我有一个字符串叫做"hello world"
我需要将单词"world"替换为"csharp"
我使用以下代码实现:
string.Replace("World", "csharp");
但是结果是,我没有得到被替换的字符串。原因是大小写敏感。原始字符串包含了 "world",而我尝试替换的是 "World"。
有没有办法避免 string.Replace 方法的大小写敏感性?
我有一个字符串叫做"hello world"
我需要将单词"world"替换为"csharp"
我使用以下代码实现:
string.Replace("World", "csharp");
但是结果是,我没有得到被替换的字符串。原因是大小写敏感。原始字符串包含了 "world",而我尝试替换的是 "World"。
有没有办法避免 string.Replace 方法的大小写敏感性?
你可以使用正则表达式进行不区分大小写的替换:
class Program
{
static void Main()
{
string input = "hello WoRlD";
string result =
Regex.Replace(input, "world", "csharp", RegexOptions.IgnoreCase);
Console.WriteLine(result); // prints "hello csharp"
}
}
hello. world?
或任何其他包含正则表达式运算符的内容。 - Sebastian Machvar search = "world";
var replacement = "csharp";
string result = Regex.Replace(
stringToLookInto,
Regex.Escape(search),
replacement.Replace("$","$$"),
RegexOptions.IgnoreCase
);
Regex.Escape方法非常有用,如果你使用了用户输入,其中可能包含正则表达式语言元素。
更新
根据评论,实际上您不必对替换字符串进行转义。
using System;
using System.Text.RegularExpressions;
public class Program
{
public static void Main()
{
var tests = new[] {
new { Input="abcdef", Search="abc", Replacement="xyz", Expected="xyzdef" },
new { Input="ABCdef", Search="abc", Replacement="xyz", Expected="xyzdef" },
new { Input="A*BCdef", Search="a*bc", Replacement="xyz", Expected="xyzdef" },
new { Input="abcdef", Search="abc", Replacement="x*yz", Expected="x*yzdef" },
new { Input="abcdef", Search="abc", Replacement="$", Expected="$def" },
};
foreach(var test in tests){
var result = ReplaceCaseInsensitive(test.Input, test.Search, test.Replacement);
Console.WriteLine(
"Success: {0}, Actual: {1}, {2}",
result == test.Expected,
result,
test
);
}
}
private static string ReplaceCaseInsensitive(string input, string search, string replacement){
string result = Regex.Replace(
input,
Regex.Escape(search),
replacement.Replace("$","$$"),
RegexOptions.IgnoreCase
);
return result;
}
}
它的输出结果是:
Success: True, Actual: xyzdef, { Input = abcdef, Search = abc, Replacement = xyz, Expected = xyzdef }
Success: True, Actual: xyzdef, { Input = ABCdef, Search = abc, Replacement = xyz, Expected = xyzdef }
Success: True, Actual: xyzdef, { Input = A*BCdef, Search = a*bc, Replacement = xyz, Expected = xyzdef }
Success: True, Actual: x*yzdef, { Input = abcdef, Search = abc, Replacement = x*yz, Expected = x*yzdef}
Success: True, Actual: $def, { Input = abcdef, Search = abc, Replacement = $, Expected = $def }
比其他正则表达式方法快2.5倍,并且最有效:
/// <summary>
/// Returns a new string in which all occurrences of a specified string in the current instance are replaced with another
/// specified string according the type of search to use for the specified string.
/// </summary>
/// <param name="str">The string performing the replace method.</param>
/// <param name="oldValue">The string to be replaced.</param>
/// <param name="newValue">The string replace all occurrences of <paramref name="oldValue"/>.
/// If value is equal to <c>null</c>, than all occurrences of <paramref name="oldValue"/> will be removed from the <paramref name="str"/>.</param>
/// <param name="comparisonType">One of the enumeration values that specifies the rules for the search.</param>
/// <returns>A string that is equivalent to the current string except that all instances of <paramref name="oldValue"/> are replaced with <paramref name="newValue"/>.
