QT程序中QDateTime转化为字符串的格式问题

在QT程序中获取系统时间是非常方便的，例如：

    QDateTime localTime(QDateTime::currentDateTimeUtc().toLocalTime());

    img.save("save/"+localTime.toString("yyyyMMddhhmmss")+".jpg");

其中toString函数参数可根据显示需求自行确定，具体参数格式如下：

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".

除以上专用字符串以外，其它字符都会按照用户编辑原样显示。