当我给strftime无效的说明符时会发生什么？

Question

我尝试提供strftime不在列表中的修饰符％k，并且打印11，当我提供不在列表中的修饰符时，strftime会做什么？

Answer 1

From the C standard of strftime :

6 If a conversion specifier is not one of the above, the behavior is undefined.

You can see the list of format specifiers for strftime. So what you are getting is an undefined behavior .

See the manual which says about %k

%k The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank. (See also %H.) (TZ)

Answer 2

%k - The hour as a decimal number, using a 24-hour clock like %H , but padded with blank (range 0 through 23).

But this format is a GNU extension. See here listed specifiers .

And if the specifier not listed is used code will exbhit undefined behaviour .