使字符串的第一个字母大写(以最大性能)

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。

当前回答

使用以下代码:

string strtest ="PRASHANT";
strtest.First().ToString().ToUpper() + strtest.Remove(0, 1).ToLower();

2013-08-26 12:32:28

其他回答

string input = "red HOUSE";
System.Text.StringBuilder sb = new System.Text.StringBuilder(input);

for (int j = 0; j < sb.Length; j++)
{
    if ( j == 0 ) //catches just the first letter
        sb[j] = System.Char.ToUpper(sb[j]);
    else  //everything else is lower case
        sb[j] = System.Char.ToLower(sb[j]);
}
// Store the new string.
string corrected = sb.ToString();
System.Console.WriteLine(corrected);

2010-11-09 15:33:34

使用以下代码:

string strtest ="PRASHANT";
strtest.First().ToString().ToUpper() + strtest.Remove(0, 1).ToLower();

2013-08-26 12:32:28

用这种方法，你可以把每个单词的第一个字符抬高。

例子

"HeLlo wOrld" => "HeLlo wOrld"

public static string FirstCharToUpper(string input)
{
    if (String.IsNullOrEmpty(input))
        throw new ArgumentException("Error");
    return string.Join(" ", input.Split(' ').Select(d => d.First().ToString().ToUpper() +  d.ToLower().Substring(1)));
}

2013-10-01 13:50:39

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);
        }
    }

}

2020-02-28 18:47:05

我认为下面的方法是最好的解决方案。

class Program
{
    static string UppercaseWords(string value)
    {
        char[] array = value.ToCharArray();
        // Handle the first letter in the string.
        if (array.Length >= 1)
        {
            if (char.IsLower(array[0]))
            {
                array[0] = char.ToUpper(array[0]);
            }
        }
        // Scan through the letters, checking for spaces.
        // ... Uppercase the lowercase letters following spaces.
        for (int i = 1; i < array.Length; i++)
        {
            if (array[i - 1] == ' ')
            {
                if (char.IsLower(array[i]))
                {
                    array[i] = char.ToUpper(array[i]);
                }
            }
        }
        return new string(array);
    }

    static void Main()
    {
        // Uppercase words in these strings.
        const string value1 = "something in the way";
        const string value2 = "dot net PERLS";
        const string value3 = "String_two;three";
        const string value4 = " sam";
        // ... Compute the uppercase strings.
        Console.WriteLine(UppercaseWords(value1));
        Console.WriteLine(UppercaseWords(value2));
        Console.WriteLine(UppercaseWords(value3));
        Console.WriteLine(UppercaseWords(value4));
    }
}

Output

Something In The Way
Dot Net PERLS
String_two;three
 Sam

参考

2018-10-29 00:45:48

使字符串的第一个字母大写(以最大性能)

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