比较C ++中的两个时间戳字符串

Question

I have two timestamps stored as string variables. The timestamps are in the format dd/mm/yyyy-hh:mm:ss I am trying to find the difference in seconds between the two timestamps (ignoring the dates).

(I haven't assigned strings to a and b but they hold a timestamp each)

It always outputs 0 for the number of seconds difference and I can't work out why.

std::string a, b; // hold timestamps
struct tm t, t1;
double seconds;

t.tm_hour = stoi(a.substr(11,2)); // stoi() cast substring to int
t.tm_min = stoi(a.substr(14,2));
t.tm_sec = stoi(a.substr(17,2));

t1.tm_hour = stoi(b.substr(11,2));
t1.tm_min = stoi(b.substr(14,2));
t1.tm_sec = stoi(b.substr(17,2));

seconds = difftime(mktime(&t1), mktime(&t));
std::cout<<seconds;

Answer 1

Don't use hardcoded substring values (1 minute vs 11 minute might make you go off if 01 notation isn't used... and you have months ,days and hours also to take into account).

Instead of hardcoding the offset try to go after the unique characters (for you to get the "seconds" , take account the only the string after the 2nd occurrence of ":" ).

Answer 2

I suggest use CTime to work with timestamp.

http://www.cplusplus.com/reference/ctime/

You can use this for storage and later, if you need, convert to string.

Answer 3

This would be a great reason to start with the Boost libraries, because Boost.Date_Time has exactly what you need. See the documentation about time durations .

Here is an example program:

#include <boost/date_time/posix_time/posix_time.hpp>
#include <iostream>

int main()
{
    boost::posix_time::time_duration duration1 = boost::posix_time::duration_from_string("10:11:12");
    boost::posix_time::time_duration duration2 = boost::posix_time::duration_from_string("10:12:15");

    std::cout << (duration2 - duration1).total_seconds() << "\n";
}

Output: 63

Since you are already using substr and std::stoi , it should be easy for you to get the proper substrings from a and b to be passed to boost::posix_time::duration_from_string .

Answer 4

Add following code after the defintions and before the assignments

// initialize time structures with all the details for 'now'
time_t ts;
time( &ts );
t = * localtime( &ts );
t1 = t;