C 語言 日期與時間的運算及格式化
作者：許裕永 Darban
日期與時間的運算及格式化是程式語言必學的項目之一，在 C 語言中運算與格式化時間及日期的函式由標頭檔 time.h提供。
因為在這裡的函式呼叫，無論參數列或返回值均大量的使用指標，沒學過指標的同學請先參閱指標相關章節。
*_* 取得現在時間
函式：time_t time (time_t* timer);
取得自 1970 年 1 月 1 日 00:00 到現在的秒數。在程式中直接使用這個值並不適當。一般而言會使用
stdio.h 中的函式，將它格式化之後再輸出。
型別： time_t
time_t 型別是一個不屬於基本型別的整數擴充型別，用來儲存秒數，只用於時間運算。
參數：time_t*
一個 time_t 型別的指標，運算後會產生一個 time_t 型別的值，儲存此值的記憶體空間的記憶體位址將會被儲存在指標參數之中。
另外，這個參數的值可以是 null ，在這種狀況這個參數將不會被使用，但這個函式仍然會運出 time_t 型別的值並將其做為返回值
返回值
包含目前時間的 time_t 型別的值。.
範例一：
將 time() 的返回值指派給宣告 time_t 變數。
int main(int argc, char *argv[]) {
time_t now =
time(NULL);
printf("%d",now);
return 0;
}
範例二：
宣告指標做為 time() 的參數。
int main(int argc, char *argv[]) {
time_t* now;
time(now);
printf("%d",*now);
return 0;
}
*_* 格式化 time_t 的值
函式：char* ctime (const time_t *
timer);
範例：
int main(int argc, char *argv[]) {
time_t* now;
time(now);
printf("The date
and time is : %s", ctime(now));
return 0;
}
*_* 區域化 time_t 的值
函式：struct tm * localtime (const
time_t * timer);
把 time_t 物件轉成區域化之後的 tm 型別物件。
型別： struct tm
這個結構包含了九種 int 型別的成員：
|
Member
|
Type
|
Meaning
|
Range
|
|
tm_sec
|
int
|
seconds after the minute
|
0-61
|
|
tm_min
|
int
|
minutes after the hour
|
0-59
|
|
tm_hour
|
int
|
hours since
|
0-23
|
|
tm_mday
|
int
|
day of the month
|
1-31
|
|
tm_mon
|
int
|
months since January
|
0-11
|
|
tm_year
|
int
|
years since 1900
|
|
|
tm_wday
|
int
|
days since Sunday
|
0-6
|
|
tm_yday
|
int
|
days since January 1
|
0-365
|
|
tm_isdst
|
int
|
Daylight Saving Time flag
|
|
參數：time_t*
time_t 型別的物件的記憶體位址。
返回值： struct tm*
struct tm 型別的物件的指標。
範例：
int main(int argc, char *argv[]) {
time_t* now;
time(now);
struct tm* localNow =
localtime(now);
printf("%d/%d/%d\n",localNow->tm_year
+ 1900,localNow->tm_mon +1,localNow->tm_mday);
printf("%d:%d:%d\n",localNow->tm_hour,localNow->tm_min,localNow->tm_sec);
return 0;
}
*_* 格式化 struct tm 物件
函式Ａ：char* asctime (const struct tm *
timeptr);
範例：
int main(int argc, char *argv[]) {
time_t* now;
time(now);
struct tm* now_tm
= localtime(now);
printf("The date
and time is : %s", asctime(now_tm));
return 0;
}
函式Ｂ：size_t strftime (char* ptr,
size_t maxsize, const char* format,
const struct
tm* timeptr );
參數：
|) char* ptr
用來儲存格式化後的文字的指標。
|) size_t maxsize
設定文字的最大長度，包含文字終止符號。
|) char* format
使用下列表格代號，指定格式。
|
specifier
|
Replaced by
|
Example
|
|
%a
|
Abbreviated weekday name *
|
Thu
|
|
%A
|
Full weekday name *
|
Thursday
|
|
%b
|
Abbreviated month name *
|
Aug
|
|
%B
|
Full month name *
|
August
|
|
%c
|
Date and time representation *
|
Thu Aug 23
|
|
%C
|
Year divided by 100 and truncated to
integer (00-99)
|
20
|
|
%d
|
Day of the month, zero-padded (01-31)
|
23
|
|
%D
|
Short MM/DD/YY date, equivalent to
%m/%d/%y
|
|
|
%e
|
Day of the month, space-padded ( 1-31)
|
23
|
|
%F
|
Short YYYY-MM-DD date, equivalent to
%Y-%m-%d
|
2001-08-23
|
|
%g
|
Week-based year, last two digits (00-99)
|
01
|
|
%G
|
Week-based year
|
2001
|
|
%h
|
