快速替换字符串c#
在.NET中字符串替换有以下五种⽅法：
1：使⽤String.Replace函数替换，但不⽀持⼤⼩写。
2：正则System.Text.Regex 替换，⽤RegExpOption修改是否⽀持⼤⼩写。
3：在⼩数据的情况下，使⽤String.SubString 和+可以实现间接替换。
4：导⼊Microsoft Visual Basic RunTime (Microsoft.VisualBasic.DLL) 使⽤Strings.Replace速度很快。5：参照反射Reflector.FileDisassembler配合Strings.Split and Strings.Join 等实现，速度同5。
⼀下介绍⼀种算法，类似KMP算法。有兴趣的参照研究下。
private static string ReplaceEx(string original,
string pattern, string replacement)
{
int count, position0, position1;
count = position0 = position1 = 0;
string upperString = original.ToUpper();
string upperPattern = pattern.ToUpper();
int inc = (original.Length/pattern.Length) *
(replacement.Length-pattern.Length);
char [] chars = new char[original.Length + Math.Max(0, inc)];
while( (position1 = upperString.IndexOf(upperPattern,
position0)) != -1 )
{
for ( int i=position0 ; i < position1 ; ++i )
chars[count++] = original[i];
for ( int i=0 ; i < replacement.Length ; ++i )
chars[count++] = replacement[i];
position0 = position1+pattern.Length;
}
if ( position0 == 0 ) return original;
for ( int i=position0 ; i < original.Length ; ++i )
chars[count++] = original[i];
return new string(chars, 0, count);
}
测试
static void Main(string[] args)
{
string segment = "AaBbCc";
string source;
string pattern = "AbC";
string destination = "Some";
string result = "";
const long count = 1000;
StringBuilder pressure = new StringBuilder();
HiPerfTimer time;
字符串replace函数
for (int i = 0; i < count; i++)
{
pressure.Append(segment);
}
source = pressure.ToString();
GC.Collect();
//regexp
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = Regex.Replace(source, pattern,
destination, RegexOptions.IgnoreCase);
}
time.Stop();
Console.WriteLine("regexp    = " + time.Duration + "s");
GC.Collect();
//vb
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = Strings.Replace(source, pattern,
destination, 1, -1, CompareMethod.Text);
}
time.Stop();
Console.WriteLine("vb        = " + time.Duration + "s");
GC.Collect();
//vbReplace
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = VBString.Replace(source, pattern,
destination, 1, -1, StringCompareMethod.Text);
}
time.Stop();
Console.WriteLine("vbReplace = " + time.Duration + "s");// + result);    GC.Collect();
// ReplaceEx
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = Test.ReplaceEx(source, pattern, destination);
}
time.Stop();
Console.WriteLine("ReplaceEx = " + time.Duration + "s");
GC.Collect();
// Replace
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = source.Replace(pattern.ToLower(), destination);    }
time.Stop();
Console.WriteLine("Replace  = " + time.Duration + "s");
GC.Collect();
/
/sorry, two slow :(
/*//substring
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = StringHelper.ReplaceText(source, pattern,
destination, StringHelper.CompareMethods.Text);    }
time.Stop();
Console.WriteLine("substring =" + time.Duration + ":");
GC.Collect();
/
/substring with stringbuilder
time = new HiPerfTimer();
time.Start();
for (int i = 0; i < count; i++)
{
result = StringHelper.ReplaceTextB(source, pattern,
destination, StringHelper.CompareMethods.Text);    }
time.Stop();
Console.WriteLine("substringB=" + time.Duration + ":");
GC.Collect();
*/
Console.ReadLine();
}
1¡¢string segment = "abcaBc";
regexp = 3.75481827997692s
vb = 1.52745502570857s
vbReplace = 1.46234256029747s
ReplaceEx = 0.797071415501132s <FONT color=gray>Replace = 0.178327413120941s </FONT>
// ReplaceEx > vbReplace > vb > regexp
2¡¢string segment = "abcaBcabC";
regexp = 5.30117431126023s
vb = 2.46258449048692s
vbReplace = 2.5018721653171s
ReplaceEx = 1.00662179131705s
<FONT color=gray>Replace = 0.233760994763301s </FONT>
// ReplaceEx > vb > vbReplace > regexp
3¡¢string segment = "abcaBcabCAbc";
regexp = 7.00987862982586s
vb = 3.61050301085753s
vbReplace = 3.42324876485699s
ReplaceEx = 1.14969947297771s
<FONT color=gray>Replace = 0.277254511397398s </FONT>
// ReplaceEx > vbReplace > vb > regexp
4¡¢string segment = "ABCabcAbCaBcAbcabCABCAbcaBC";
regexp = 13.5940090151123s
vb = 11.6806222578568s
vbReplace = 11.1757614445411s
ReplaceEx = 1.70264153684337s (my god!)
<FONT color=gray>Replace = 0.42236820601501s</FONT>
// ReplaceEx > vbReplace > vb > regexp
查看程序的Block在：
string upperString = original.ToUpper();
string upperPattern = pattern.ToUpper();
如果需要敏感，就免了这2⾏。
解释：先建⼀个char[]类型的变量采访替换后的字符，其⼤⼩就是最⼤可能被替换的字符，例如ABABAB，替换AB成C，其获取过程就是ABABAB最⼤可能包括的AB的数⽬乘以AB多于C的数⽬，
char [] chars = new char[original.Length + Math.Max(0, inc)];
，inc不⼀定⼤于零。
然后循环，⽤IndexOf索引。赋值。。。判断，返回。

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