替换C#中字符串的首次出现 [英] Replace first occurence of a string in c#

问题描述

以下是用于替换文件中字符串首次出现的代码.

The following is the code for replacing fist occurrence of a string in a file.

public static string ReplaceFirstOccurrance(string original, string oldValue, string newValue)
{
    if (String.IsNullOrEmpty(original))
        return String.Empty;
    if (String.IsNullOrEmpty(oldValue))
        return original;
    if (String.IsNullOrEmpty(newValue))
        newValue = String.Empty;
    int loc = original.IndexOf(oldValue);
    if(loc==-1)
       return original;
    return original.Remove(loc, oldValue.Length).Insert(loc, newValue);
}

如果我要替换的字符串是文件的最后一行，那么它就不会被替换.知道为什么会发生这种情况吗?

这是我从中调用该函数的代码

If the string that I want to replace is the last line of the file then it is not getting replaced.Any idea why this is happening?

This is the code from where I am calling the function

 private void Transform_Click(object sender, EventArgs e)
        {
                      FileStream fread = new FileStream(despath, FileMode.Open);
                            StreamReader sfread = new StreamReader(fread);
                            string txt = sfread.ReadToEnd();
                            fread.Close();
                            
                            string actual ="This is actual Sample";
                       
                            string replace = "This is replaced line"+count;
                       
                            string replaceVariable = ReplaceFirstOccurrance(txt, actual, replace);
                         
                            FileStream filewrite = new FileStream(despath, FileMode.Create);
                            StreamWriter filew = new StreamWriter(filewrite);

                            filew.Write(replaceVariable);

                            filew.Close();
                            filewrite.Close();
                            count++;
}

如果这是实际示例"是文件中的最后一行，则不会替换它.

If "This is actual sample" is the last line in the file,it is not getting replaced.

推荐答案

，因为它删除了位置，所以insert()找不到任何内容loc
尝试为您的行返回"original.Remove(loc，oldValue.Length).Insert(loc，newValue);"

because it deletes the position, insert() doesnt find any loc
try this instead for your line return "original.Remove(loc, oldValue.Length).Insert(loc, newValue);"

string temp = orignal.Substring(0, orignal.IndexOf(oldv));
string temp2 = orignal.Substring(orignal.IndexOf(oldv) + oldv.Length);
return temp + newv + temp2;

使用string.Replace()有什么问题?

And what is wrong with using string.Replace()?

if (original==null) return string.Empty
else return original.Replace(oldValue, newValue);

另外，您不是逐行读取文件，而是一次将整个文件读入一个字符串中.如果您在2个或更多位置有这是实际示例"，则仅第一个将被替换.

逐行读取和替换:

Also, you are not reading file line by line, you read it whole at once into one string. If you have "This is actual sample" in 2 or more places, only first will be replaced.

Reading and replaceing line by line:

private void Transform_Click(object sender, EventArgs e)
{
    FileStream fread = new FileStream(despath, FileMode.Open);
    StreamReader sfread = new StreamReader(fread);
    FileStream filewrite = new FileStream(despath, FileMode.Create);
    StreamWriter filew = new StreamWriter(filewrite);

    while (!sfread.EndOfStream)
    {
        string line = sfread.ReadLine();
        
        string replaceVariable = ReplaceFirstOccurrance(line, 
            "This is actual Sample", 
            "This is replaced line"+count.ToString());
                    
        filew.Write(replaceVariable);
count++;
    }    
    filew.Close();
    filewrite.Close();
    
fread.Close();
}

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