c# 字符串操作总结

ToString 也可以自定义补零格式化：

(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

转换为二进制、八进制、十六进制输出：

int number = 15;
Convert.ToString(number, 2); // 结果：1111
Convert.ToString(number, 8); // 结果：17
Convert.ToString(number, 16); // 结果：f

自定义格式化器：

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;
  }
}

使用自定义格式化器：

String.Format(newCustomFormat(), "-> {0:Reverse} <-", "Hello World");
// 输出：-> dlroW olleH <-

字符串拼接

将数组中的字符串拼接成一个字符串：

var parts = new[] { "Foo", "Bar", "Fizz", "Buzz"};
var joined = string.Join(", ", parts);
// joined = "Foo, Bar, Fizz, Buzz"

以下四种方式都可以达到相同的字符串拼接的目的：

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}";

字符串内插法

简单用法：

var name = "World";
var str =$"Hello, {name}!";
// str = "Hello, World!"

带日期格式化：

var date = DateTime.Now;
var str = $"Today is {date:yyyy-MM-dd}！";

补齐格式化（Padding）：

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___."

结合内置快捷字母格式化：

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"

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