# 字符串

> string 类型是一种特殊的引用类型，每次操作都会生成一个新的副本进行操作。

## 属性

**Length**

获取当前字符串中字符的个数

```csharp
string str = "hello world";
int len = str.Length; 
```

## 方法

**Compare**

静态方法，比较两个字符串的先后，返回值小于零，说明字符串A顺序在字符串B前面；返回零，说明两者顺序相同；大于零，说明字符串A顺序在字符串B后面

常用重载

- Compare(String? strA, String? strB)

- Compare(String? strA, String? strB, bool ignoreCase) //是否忽略大小写
- Compare(String? strA, String? strB, bool ignoreCase, CultureInfo? culture) //指定区域信息

```csharp
string strA = "001";
string strB = "002";
int result = String.Compare(strA, strB);
```

**Concat**

静态方法，连接指定的字符串，并返回拼接后的字符串

常用重载

- Concat(params String?[] values)
- Concat(String? str0, String? str1)

```csharp
string[] strs = new string[]{"a","b","c","d"};
string strNew = String.Concat(strs);
```

**Copy**

静态方法，复制指定的字符串

```csharp
String.Copy("abcde")
```

**Equals**

静态方法，判断两个字符串是否相等

常用重载

- Equals(String? a, String? b)
- Equals(String? a, String? b, StringComparison comparisonType)用于指定比较用的排序规则和是否区分大小写

```csharp
string str1 = "hello world";
string str2 = "Hello World";
if(string.Equals(str1, str2)
{
    ……
}
```

**Join**

静态方法，用指定的字符或字符串，连接多个字符串

常用重载

- Join(String? separator, IEnumerable<String?> values)
- Join(String? separator, params String?[] value)
- Join(char separator, params String?[] value)

```csharp
string[] strs = new string[] { "a", "b", "c", "d" };
string strNew = string.Join(',',strs);
```

**CompareTo**

用于和指定的字符串做比较

```csharp
string str1 = "Hello";
string str2 = "hello";
int result = str1.CompareTo(str2);
```

**Contains**

判断字符串是否包含指定字符或字符串

常用重载

- Contains(String value)
- Contains(char value)

```csharp
string str = "hello world";
bool result = str.Contains('o');
```

**EndsWith**

判断字符串是否以指定的字符或字符串结尾

常用重载

- EndsWith(char value)
- EndsWith(String value)
- EndsWith(String value, bool ignoreCase, CultureInfo? culture)
- EndsWith(String value, StringComparison comparisonType)

```csharp
string str = "hello world";
bool result = str.EndWith('o');
```

**Equals**

判断字符串是否与指定的字符串相等

常用重载

- Equals(String? value)
- Equals(String? value, StringComparison comparisonType)

```csharp
string str = "hello world";
bool result = str.Equals("HELLO WORLD");
```

**IndexOf**

获取指定字符或字符串在字符串中首次出现的位置

常用重载

- IndexOf(String value, StringComparison comparisonType)
- IndexOf(String value, int startIndex, StringComparison comparisonType)
- IndexOf(String value, int startIndex, int count, StringComparison comparisonType)
- IndexOf(String value, int startIndex, int count)
- IndexOf(String value, int startIndex)
- IndexOf(String value)
- IndexOf(char value, StringComparison comparisonType)
- IndexOf(char value, int startIndex, int count)
- IndexOf(char value, int startIndex)
- IndexOf(char value)

```csharp
string str = "hello world";
int result = str.Indexof('o');
```

**LastIndexOf**

获取指定字符或字符串在字符串中最后一次出现的位置

常用重载

- LastIndexOf(char value, int startIndex, int count)
- LastIndexOf(char value, int startIndex)
- LastIndexOf(String value, StringComparison comparisonType)
- LastIndexOf(String value, int startIndex, StringComparison comparisonType)
- LastIndexOf(char value)
- LastIndexOf(String value, int startIndex, int count)
- LastIndexOf(String value, int startIndex)
- LastIndexOf(String value)
- LastIndexOf(String value, int startIndex, int count, StringComparison comparisonType)
- LastIndexOfAny(char[] anyOf)
- LastIndexOfAny(char[] anyOf, int startIndex)
- LastIndexOfAny(char[] anyOf, int startIndex, int count)

```csharp
string str = "hello world";
int result = str.LastIndexOf('o');
```

