c# - 在 .NET 中使用字符串格式 "M"发出 DateTime.ToString

Question

我对 DateTime 的字符串格式有疑问。我认为这是 MS 中的错误。你能解释一下吗？有什么问题吗？

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(DateTime.Now.ToString("M"));//return 07 July   <---- WRONG, SEE MSDN
        Console.WriteLine(DateTime.Now.ToString(".M"));//return .7   <---- GOOD
        Console.ReadKey();
    }
}

MSDN

Answer 1

来自 The "M" Custom Format Specifier

If the "M" format specifier is used without other custom format specifiers, it is interpreted as the "M" standard date and time format specifier. For more information about using a single format specifier, see Using Single Custom Format Specifiers later in this topic.

来自 Using Single Custom Format Specifiers

A custom date and time format string consists of two or more characters. Date and time formatting methods interpret any single-character string as a standard date and time format string. If they do not recognize the character as a valid format specifier, they throw a FormatException. For example, a format string that consists only of the specifier "h" is interpreted as a standard date and time format string. However, in this particular case, an exception is thrown because there is no "h" standard date and time format specifier.

To use any of the custom date and time format specifiers as the only specifier in a format string (that is, to use the "d", "f", "F", "g", "h", "H", "K", "m", "M", "s", "t", "y", "z", ":", or "/" custom format specifier by itself), include a space before or after the specifier, or include a percent ("%") format specifier before the single custom date and time specifier.

这就是您可以使用其中之一的原因；

Console.WriteLine(DateTime.Now.ToString(" M")); // 7
Console.WriteLine(DateTime.Now.ToString("M ")); //7
Console.WriteLine(DateTime.Now.ToString("%M")); //7