/// If <paramref name="oldValue"/> is not found in the current instance, the method returns the current instance unchanged.</returns>
[DebuggerStepThrough]
public static string Replace(this string str,
string oldValue, string newValue,
StringComparison comparisonType)
{
// Check inputs.
if (str == null)
{
// Same as original .NET C# string.Replace behavior.
throw new ArgumentNullException(nameof(str));
}
if (oldValue == null)
{
// Same as original .NET C# string.Replace behavior.
throw new ArgumentNullException(nameof(oldValue));
}
if (oldValue.Length == 0)
{
// Same as original .NET C# string.Replace behavior.
throw new ArgumentException("String cannot be of zero length.");
}
if (str.Length == 0)
{
// Same as original .NET C# string.Replace behavior.
return str;
}
//if (oldValue.Equals(newValue, comparisonType))
//{
//This condition has no sense
//It will prevent method from replacesing: "Example", "ExAmPlE", "EXAMPLE" to "example"
//return str;
//}
// Prepare string builder for storing the processed string.
// Note: StringBuilder has a better performance than String by 30-40%.
StringBuilder resultStringBuilder = new StringBuilder(str.Length);
// Analyze the replacement: replace or remove.
bool isReplacementNullOrEmpty = string.IsNullOrEmpty(newValue);
// Replace all values.
const int valueNotFound = -1;
int foundAt;
int startSearchFromIndex = 0;
while ((foundAt = str.IndexOf(oldValue, startSearchFromIndex, comparisonType)) != valueNotFound)
{
// Append all characters until the found replacement.
int charsUntilReplacment = foundAt - startSearchFromIndex;
bool isNothingToAppend = charsUntilReplacment == 0;
if (!isNothingToAppend)
{
resultStringBuilder.Append(str, startSearchFromIndex, charsUntilReplacment);
}
// Process the replacement.
if (!isReplacementNullOrEmpty)
{
resultStringBuilder.Append(newValue);
}
// Prepare start index for the next search.
// This needed to prevent infinite loop, otherwise method always start search
// from the start of the string. For example: if an oldValue == "EXAMPLE", newValue == "example"
// and comparisonType == "any ignore case" will conquer to replacing:
// "EXAMPLE" to "example" to "example" to "example" … infinite loop.
startSearchFromIndex = foundAt + oldValue.Length;
if (startSearchFromIndex == str.Length)
{
// It is end of the input string: no more space for the next search.
// The input string ends with a value that has already been replaced.
// Therefore, the string builder with the result is complete and no further action is required.
return resultStringBuilder.ToString();
}
}
// Append the last part to the result.
int charsUntilStringEnd = str.Length - startSearchFromIndex;
resultStringBuilder.Append(str, startSearchFromIndex, charsUntilStringEnd);
return resultStringBuilder.ToString();
}
注意:在StringComparison comparisonType
参数中使用StringComparison.OrdinalIgnoreCase
,忽略大小写。这是最快的、不区分大小写的替换所有值的方法。
这种方法的优点:
newValue
设置为null
),针对此进行了优化;string.Replace
行为相同,同样有异常;@AsValeO:不适用于Regex语言元素,因此不是通用方法
@Mike Stillion:这段代码存在问题。如果新文本是旧文本的超集,这可能会产生无限循环。
基准测试证明:这个解决方案比@Steve B.的正则表达式快2.59倍,代码如下:
// Results:
// 1/2. Regular expression solution: 4486 milliseconds
// 2/2. Current solution: 1727 milliseconds — 2.59X times FASTER! than regex!
// Notes: the test was started 5 times, the result is an average; release build.
const int benchmarkIterations = 1000000;
const string sourceString = "aaaaddsdsdsdsdsd";
const string oldValue = "D";
const string newValue = "Fod";
long totalLenght = 0;
Stopwatch regexStopwatch = Stopwatch.StartNew();
string tempString1;
for (int i = 0; i < benchmarkIterations; i++)
{
tempString1 = sourceString;
tempString1 = ReplaceCaseInsensitive(tempString1, oldValue, newValue);
totalLenght = totalLenght + tempString1.Length;
}
regexStopwatch.Stop();
Stopwatch currentSolutionStopwatch = Stopwatch.StartNew();
string tempString2;
for (int i = 0; i < benchmarkIterations; i++)
{
tempString2 = sourceString;
tempString2 = tempString2.Replace(oldValue, newValue,
StringComparison.OrdinalIgnoreCase);
totalLenght = totalLenght + tempString2.Length;
}
currentSolutionStopwatch.Stop();
原始想法 - @Darky711;感谢@MinerR提供StringBuilder
。
String
。然而,StringBuilder
比 String
快 **30-40%**。我已经更新了解决方案。谢谢 ;) - Oleg Zarevennyi有很多建议使用正则表达式。那么不用它的扩展方法如何:
public static string Replace(this string str, string old, string @new, StringComparison comparison)
{
@new = @new ?? "";
if (string.IsNullOrEmpty(str) || string.IsNullOrEmpty(old) || old.Equals(@new, comparison))
return str;
int foundAt = 0;
while ((foundAt = str.IndexOf(old, foundAt, comparison)) != -1)
{
str = str.Remove(foundAt, old.Length).Insert(foundAt, @new);
foundAt += @new.Length;
}
return str;
}
if(old.Equals(@new, comparison)) return @new;
,因为新字符串可能在大小写方面有所不同。 - sɐunıɔןɐqɐp扩展程序使我们的生活更轻松:
static public class StringExtensions
{
static public string ReplaceInsensitive(this string str, string from, string to)
{
str = Regex.Replace(str, from, to, RegexOptions.IgnoreCase);
return str;
}
}
.Net Core内置了这个方法:Replace(String, String, StringComparison)
文档。现在我们可以简单地写:
"...".Replace("oldValue", "newValue", StringComparison.OrdinalIgnoreCase)
Replace(sourceString, "replacethis", "withthis", , , CompareMethod.Text)
修改了 @Darky711 的答案,使用传递进来的比较类型,并尽可能与框架中的替换命名和 xml 注释匹配。
/// <summary>
/// Returns a new string in which all occurrences of a specified string in the current instance are replaced with another specified string.
/// </summary>
/// <param name="str">The string performing the replace method.</param>
/// <param name="oldValue">The string to be replaced.</param>
/// <param name="newValue">The string replace all occurrances of oldValue.</param>
/// <param name="comparisonType">Type of the comparison.</param>
/// <returns></returns>
public static string Replace(this string str, string oldValue, string @newValue, StringComparison comparisonType)
{
@newValue = @newValue ?? string.Empty;
if (string.IsNullOrEmpty(str) || string.IsNullOrEmpty(oldValue) || oldValue.Equals(@newValue, comparisonType))
{
return str;
}
int foundAt;
while ((foundAt = str.IndexOf(oldValue, 0, comparisonType)) != -1)
{
str = str.Remove(foundAt, oldValue.Length).Insert(foundAt, @newValue);
}
return str;
}
(编辑:不知道“裸露的链接”问题,对此感到抱歉)
源自这里:
string myString = "find Me and replace ME";
string strReplace = "me";
myString = Regex.Replace(myString, "me", strReplace, RegexOptions.IgnoreCase);
看起来你不是第一个抱怨缺乏不区分大小写的字符串替换功能的人。
public static class ExtensionMethodsString
{
public static string Replace(this String thisString, string oldValue, string newValue, StringComparison stringComparison)
{
string working = thisString;
int index = working.IndexOf(oldValue, stringComparison);
while (index != -1)
{
working = working.Remove(index, oldValue.Length);
working = working.Insert(index, newValue);
index = index + newValue.Length;
index = working.IndexOf(oldValue, index, stringComparison);
}
return working;
}
}