日期/时间的存储与解析

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November 04

日期/时间的存储与解析

最近做的项目中有这样一个需求:将一个uint32的整数解析到一个结构体中去.

uint32整数的"组装"方式为:

time = (CLFS_time_t)(FileCreationHour << 11) | (CLFS_time_t)(FileCreationMinute << 5) | (CLFS_time_t)(FileCreationSecond);
data = (CLFS_time_t)((FileCreationYear - 1980) << 9) | (CLFS_time_t)(FileCreationMonth << 5) | (CLFS_time_t)(FileCreationDay);
uint32st_ctime = (data << 16) | (time & 0xFFFF);

用图片表示的话就是:

(1090 * 83的图片so小...)

结构体为:

typedef struct
{
uint16 year; /* Year [1980..2100] */
uint16 month; /* Month of year [1..12] */

uint16 day; /* Day of month [1..31] */

uint16 hour; /* Hour of day [0..23] */

uint16 minute; /* Minute of hour [0..59] */

uint16 second; /* Second of minute [0..59] */

uint16 day_of_week; /* Day of the week [0..6] [Monday .. Sunday] */
}time_julian_type;

很明显,如果我想解析上面的uint32到下面的结构体中去,必须做与"组装"相反的工作:先解析出16bits 的data = uint32st_ctime >> 16,则year = data >> 9,month = (data >> 5) & 0xF,day = data & (1 << 6 -1),time与此类似.

可以看出,上面的步骤手工计算的地方比较多,所以容易出错,而且复查起来也比较耗时间.那么,我们采取另外一种办法,直接把每个item的bit数列出来,这样比较直观,而且不会出错.

typedef struct time_struct_type
{
uint16 year : 7;
uint16 month : 4;
uint16 day : 5;
uint16 hour : 5;
uint16 minute : 6;
uint16 second : 5;
}time_struct_t;

这个结构体用到了bitset,一目了然.好,直接把uint32的值赋给它:*((uint32 *)&time_struct) = uint32st_ctime;

OK,现在就可以把time_struct里的各项内容直接赋给time_julian_type结构体啦,任务完成 :)

3:24 PM | Blog it

Comments (2)

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zw shaowrote:

俺来踢个馆:)

uint16 second : 5；只能表示 [0..31]
我想博主当时也为这个稍微伤了一下神，本来是要写成uint16 second : 6的，不得已削足适履了。大概博主的程序对时间的要求并不需要精确到秒吧。
这个方法能凑效应该说是相当的巧合(当然也巧妙！)，假如你的程序需要处理的时间跨度超过128年的话(顺祝博主的程序能够流芳千古^_^)，那么year这个脚趾头就足够难缠了，即便只增长1个bit，改成uint16 year : 8，呵呵，博主可以试试看，继续再砍掉脚后跟second 1个bit也还是穿不下32bit的鞋，bit field的脾气是出了名的古怪，非不得已咱都是敬而远之哦。

3 days ago

Ericwrote:

这个bitset一般用在什么地方?

Mar. 24

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