Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Make first letter of a string upper case (with maximum performance)

Tags:

performance

c#

People also ask

How can I uppercase the first letter of a string?

To capitalize the first character of a string, We can use the charAt() to separate the first character and then use the toUpperCase() function to capitalize it.

Which function converts the first character to upper case?

The ucfirst() method takes an input string and converts its first character to the uppercase, if it is a lower case alphabetic character.

What is the correct way to convert a string into upper case?

Java String toUpperCase() Method The toUpperCase() method converts a string to upper case letters.

How do you make the first letter of a string uppercase in Python?

How do you capitalize the first letter of a string? The first letter of a string can be capitalized using the capitalize() function. This method returns a string with the first letter capitalized. If you are looking to capitalize the first letter of the entire string the title() function should be used.


Solution in different C# versions

C# 8 with at least .NET Core 3.0 or .NET Standard 2.1

public static class StringExtensions
{
    public static string FirstCharToUpper(this string input) =>
        input switch
        {
            null => throw new ArgumentNullException(nameof(input)),
            "" => throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input)),
            _ => string.Concat(input[0].ToString().ToUpper(), input.AsSpan(1))
        };
}

Since .NET Core 3.0 / .NET Standard 2.1 String.Concat() supports ReadonlySpan<char> which saves one allocation if we use .AsSpan(1) instead of .Substring(1).

C# 8

public static class StringExtensions
{
    public static string FirstCharToUpper(this string input) =>
        input switch
        {
            null => throw new ArgumentNullException(nameof(input)),
            "" => throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input)),
            _ => input[0].ToString().ToUpper() + input.Substring(1)
        };
}

C# 7

public static class StringExtensions
{
    public static string FirstCharToUpper(this string input)
    {
        switch (input)
        {
            case null: throw new ArgumentNullException(nameof(input));
            case "": throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input));
            default: return input[0].ToString().ToUpper() + input.Substring(1);
        }
    }
}

Really old answers

public static string FirstCharToUpper(string input)
{
    if (String.IsNullOrEmpty(input))
        throw new ArgumentException("ARGH!");
    return input.First().ToString().ToUpper() + String.Join("", input.Skip(1));
}

This version is shorter. For a faster solution, take a look at Diego's answer.

public static string FirstCharToUpper(string input)
{
    if (String.IsNullOrEmpty(input))
        throw new ArgumentException("ARGH!");
    return input.First().ToString().ToUpper() + input.Substring(1);
}

Probably the fastest solution is Darren's (There's even a benchmark) although I would change it's string.IsNullOrEmpty(s) validation to throw an exception since the original requirement expects for a first letter to exist so it can be uppercased. Note that this code works for a generic string and not particularly on valid values from the Textbox.


public string FirstLetterToUpper(string str)
{
    if (str == null)
        return null;

    if (str.Length > 1)
        return char.ToUpper(str[0]) + str.Substring(1);

    return str.ToUpper();
}

Old answer: This makes every first letter to upper case

public string ToTitleCase(string str)
{
    return CultureInfo.CurrentCulture.TextInfo.ToTitleCase(str.ToLower());
}

The right way is to use Culture:

System.Globalization.CultureInfo.CurrentCulture.TextInfo.ToTitleCase(word.ToLower())

Note: This will capitalise each word within a string, e.g. "red house" --> "Red House". The solution will also lower-case capitalisation within words, e.g. "old McDonald" --> "Old Mcdonald".


I took the fastest method from C# Uppercase First Letter - Dot Net Perls and converted to an extension method:

    /// <summary>
    /// Returns the input string with the first character converted to uppercase, or mutates any nulls passed into string.Empty
    /// </summary>
    public static string FirstLetterToUpperCaseOrConvertNullToEmptyString(this string s)
    {
        if (string.IsNullOrEmpty(s))
            return string.Empty;

        char[] a = s.ToCharArray();
        a[0] = char.ToUpper(a[0]);
        return new string(a);
    }

NOTE: The reason using ToCharArray is faster than the alternative char.ToUpper(s[0]) + s.Substring(1), is that only one string is allocated, whereas the Substring approach allocates a string for the substring, and then a second string to compose the final result.


Here is what this approach looks like, combined with the initial test from CarlosMuñoz's accepted answer:

    /// <summary>
    /// Returns the input string with the first character converted to uppercase
    /// </summary>
    public static string FirstLetterToUpperCase(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);
    }