如何在 String.replace 中忽略大小写

Question

string sentence = "We know it contains 'camel' word.";
// Camel can be in different cases:
string s1 = "CAMEL";
string s2 = "CaMEL";
string s3 = "CAMeL";
// ...
string s4 = "Camel";
// ...
string s5 = "camel";

尽管 string.Replace 不支持左侧字符串的 ignoreCase ，如何将句子中的“camel”替换为“horse”？

Answer 1

使用正则表达式：

var regex = new Regex( "camel", RegexOptions.IgnoreCase );
var newSentence = regex.Replace( sentence, "horse" );

当然，这也会匹配包含camel的单词，但不清楚您是否想要这样。

如果您需要精确匹配，您可以使用自定义 MatchEvaluator。

public static class Evaluators
{
    public static string Wrap( Match m, string original, string format )
    {
        // doesn't match the entire string, otherwise it is a match
        if (m.Length != original.Length)
        {
            // has a preceding letter or digit (i.e., not a real match).
            if (m.Index != 0 && char.IsLetterOrDigit( original[m.Index - 1] ))
            {
                return m.Value;
            }
            // has a trailing letter or digit (i.e., not a real match).
            if (m.Index + m.Length != original.Length && char.IsLetterOrDigit( original[m.Index + m.Length] ))
            {
                return m.Value;
            }
        }
        // it is a match, apply the format
        return string.Format( format, m.Value );
    }
} 

与前面的示例一起使用，将匹配项包装在跨度中，如下所示：

var regex = new Regex( highlightedWord, RegexOptions.IgnoreCase );
foreach (var sentence in sentences)
{
    var evaluator = new MatchEvaluator( match => Evaluators.Wrap( match, sentence, "<span class='red'>{0}</span>" ) );
    Console.WriteLine( regex.Replace( sentence, evaluator ) );
}

Answer 2

为字符串添加一个扩展方法来实现这个目的：

用法：

string yourString = "TEXTTOREPLACE";
yourString.Replace("texttoreplace", "Look, I Got Replaced!", StringComparison.OrdinalIgnoreCase);

代码：

using System;
using System.Collections.Generic;
using System.IO;

public static class Extensions
{       
    public static string Replace(this string source, string oldString, string newString, StringComparison comp)
    {
        int index = source.IndexOf(oldString, comp);

        // Determine if we found a match
        bool MatchFound = index >= 0;

        if (MatchFound)
        {
            // Remove the old text
            source = source.Remove(index, oldString.Length);

            // Add the replacemenet text
            source = source.Insert(index, newString);
        }

        // recurse for multiple instances of the name
        if (source.IndexOf(oldString, comp) != -1)
        {
            source = Replace(source, oldString, newString, comp);
        }

        return source;
    }
}

Answer 3

这是一个采用 StringComparison 的扩展方法，使用 string.IndexOf:

    [Pure]
    public static string Replace(this string source, string oldValue, string newValue, StringComparison comparisonType)
    {
        if (source.Length == 0 || oldValue.Length == 0)
            return source;

        var result = new System.Text.StringBuilder();
        int startingPos = 0;
        int nextMatch;
        while ((nextMatch = source.IndexOf(oldValue, startingPos, comparisonType)) > -1)
        {
            result.Append(source, startingPos, nextMatch - startingPos);
            result.Append(newValue);
            startingPos = nextMatch + oldValue.Length;
        }
        result.Append(source, startingPos, source.Length - startingPos);

        return result.ToString();
    }

顺便说一句，这里还有一个类似的 Contains 方法也采用 StringComparison:

    [Pure]
    public static bool Contains(this string source, string value, StringComparison comparisonType)
    {
        return source.IndexOf(value, comparisonType) >= 0;
    }

