertical-align: middle; padding: 15px; border-radius: 5px; background: rgba(40, 44, 52, 1); overflow-wrap: unset; -webkit-box-decoration-break: clone; overflow-x: auto; border-style: none; color: rgba(171, 178, 191, 1)">var amount = 2.5; var str = $"It costs {amount:C}"; // str = "￥2.50" var number = 42; var str = $"The answer to life, the universe and everything is {number, 5:f1}."; // str = "The answer to life, the universe and everything is ___42.1"</code></pre>
<blockquote style="box-sizing: border-box; margin: 0 6px 20px; background-color: rgba(248, 248, 248, 1); padding: 15px; border-left: none; border-radius: 4px; quotes: none; color: rgba(85, 85, 85, 1); font-size: 14px; line-height: 1.7; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif; text-align: start; white-space: normal">
参考：
1.《C# 7.0 in a Nutshell》
2. https://bit.ly/2U1eIK9
</blockquote>

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作者：精致码农-王亮

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来源：https://www.cnblogs.com/willick/p/13035697.html

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[C#.NET 拾遗补漏]01：字符串操作