Question

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

最简单的方法是什么？

Answer 1

我所知道的最快捷方式是：

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

Answer 2

比Superbest's solution慢一点：

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

Answer 3

最好的方法是编写几种扩展方法。

然后你可以像string result = sourceString.Left(10);

一样使用它

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 4

如果字符串较短或等于所需长度，则只需返回字符串即可。不要仅仅为了返回整个字符串而调用Substring。

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

字符串的前n个字符，即使它比n短？

4 个答案: