string中Insert与Format效率对比、String与List中Contains与IndexOf的效率对比(二)
public int IndexOf(String value, StringComparison comparisonType) {
return IndexOf(value, 0, this.Length, comparisonType);
}
public int IndexOf(String value, int startIndex, StringComparison comparisonType) {
return IndexOf(value, startIndex, this.Length - startIndex, comparisonType);
}
public int IndexOf(String value, int startIndex, int count, StringComparison comparisonType) {
// Validate inputs
if (value == null)
throw new ArgumentNullException("value");
if (startIndex < 0 || startIndex > this.Length)
throw new ArgumentOutOfRangeException("startIndex", Environment.GetResourceString("ArgumentOutOfRange_Index"));
if (count < 0 || startIndex > this.Length - count)
throw new ArgumentOutOfRangeException("count",Environment.GetResourceString("ArgumentOutOfRange_Count"));
switch (comparisonType) {
case StringComparison.CurrentCulture:
return CultureInfo.CurrentCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.None);
case StringComparison.CurrentCultureIgnoreCase:
return CultureInfo.CurrentCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.IgnoreCase);
case StringComparison.InvariantCulture:
return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.None);
case StringComparison.InvariantCultureIgnoreCase:
return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.IgnoreCase);
case StringComparison.Ordinal:
return CultureInfo.InvariantCulture.CompareInfo.IndexOf(this, value, startIndex, count, CompareOptions.Ordinal);
case StringComparison.OrdinalIgnoreCase:
return TextInfo.IndexOfStringOrdinalIgnoreCase(this, value, startIndex, count);
default:
throw new ArgumentException(Environment.GetResourceString("NotSupported_StringComparison"), "comparisonType");
}
}
结论差不多出来了吧，不过这里还牵扯到另一个类CultureInfo.InvariantCulture.CompareInfo，我也看过该类的代码，里头有unsafe代码，不在本文范畴，但是有个结论就是当把我的Demo里的代码的IndexOf改为“x.IndexOf(y, StringComparison.Ordinal)”，那么他们俩的相率将相差无二。
这里没有牵扯到正则匹配以及LastIndexOf，其实正则匹配有时可能效率比上述方式更高，但是要视场景使用，更通用的方式还是建议“IndexOf(value, StringComparison.Ordinal)”或“Contains”方法。
string其本身就是char数组的封装，其或多或少体现着Array的一些特点，那么接下来再来看看在List集合中的关于Contains与IndexOf的情况。