Parsing dates with no separating marks.

[wiluite]

Hello,

Can one use the date library for parsing dates/datetimes (at least, dates) represented by such a non-standard format like "yyyymmdd", i.e without separating marks?

Thanks.

[HowardHinnant]

Yes:

#include "date/date.h"
#include <chrono>
#include <iostream>
#include <sstream>

int
main()
{
    using namespace date;
    using namespace std;
    using namespace chrono;

    istringstream in{"20241126"};
    sys_days tp;
    in >> parse("%Y%m%d", tp);
    cout << tp << '\n';
}

Output:

2024-11-26

Several of the flags have default widths, beyond which no parsing will take place. For example the default width for %Y is 4. There is also a way to modify the default width, for example %2Y will only read two digits for the year. But that year will become a year in the first century, not a recent year.

Here are the details: https://howardhinnant.github.io/date/date.html#from_stream_formatting

This library is also now part of C++20, but in namespace std::chrono and in header <chrono>. If you can use C++20 and your vendor implements it, I encourage the use of the <chrono> version over this library.