我有一个带有文本框的DetailsView
我希望输入的数据总是以大写的第一个字母保存。
例子:
"red" --> "Red"
"red house" --> " Red house"
我怎样才能实现性能最大化呢?
注意:
Based on the answers and the comments under the answers, many people think this is asking about capitalizing all words in the string. E.g. => Red House It isn't, but if that is what you seek, look for one of the answers that uses TextInfo's ToTitleCase method. (Note: Those answers are incorrect for the question actually asked.)
See TextInfo.ToTitleCase documentation for caveats (doesn't touch all-caps words - they are considered acronyms; may lowercase letters in middle of words that "shouldn't" be lowered, e.g., "McDonald" → "Mcdonald"; not guaranteed to handle all culture-specific subtleties re capitalization rules.)
注意:
第一个字母之后的字母是否必须小写，这个问题很模糊。公认的答案假定只有第一个字母需要修改。如果要强制字符串中除第一个字母外的所有字母都小写，请查找包含ToLower且不包含ToTitleCase的答案。
由于这个问题是关于最大化性能的，我采用了Darren的版本来使用跨度，这减少了垃圾，并提高了大约10%的速度。
/// <summary>
/// Returns the input string with the first character converted to uppercase
/// </summary>
public static string ToUpperFirst(this string s)
{
if (string.IsNullOrEmpty(s))
throw new ArgumentException("There is no first letter");
Span<char> a = stackalloc char[s.Length];
s.AsSpan(1).CopyTo(a.Slice(1));
a[0] = char.ToUpper(s[0]);
return new string(a);
}
性能
| Method |
Data |
Mean |
Error |
StdDev |
| Carlos |
red |
107.29 ns |
2.2401 ns |
3.9234 ns |
| Darren |
red |
30.93 ns |
0.9228 ns |
0.8632 ns |
| Marcell |
red |
26.99 ns |
0.3902 ns |
0.3459 ns |
| Carlos |
red house |
106.78 ns |
1.9713 ns |
1.8439 ns |
| Darren |
red house |
32.49 ns |
0.4253 ns |
0.3978 ns |
| Marcell |
red house |
27.37 ns |
0.3888 ns |
0.3637 ns |
完整的测试代码
using System;
using System.Linq;
using BenchmarkDotNet.Attributes;
namespace CorePerformanceTest
{
public class StringUpperTest
{
[Params("red", "red house")]
public string Data;
[Benchmark]
public string Carlos() => Data.Carlos();
[Benchmark]
public string Darren() => Data.Darren();
[Benchmark]
public string Marcell() => Data.Marcell();
}
internal static class StringExtensions
{
public static string Carlos(this string input) =>
input switch
{
null => throw new ArgumentNullException(nameof(input)),
"" => throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input)),
_ => input.First().ToString().ToUpper() + input.Substring(1)
};
public static string Darren(this string s)
{
if (string.IsNullOrEmpty(s))
throw new ArgumentException("There is no first letter");
char[] a = s.ToCharArray();
a[0] = char.ToUpper(a[0]);
return new string(a);
}
public static string Marcell(this string s)
{
if (string.IsNullOrEmpty(s))
throw new ArgumentException("There is no first letter");
Span<char> a = stackalloc char[s.Length];
s.AsSpan(1).CopyTo(a.Slice(1));
a[0] = char.ToUpper(s[0]);
return new string(a);
}
}
}
使用string.Create()并在方法中避免使用throw关键字(是的，您没有看错)，我们可以进一步采用Marcell的答案。此外，我的方法处理任意长度的字符串(例如，几兆字节的文本)。
public static string L33t(this string s)
{
static void ThrowError() => throw new ArgumentException("There is no first letter");
if (string.IsNullOrEmpty(s))
ThrowError(); // No "throw" keyword to avoid costly IL
return string.Create(s.Length, s, (chars, state) =>
{
state.AsSpan().CopyTo(chars); // No slicing to save some CPU cycles
chars[0] = char.ToUpper(chars[0]);
});
}
性能
下面是在。net Core 3.1.7 64位上运行的基准测试的数据。我添加了一个更长的字符串，以精确计算额外拷贝的成本。
| Method |
Data |
Mean |
Error |
StdDev |
Median |
| L33t |
red |
8.545 ns |
0.4612 ns |
1.3308 ns |
8.075 ns |
| Marcell |
red |
9.153 ns |
0.3377 ns |
0.9471 ns |
8.946 ns |
| L33t |
red house |
7.715 ns |
0.1741 ns |
0.4618 ns |
7.793 ns |
| Marcell |
red house |
10.537 ns |
0.5002 ns |
1.4351 ns |
10.377 ns |
| L33t |
red r(...)house [89] |
11.121 ns |
0.6774 ns |
1.9106 ns |
10.612 ns |
| Marcell |
red r(...)house [89] |
16.739 ns |
0.4468 ns |
1.3033 ns |
16.853 ns |
完整的测试代码
using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
namespace CorePerformanceTest
{
class Program
{
static void Main(string[] args)
{
var summary = BenchmarkRunner.Run<StringUpperTest>();
}
}
public class StringUpperTest
{
[Params("red", "red house", "red red red red red red red red red red red red red red red red red red red red red house")]
public string Data;
[Benchmark]
public string Marcell() => Data.Marcell();
[Benchmark]
public string L33t() => Data.L33t();
}
internal static class StringExtensions
{
public static string Marcell(this string s)
{
if (string.IsNullOrEmpty(s))
throw new ArgumentException("There is no first letter");
Span<char> a = stackalloc char[s.Length];
s.AsSpan(1).CopyTo(a.Slice(1));
a[0] = char.ToUpper(s[0]);
return new string(a);
}
public static string L33t(this string s)
{
static void ThrowError() => throw new ArgumentException("There is no first letter");
if (string.IsNullOrEmpty(s))
ThrowError(); // IMPORTANT: Do not "throw" here!
return string.Create(s.Length, s, (chars, state) =>
{
state.AsSpan().CopyTo(chars);
chars[0] = char.ToUpper(chars[0]);
});
}
}
}
如果你能让它更快，请告诉我!
