字符串的前n个字符，即使它比n短？

Question

假设我有字符串s。如果s短于n个字符，我想返回s，否则返回s.Substring(0, n)。

这样做的最简单方法是什么？

Answer 1

我知道的最快方法是：

var result = s.Length < n ? s : s.Substring(0, n); 

Answer 2

最好的办法是写一对夫妇的扩展方法。

然后，你可以使用它像string result = sourceString.Left(10);

public static class StringExt 
{ 
    /// <summary> 
    /// Returns the first <paramref name="count"/> characters of a string, or the entire string if it 
    /// is less than <paramref name="count"/> characters long. 
    /// </summary> 
    /// <param name="self">The string. Cannot be null.</param> 
    /// <param name="count">The number of characters to return.</param> 
    /// <returns>The first <paramref name="count"/> characters of the string.</returns> 

    public static string Left(this string self, int count) 
    { 
     Contract.Requires(self != null); 
     Contract.Requires(count >= 0); 

     Contract.Ensures(Contract.Result<string>() != null); 
     // ReSharper disable PossibleNullReferenceException 
     Contract.Ensures(Contract.Result<string>().Length <= count); 
     // ReSharper restore PossibleNullReferenceException 

     if (self.Length <= count) 
      return self; 
     else 
      return self.Substring(0, count); 
    } 

    /// <summary> 
    /// Returns the last <paramref name="count"/> characters of a string, or the entire string if it 
    /// is less than <paramref name="count"/> characters long. 
    /// </summary> 
    /// <param name="self">The string. Cannot be null.</param> 
    /// <param name="count">The number of characters to return.</param> 
    /// <returns>The last <paramref name="count"/> characters of the string.</returns> 

    public static string Right(this string self, int count) 
    { 
     Contract.Requires(self != null); 
     Contract.Requires(count >= 0); 

     Contract.Ensures(Contract.Result<string>() != null); 
     // ReSharper disable PossibleNullReferenceException 
     Contract.Ensures(Contract.Result<string>().Length <= count); 
     // ReSharper restore PossibleNullReferenceException 

     if (self.Length <= count) 
      return self; 
     else 
      return self.Substring(self.Length - count, count); 
    } 
} 

Answer 3

点点慢于Superbest's solution：

string result = s.Substring(0, Math.Min(s.Length, n));