如何在 C# 中使用 Substring() 获取字符串的最后五个字符？

Question

I can get the first three characters with the function below.

However, how can I get the output of the last five characters ("Three") with the Substring() function? Or will another string function have to be used?

static void Main()
{
    string input = "OneTwoThree";

    // Get first three characters
    string sub = input.Substring(0, 3);
    Console.WriteLine("Substring: {0}", sub); // Output One. 
}

Answer 1

If your input string could be less than five characters long then you should be aware that string.Substring will throw an ArgumentOutOfRangeException if the startIndex argument is negative.

To solve this potential problem you can use the following code:

string sub = input.Substring(Math.Max(0, input.Length - 5));

Or more explicitly:

public static string Right(string input, int length)
{
    if (length >= input.Length)
    {
        return input;
    }
    else
    {
        return input.Substring(input.Length - length);
    }
}

Answer 2

string sub = input.Substring(input.Length - 5);

Answer 3

If you can use extension methods, this will do it in a safe way regardless of string length:

public static string Right(this string text, int maxLength)
{
    if (string.IsNullOrEmpty(text) || maxLength <= 0)
    {
        return string.Empty;
    }

    if (maxLength < text.Length)
    {
        return text.Substring(text.Length - maxLength);
    }

    return text;
}

And to use it:

string sub = input.Right(5);

Answer 4

static void Main()
    {
        string input = "OneTwoThree";

            //Get last 5 characters
        string sub = input.Substring(6);
        Console.WriteLine("Substring: {0}", sub); // Output Three. 
    }

• Substring(0, 3) - Returns substring of first 3 chars. //One

• Substring(3, 3) - Returns substring of second 3 chars. //Two

• Substring(6) - Returns substring of all chars after first 6. //Three

Answer 5

一种方法是使用字符串的Length属性作为Substring输入的一部分：

string sub = input.Substring(input.Length - 5); // Retrieves the last 5 characters of input

Answer 6

Here is a quick extension method you can use that mimics PHP syntax. Include AssemblyName.Extensions to the code file you are using the extension in.

Then you could call:

input.SubstringReverse(-5) and it will return "Three".

namespace AssemblyName.Extensions {

    public static class StringExtensions
    {
        /// <summary>
        /// Takes a negative integer - counts back from the end of the string.
        /// </summary>
        /// <param name="str"></param>
        /// <param name="length"></param>
        public static string SubstringReverse(this string str, int length)
        {
            if (length > 0) 
            {
                throw new ArgumentOutOfRangeException("Length must be less than zero.");
            }

            if (str.Length < Math.Abs(length))
            {
                throw new ArgumentOutOfRangeException("Length cannot be greater than the length of the string.");
            }

            return str.Substring((str.Length + length), Math.Abs(length));
        }
    }
}

Answer 7

Substring. This method extracts strings. It requires the location of the substring (a start index, a length). It then returns a new string with the characters in that range.

See a small example :

string input = "OneTwoThree";
// Get first three characters.
string sub = input.Substring(0, 3);
Console.WriteLine("Substring: {0}", sub);

Output : Substring: One

Answer 8

eg

string str = null;
string retString = null;
str = "This is substring test";
retString = str.Substring(8, 9);

This return "substring"

C# substring sample source

Answer 9

simple way to do this in one line of code would be this

string sub = input.Substring(input.Length > 5 ? input.Length - 5 : 0);

and here some informations about Operator ? :

Answer 10

string input = "OneTwoThree";
(if input.length >5)
{
string str=input.substring(input.length-5,5);
}

Answer 11

In C# 8.0 and later you can use [^5..] to get the last five characters combined with a ? operator to avoid a potential ArgumentOutOfRangeException .

string input1 = "0123456789";
string input2 = "0123";
Console.WriteLine(input1.Length >= 5 ? input1[^5..] : input1); //returns 56789
Console.WriteLine(input2.Length >= 5 ? input2[^5..] : input2); //returns 0123

index-from-end-operator and range-operator

Answer 12

// Get first three characters
string sub = input.Substring(0, 3);
Console.WriteLine("Substring: {0}", sub); // Output One. 

string sub = input.Substring(6, 5);
Console.WriteLine("Substring: {0}", sub); //You'll get output: Three