一些测试：

[TestFixture]
public class ExternalTests
{
    private static string[] TestReplace_args =
        {
            "ab/B/c/ac",
            "HELLO World/Hello/Goodbye/Goodbye World",
            "Hello World/world/there!/Hello there!",
            "hello WoRlD/world/there!/hello there!",
            "///",
            "ab///ab",
            "/ab/cd/",
            "a|b|c|d|e|f/|//abcdef",
            "a|b|c|d|e|f|/|/:/a:b:c:d:e:f:",
        };

    [Test, TestCaseSource("TestReplace_args")]
    public void TestReplace(string teststring)
    {
        var split = teststring.Split("/");
        var source = split[0];
        var oldValue = split[1];
        var newValue = split[2];
        var result = split[3];
        Assert.That(source.Replace(oldValue, newValue, StringComparison.OrdinalIgnoreCase), Is.EqualTo(result));
    }
}

Answer 4

这是我的扩展方法，它将 Tom Beech 的 与 Tom Beech 的递归性相结合。 com/a/19734023/403404">sntbob，以及对 ksun 指出的错误的更清晰的修复。

代码：

public static string Replace(this string source, string oldString, 
                             string newString, StringComparison comparison)
{
    int index = source.IndexOf(oldString, comparison);

    while (index > -1)
    {
        source = source.Remove(index, oldString.Length);
        source = source.Insert(index, newString);

        index = source.IndexOf(oldString, index + newString.Length, comparison);
    }

    return source;
}

用法：

string source = "banana";
Console.WriteLine(source.Replace("AN", "banana", StringComparison.OrdinalIgnoreCase));

结果：

bbananabananaa

并且，如果您仍然希望递归性质是可选的：

代码：

public static string Replace(this string source, string oldString, 
                             string newString, StringComparison comparison,
                             bool recursive = true)
{
    int index = source.IndexOf(oldString, comparison);

    while (index > -1)
    {
        source = source.Remove(index, oldString.Length);
        source = source.Insert(index, newString);

        if (!recursive)
        {
            return source;
        }
        index = source.IndexOf(oldString, index + newString.Length, comparison);
    }

    return source;
}

用法：

string source = "banana";
Console.WriteLine(source.Replace("AN", "banana", StringComparison.OrdinalIgnoreCase, false));

结果：

bbananaana

Answer 5

使用 StringComparison，因为它有方便的 OrdinalIgnoreCase

    string sentence = "We know it contains 'camel' word."; 
    string wordToFind = "camel";
    string replacementWord = "horse";

    int index = sentence.IndexOf(wordToFind , StringComparison.OrdinalIgnoreCase)
    // Did we match the word regardless of case
    bool match = index >= 0;

    // perform the replace on the matched word
    if(match) {
        sentence = sentence.Remove(index, wordToFind.Length)
        sentence = sentence.Insert(index, replacementWord)
    }

如果 C# String 类有一个像 Java 一样的 ignoreCase() 方法，那就太好了。

Answer 6

您还可以使用 String.IndexOf

http://msdn.microsoft。 com/en-us/library/system.string.indexof.aspx

与使用 RegExpressions 相比，您可能会获得稍好的性能（我讨厌它们，因为它们不直观且容易搞砸，尽管这简单的.Net 函数调用抽象了实际混乱的正则表达式，并且没有提供太多的错误空间），但这可能不是您关心的问题；现在的电脑真的很快，对吧？ :) 采用 StringComparison 对象的 IndexOf 重载允许您选择忽略大小写，并且由于 IndexOf 返回指定位置的第一个匹配项，因此您必须编写一个循环来处理多次出现的字符串。

Answer 7

    public static string CustomReplace(string srcText, string toFind, string toReplace, bool matchCase, bool replace0nce)
    {
        StringComparison sc = StringComparison.OrdinalIgnoreCase;
        if (matchCase)
            sc = StringComparison.Ordinal;

        int pos;
        while ((pos = srcText.IndexOf(toFind, sc)) > -1)
        {
            srcText = srcText.Remove(pos, toFind.Length);
            srcText = srcText.Insert(pos, toReplace);

            if (replace0nce)
                break;
        }

        return srcText;
    }

Answer 8

它可能不如其他一些答案那么有效，但我有点喜欢 sntbob 编写的 CustomReplace 函数。

然而，它有一个缺陷。如果文本替换是递归的，则会导致无限循环。例如，CustomReplace("I eatbananas!","an","banana",false,false) 将导致无限循环，并且字符串将继续变大。
例如，在第四次迭代之后，字符串将是“I eat bbbbbananaanaanaanaanas!”

