比较c ++中的2个日期 [英] Comparing 2 dates in c++
问题描述
我想知道在C ++中是否有相对简单和简短的日期比较函数。
我的日期类型为 char *
,格式如下: DD\MM\YYYY
I was wondering if there is any relatively easy and short date comparison functions in C++.
My dates are of type char*
, and have the following format: DD\MM\YYYY
谢谢。
推荐答案
解析通常是在流,不是字符串,但可以使用 stringstream
。
Parsing is usually done on streams, not strings, but you can use a stringstream
.
std::istringstream date_s( "04\\10\\1984" );
struct tm date_c;
date_s >> std::get_time( &date_c, "%d\\%m\\%Y" );
std::time_t seconds = std::mktime( & date_c );
现在您可以使用<
请注意, std :: get_time
是C ++ 11中的新增功能。它是根据 strptime
定义的,它来自POSIX,但不是C99标准的一部分。您可以使用 strptime
如果C ++ 11库不可用。如果你勇敢,你也可以使用 std :: time_get
facet ...它很丑陋。
Note, std::get_time
is new in C++11. It is defined in terms of strptime
, which is from POSIX but not part of the C99 standard. You can use strptime
if a C++11 library is not available. If you're brave, you can also use the std::time_get
facet… it's ugly though.
你不想知道除了早先的日期之外的任何事情,你可以使用 std :: lexicographical_compare
。
If you don't want to know anything about the dates other than which is earlier, you can use std::lexicographical_compare
. It would be a one-liner but the function name is so long.
// return true if the date string at lhs is earlier than rhs
bool date_less_ddmmyyyy( char const *lhs, char const *rhs ) {
// compare year
if ( std::lexicographical_compare( lhs + 6, lhs + 10, rhs + 6, rhs + 10 ) )
return true;
if ( ! std::equal( lhs + 6, lhs + 10, rhs + 6 ) )
return false;
// if years equal, compare month
if ( std::lexicographical_compare( lhs + 3, lhs + 5, rhs + 3, rhs + 5 ) )
return true;
if ( ! std::equal( lhs + 3, lhs + 5, rhs + 3 ) )
return false;
// if months equal, compare days
return std::lexicographical_compare( lhs, lhs + 2, rhs );
}
另请参阅如何在c?中将datetime转换为unix时间戳。
See also how to convert datetime to unix timestamp in c? .
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