**PadLeft**

把字符串从左侧填充到指定的长度

常用重载

- PadLeft(int totalWidth)  用空格填充
- PadLeft(int totalWidth, char paddingChar) 用指定字符串填充

```csharp
string str = "hello";
string str1 = str.PadLeft(10);
```

**PadRight**

把字符串从右侧填充到指定的长度

常用重载

- PadRight(int totalWidth)  用空格填充
- PadRight(int totalWidth, char paddingChar) 用指定字符串填充

```csharp
string str = "hello";
string str1 = str.PadRight(10);
```

**Remove**

在字符串中从指定位置移除指定长度的字符串

常用重载

- Remove(int startIndex) 指定位置后面的字符串全部移除
- Remove(int startIndex, int count)

```csharp
string str = "hello";
string str1 = str.Remove(2,1);
```

**Replace**

用指定的新字符串替换指定的老字符串

常用重载

- Replace(char oldChar, char newChar)
- Replace(String oldValue, String? newValue)
- Replace(String oldValue, String? newValue, bool ignoreCase, CultureInfo? culture)
- Replace(String oldValue, String? newValue, StringComparison comparisonType)

```csharp
string str1 = "Hello World";
string str2 = str1.Replace("World","China");
```

**Split**

按照指定的字符将字符串拆分为数组

常用重载

- Split(String[]? separator, int count, StringSplitOptions options)
- Split(String? separator, int count, StringSplitOptions options = StringSplitOptions.None)
- Split(String[]? separator, StringSplitOptions options)
- Split(char[]? separator, int count, StringSplitOptions options)
- Split(String? separator, StringSplitOptions options = StringSplitOptions.None)
- Split(char[]? separator, StringSplitOptions options)
- Split(char separator, StringSplitOptions options = StringSplitOptions.None)
- Split(params char[]? separator)
- Split(char[]? separator, int count)、
- Split(char separator, int count, StringSplitOptions options = StringSplitOptions.None)

```csharp
string str = "Hello World";
string[] strs = str.Split('');
```

**StartsWith**

判断字符串是否已指定的字符或字符串开头

常用重载

- StartsWith(char value)
- StartsWith(String value)
- StartsWith(String value, bool ignoreCase, CultureInfo? culture)
- StartsWith(String value, StringComparison comparisonType)

```csharp
string str = "Hello World";
bool result = str.StartsWith('h');
```

**Substring**

从制定位置截取指定长度的字符串

常用重载

- Substring(int startIndex)
- Substring(int startIndex, int length)

```csharp
string str = "Hello World";
string result = str.Substring(2,2);
```

**ToLower**

将字符串转换成小写形式

常用重载

- ToLower()
- ToLower(CultureInfo? culture)，用于指定区域性信息

```csharp
string str = "HELLO WORLD";
string strNew = str.ToLower();
```

**ToUpper**

将字符串转化成大写形式

常用重载

- ToUpper()
- ToUpper(CultureInfo? culture)，用于指定区域性信息

```csharp
string str = "hello world";
string strNew = str.ToUpper();
```

**Trim**

去掉字符串两端指定的字符

常用重载

- Trim()
- Trim(char trimChar)
- Trim(params char[]? trimChars)

```csharp
string str = "  hello world  ";
string strNew = str.Trim();
```

**TrimEnd**

去掉字符串右端指定的字符

常用重载

- TrimEnd()
- TrimEnd(char trimChar)
- TrimEnd(params char[]? trimChars)

```csharp
string str = "  hello world  ";
string strNew = str.TrimEnd();
```

**TrimStart**

去掉字符串左端指定的字符

常用重载

- TrimStart()
- TrimStart(char trimChar)
- TrimStart(params char[]? trimChars)

```csharp
string str = "  hello world  ";
string strNew = str.TrimStart();
```