Abbreviated month name * (same as %b)
|
Aug
|
|
%H
|
Hour in 24h format (00-23)
|
14
|
|
%I
|
Hour in 12h format (01-12)
|
02
|
|
%j
|
Day of the year (001-366)
|
235
|
|
%m
|
Month as a decimal number (01-12)
|
08
|
|
%M
|
Minute (00-59)
|
55
|
|
%n
|
New-line character ('\n')
|
|
|
%p
|
AM or PM designation
|
PM
|
|
%r
|
12-hour clock time *
|
|
|
%R
|
24-hour HH:MM time, equivalent to %H:%M
|
|
|
%S
|
Second (00-61)
|
02
|
|
%t
|
Horizontal-tab character ('\t')
|
|
|
%u
|
ISO 8601 weekday as number with Monday as
1 (1-7)
|
4
|
|
%U
|
Week number with the first Sunday as the
first day of week one (00-53)
|
33
|
|
%V
|
ISO 8601 week number (00-53)
|
34
|
|
%w
|
Weekday as a decimal number with Sunday
as 0 (0-6)
|
4
|
|
%W
|
Week number with the first Monday as the
first day of week one (00-53)
|
34
|
|
%x
|
Date representation *
|
|
|
%X
|
Time representation *
|
|
|
%y
|
Year, last two digits (00-99)
|
01
|
|
%Y
|
Year
|
2001
|
|
%%
|
A % sign
|
%
|
參數 struct tm* timeptr
要格式化的 struct tm 物件的記憶體位址。
範例：
int main(int argc, char *argv[]) {
time_t* now;
time(now);
struct tm* now_tm
= localtime(now);
char* date =
(char*)malloc(10);
strftime(date,10,"%x",now_tm);
printf("The date
is : %s\n",date);
char* time =
(char*)malloc(10);
strftime(time,10,"%X",now_tm);
printf("The time
is : %s\n",time);
return 0;
}
*_* 建立指定日期時間的 struct tm 物件
範例一：
int main(int argc, char *argv[]) {
/*
同一個函式中重複呼叫 localtime() 都是在存取同一個 tm 物件。
也就是說，即使每次呼叫都指派給不同的 tm 指標，其實這些指標都指向同一個物件。
所以必須先記錄要運算的值，再修改 tm 欄位中的內容。
*/
//以現在時間建立 tm 物件,填滿其所有欄位
time_t now;
time(&now);
struct tm* birthday =
localtime(&now);
//記錄現在的年
int now_year =
birthday->tm_year + 1900;
//設定指定欄位的值
birthday->tm_year =
1990 - 1900;
birthday->tm_mon = 6
- 1;
birthday->tm_mday =
17;
char* date =
(char*)malloc(10);
strftime(date,10,"%x",birthday);
printf("The
birthday is : %s\n" ,date);
printf("The age is
: %d",now_year- (birthday->tm_year + 1900)) ;
return 0;}
*_* 取得指定日期的tm物件的 time_t 值
函式： time_t mktime (struct tm *
timeptr);
範例：
int main(int argc, char *argv[]) {
time_t seconds;
time(&seconds);
struct tm* day =
localtime(&seconds);
day->tm_year = 2014
- 1900;
day->tm_mon = 3 - 1;
day->tm_mday = 1;
seconds = mktime(day);
seconds += 86400 * 300;
localtime(&seconds);
char* date =
(char*)malloc(10);
strftime(date,10,"%x",day);
printf("The end
day is : %s\n" ,date);
return 0;
}
*_* 取得兩個日期距離的杪數
函數： double difftime (time_t end,
time_t beginning);
範例：
int main(int argc, char *argv[]) {
time_t day = 0;
struct tm* day_tm =
localtime(&day);
day_tm->tm_year =
2012 - 1900;
day_tm->tm_mon = 3 -
1;
day_tm->tm_mday = 5;
time_t startSecond =
mktime(day_tm);
day_tm->tm_year =
2014 - 1900;
day_tm->tm_mon = 5 -
1;
day_tm->tm_mday =
15;
time_t endSecond =
mktime(day_tm);
double seconds =
difftime(endSecond, startSecond);
printf("The days
between start day and end day are : %.0f days",seconds/86400);
return 0;
}
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