如何在.NET中替换第一次出现的子字符串？

Question

我有字符串变量如下

string pctSign = "\0\0\0"; 

我想更换前两个字符“％”

i.e. Final o/p:- pctSign="%\0\0"; 

如何使用与string.replace做到这一点？

Answer 1

// Option 1 
var result = "%" + pctSign.Remove(0, 2); 

// Option 2 
var result = "%" + pctSign.Substring(2); 

// Option 3 
var regex = new Regex("^\\0"); 
var result = regex.Replace(pctSign, "%"); 

如果你绝对要用户String.Replace()，那么你可以编写自己的扩展方法：

public static class StringExtension 
{ 
    public static String Replace(this string self, 
             string oldString, string newString, 
             bool firstOccurrenceOnly = false) 
    { 
     if (!firstOccurrenceOnly) 
      return self.Replace(oldString, newString); 

     int pos = self.IndexOf(oldString); 
     if (pos < 0) 
      return self; 

     return self.Substring(0, pos) + newString 
       + self.Substring(pos + oldString.Length); 
    } 
} 

// Usage: 
var result = pctSign.Replace("/0", "%", true); 

Answer 2

string s = pctSign.Substring(2, pctSign.Length); 
s = "%" + s; 

Answer 3

试试这个：

var pctSign = "\0\0\0"; 
var result = string.Format("%{0}", pctSign.Substring(2)); 

Answer 4

你的意思是只有前两个那么

pctSign = "%"+pctSign.substring(2);