Does following DateTime format "%M/%d/yyyy %H:%m:%s" will include both lines, e.g. with or without leading zero:
Line 1: 4/8/2022 7:6:3 Line 2: 04/08/2022 07:06:03
It's seems to be working but related documentation is more welcome.
CodePudding user response：
The related documentation can be found here: https://docs.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings
Note the description of the % symbol: "Defines the following character as a custom format specifier".[1]
Since you have a custom date time format string, the symbols M, d, H, ... are custom format specifiers. This means, here % essentially becomes a no-operation without any effect, because the symbols following it are already custom format specifiers.
So, what exactly is the purpose of % if the symbols in a custom date time format string are already custom format specifiers regardless of % being there or not? The reason for % becomes understandable when you consider that there are also standard date time format strings, which consist of a single character, a single format specifier. Pertinent documentation here: https://docs.microsoft.com/en-us/dotnet/standard/base-types/standard-date-and-time-format-strings
Basically, any date time format string made of only one character is treated as a standard date time format string. And any date time format string with two or more characters is treated as a custom date time format string.
What if you want to use a custom date time format string consisting of only one custom format specifier? That one-character string will be interpreted as a standard date time format string instead. And that is a problem.
If you compare the lists of specifiers for standard and custom date time format strings, you'll notice that many of the standard date time format specifiers use symbols that are also used by custom date time format specifiers. However, standard date time format specifiers represent different data and/or formatting patterns than the respective custom date time format specifier using the same symbol. For example, the standard date time format specifier y yields year month, while the custom date time format specifier y yields the last two digits of the year.
Therefore, if you need a functionally single-specifier custom date time format string, you gotta fatten up that string and turn it from a one-character string into a two-characters string with the help of the "no-op" specifier %, so that it will be correctly treated as a custom date time format string.
As an example, imagine you want to get just the last two digits of the year and nothing more, and you decide to use the custom format specifier y which does exactly what you want. However, the format string "y" is a standard date time format string yielding year month. So, how do you get what you want? You turn the standard date time format string "y" into a custom date time format string by using "%y".
[1]According to that documentation, it should theoretically be possible to use contiguous sequences of multiple % in custom date time format string like "%%%%%M/%%%%%%d". Each of those % sequences should functionally collapse into a single %, as by definition according to the quoted documentation, each % defines the following % as a custom format specifier that it already is. However -- and for the better, i might add -- the DateTime formatting functions will have none of such shenanigans and throw a FormatException for you being a bad boy having even tried this...