1.主要类：QDateTime
2.获取日期：QDateTime time=QDateTime::currentDateTime();
3.从时间中提取指定格式的字符串：QString strDate=time.toString("yyyy");
4.格式字符串：
QString QDateTime::toString ( const QString & format ) const
Returns the datetime as a string. The format parameter determines the format of the result string.
These expressions may be used for the date:
Expression Output
d the day as number without a leading zero (1 to 31)
dd the day as number with a leading zero (01 to 31)
ddd the abbreviated localized day name (e.g. 'Mon' to 'Sun'). Uses QDate::shortDayName().
dddd the long localized day name (e.g. 'Monday' to 'Qt::Sunday'). Uses QDate::longDayName().
M the month as number without a leading zero (1-12)
MM the month as number with a leading zero (01-12)
MMM the abbreviated localized month name (e.g. 'Jan' to 'Dec'). Uses QDate::shortMonthName().
MMMM the long localized month name (e.g. 'January' to 'December'). Uses QDate::longMonthName().
yy the year as two digit number (00-99)
yyyy the year as four digit number
These expressions may be used for the time:
Expression Output
h the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)
hh the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)
m the minute without a leading zero (0 to 59)
mm the minute with a leading zero (00 to 59)
s the second without a leading zero (0 to 59)
ss the second with a leading zero (00 to 59)
z the milliseconds without leading zeroes (0 to 999)
zzz the milliseconds with leading zeroes (000 to 999)
AP use AM/PM display. AP will be replaced by either "AM" or "PM".
ap use am/pm display. ap will be replaced by either "am" or "pm".
All other input characters will be ignored. Any sequence of characters that are enclosed in singlequotes will be treated as text and not be used as an expression. Two consecutive singlequotes ("''") are replaced by a singlequote in the output.
Example format strings (assumed that the QDateTime is 21 May 2001 14:13:09):
Format Result
dd.MM.yyyy 21.05.2001
ddd MMMM d yy Tue May 21 01
hh:mm:ss.zzz 14:13:09.042
h:m:s ap 2:13:9 pm