string pat = left + "(.*?)" + right; Regex regex = new Regex(pat, RegexOptions.None); Match match = regex.Match(str); Console.WriteLine("结果：" + match.Value.Trim());为什么输出的结果包含了left与right

如果输出的结果包含了 left 和 right，说明在正则表达式匹配时，left 和 right 都被包含在了匹配结果中。这是因为在正则表达式中，圆括号 () 是用来分组的符号，表示一组子表达式，而不是表示原始的字符。在这个正则表达式 `left + "(.*?)" + right` 中，圆括号将 `.*?` 匹配的子表达式包裹在了一起，表示这个子表达式是一个整体，要与字符串中的匹配部分一起输出。如果要去掉左右边界，可以使用非捕获分组 `(?:)`，如下所示：

string pat = left + "(.*?)" + right;
pat = "(?:" + left + ")" + "(.*?)" + "(?:" + right + ")";

这样就可以去掉左右边界的匹配结果了。

相关问题

var personName = !string.IsNullOrEmpty(input.PersonName?.Trim()); var ans = await _sysMainRep.AsQueryable().WhereIF(personName, u => SqlSugar.SqlFunc.Contains(u.CreateUserName, input.PersonName))改为用正则表达式进行模糊查询

可以使用正则表达式进行模糊查询，具体实现如下：

// 构造正则表达式
var regex = new Regex(input.PersonName?.Trim(), RegexOptions.IgnoreCase);

// 查询并筛选结果
var ans = await _sysMainRep.AsQueryable().Where(u => regex.IsMatch(u.CreateUserName)).ToListAsync();

这样就可以使用正则表达式进行模糊查询了。需要注意的是，在使用正则表达式进行模糊查询时，需要对用户输入的文本进行必要的转义，以避免正则表达式的特殊字符对查询造成影响。

vb.net Regex.IsMatch方法 九种重载的方法编程实例

以下是九种重载的实例：

1. 检查字符串是否与正则表达式匹配，返回布尔值。

Dim str As String = "Hello World"
Dim pattern As String = "Hello"
Dim isMatch As Boolean = Regex.IsMatch(str, pattern)
Console.WriteLine(isMatch)

2. 检查字符串是否与正则表达式匹配，返回布尔值，并设置匹配选项。

Dim str As String = "HELLO WORLD"
Dim pattern As String = "hello"
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim isMatch As Boolean = Regex.IsMatch(str, pattern, options)
Console.WriteLine(isMatch)

3. 检查字符串的某个子串是否与正则表达式匹配，返回布尔值。

Dim str As String = "This is a test"
Dim pattern As String = "test"
Dim startIndex As Integer = 10
Dim isMatch As Boolean = Regex.IsMatch(str, pattern, startIndex)
Console.WriteLine(isMatch)

4. 检查字符串的某个子串是否与正则表达式匹配，返回布尔值，并设置匹配选项。

Dim str As String = "This Is A Test"
Dim pattern As String = "test"
Dim startIndex As Integer = 10
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim isMatch As Boolean = Regex.IsMatch(str, pattern, options, startIndex)
Console.WriteLine(isMatch)

5. 检查字符串的某个子串是否与正则表达式匹配，返回布尔值，并设置匹配选项和超时时间。

Dim str As String = "This Is A Test"
Dim pattern As String = "test"
Dim startIndex As Integer = 10
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim timeout As TimeSpan = TimeSpan.FromSeconds(1)
Dim isMatch As Boolean = Regex.IsMatch(str, pattern, options, timeout, startIndex)
Console.WriteLine(isMatch)

6. 检查字符串的某个子串是否与正则表达式匹配，返回布尔值，并设置匹配选项、超时时间和输入字符串范围。

Dim str As String = "This Is A Test"
Dim pattern As String = "test"
Dim startIndex As Integer = 10
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim timeout As TimeSpan = TimeSpan.FromSeconds(1)
Dim inputLength As Integer = str.Length - startIndex
Dim isMatch As Boolean = Regex.IsMatch(str, pattern, options, timeout, inputLength, startIndex)
Console.WriteLine(isMatch)

7. 检查字符数组中的某个子串是否与正则表达式匹配，返回布尔值。

Dim chars() As Char = {"T"c, "h"c, "i"c, "s"c, " "c, "I"c, "s"c, " "c, "A"c, " "c, "T"c, "e"c, "s"c, "t"c}
Dim pattern As String = "test"
Dim isMatch As Boolean = Regex.IsMatch(chars, pattern)
Console.WriteLine(isMatch)

8. 检查字符数组中的某个子串是否与正则表达式匹配，返回布尔值，并设置匹配选项。

Dim chars() As Char = {"T"c, "H"c, "I"c, "S"c, " "c, "I"c, "S"c, " "c, "A"c, " "c, "T"c, "E"c, "S"c, "T"c}
Dim pattern As String = "test"
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim isMatch As Boolean = Regex.IsMatch(chars, pattern, options)
Console.WriteLine(isMatch)

9. 检查字符数组中的某个子串是否与正则表达式匹配，返回布尔值，并设置匹配选项、超时时间和输入字符数组范围。

Dim chars() As Char = {"T"c, "H"c, "I"c, "S"c, " "c, "I"c, "S"c, " "c, "A"c, " "c, "T"c, "E"c, "S"c, "T"c}
Dim pattern As String = "test"
Dim options As RegexOptions = RegexOptions.IgnoreCase
Dim timeout As TimeSpan = TimeSpan.FromSeconds(1)
Dim startIndex As Integer = 10
Dim length As Integer = chars.Length - startIndex
Dim isMatch As Boolean = Regex.IsMatch(chars, pattern, options, timeout, length, startIndex)
Console.WriteLine(isMatch)