如果您只想替换“banana”中“an”的两个实例，那么您将不得不采取另一种方法。我修改了 sntbob 的代码来解决这种情况。我承认它要复杂得多，但它可以处理递归替换。

public static string CustomReplace(string srcText, string toFind, string toReplace, bool matchCase, bool replaceOnce)
    {
        StringComparison sc = StringComparison.OrdinalIgnoreCase;
        if (matchCase)
            sc = StringComparison.Ordinal;

        int pos;
        int previousProcessedLength = 0;
        string alreadyProcessedTxt = "";
        string remainingToProcessTxt = srcText;
        while ((pos = remainingToProcessTxt.IndexOf(toFind, sc)) > -1)
        {
            previousProcessedLength = alreadyProcessedTxt.Length;
            //Append processed text up until the end of the found string and perform replacement
            alreadyProcessedTxt += remainingToProcessTxt.Substring(0, pos + toFind.Length);
            alreadyProcessedTxt = alreadyProcessedTxt.Remove(previousProcessedLength + pos, toFind.Length);
            alreadyProcessedTxt = alreadyProcessedTxt.Insert(previousProcessedLength + pos, toReplace);

            //Remove processed text from remaining
            remainingToProcessTxt = remainingToProcessTxt.Substring(pos + toFind.Length);                

            if (replaceOnce)
                break;
        }

        return alreadyProcessedTxt + remainingToProcessTxt;
    }

Answer 9

为什么不直接导入 Microsoft.VisualBasic 命名空间并使用 VB Strings.Replace 方法？

https://msdn .microsoft.com/en-us/library/microsoft.visualbasic.strings.replace(v=vs.110).aspx

例如，

var newString = Strings.Replace(SourceString, FindTextValue, ReplacementTextValue, 1, -1, Constants.vbTextCompare);

vbTextCompare 强制进行不区分大小写的替换。工作完成了。

好吧，它不是“纯”C#，但它可以让您以更少的复杂性和更少的混乱到达您想要的地方。

Answer 10

这是使用 StringComparison 作为扩展方法的另一种替代方法。在 StringBuilder 对象上。我读过一些文章，表明 StringBuilder 使用内存可能比使用字符串更有效。如果您需要的话，您可以轻松地更改它以使用字符串。

/// <summary>
/// Extension method to find/replace replaces text in a StringBuilder object
/// </summary>
/// <param name="original">Source StringBuilder object</param>
/// <param name="oldString">String to search for</param>
/// <param name="newString">String to replace each occurrance of oldString</param>
/// <param name="stringComparison">String comparison to use</param>
/// <returns>Original Stringbuilder with replacements made</returns>
public static StringBuilder Replace(this StringBuilder original,
                    string oldString, string newString, StringComparison stringComparison)
    {
        //If anything is null, or oldString is blank, exit with original value
        if ( newString == null || original == null || string.IsNullOrEmpty(oldString))
            return original;

        //Convert to a string and get starting position using
        //IndexOf which allows us to use StringComparison.
        int pos = original.ToString().IndexOf(oldString, 0, stringComparison);

        //Loop through until we find and replace all matches
        while ( pos >= 0 )
        {
            //Remove the old string and insert the new one.
            original.Remove(pos, oldString.Length).Insert(pos, newString);

            //Get the next match starting 1 character after last replacement (to avoid a possible infinite loop)
            pos = original.ToString().IndexOf(oldString, pos + newString.Length + 1, stringComparison);
        }
        return original;
    }