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    <p>Maybe you should look at the <a href="http://www.boost.org/doc/libs/1_39_0/doc/html/date_time/gregorian.html" rel="nofollow">boost::date_time::gregorian</a>. Using it you can write a function like that:</p> <pre><code>#include &lt;boost/date_time/gregorian/gregorian.hpp&gt; // Get the date for a given year, week and weekday(0-6) time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek) { using namespace boost::gregorian; date d(year, Jan, 1); int curWeekDay = d.day_of_week(); d += date_duration((week - 1) * 7) + date_duration(dayOfWeek - curWeekDay); tm tmp = to_tm(d); time_t * ret = new time_t(mktime(&amp;tmp)); return ret; } </code></pre> <p>Unfortunately their format of date is different from yours - they numerate days of week starting from Sunday, i.e. <code>Sunday = 0, Monday = 1, ..., Saturday = 6</code>. If it doesn't satisfy your needs, you can use this slightly changed function:</p> <pre><code>#include &lt;boost/date_time/gregorian/gregorian.hpp&gt; // Get the date for a given year, week and weekday(1-7) time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek) { using namespace boost::gregorian; date d(year, Jan, 1); if(dayOfWeek == 7) { dayOfWeek = 0; week++; } int curWeekDay = d.day_of_week(); d += date_duration((week - 1) * 7) + date_duration(dayOfWeek - curWeekDay); tm tmp = to_tm(d); time_t * ret = new time_t(mktime(&amp;tmp)); return ret; } </code></pre> <p><strong>EDIT:</strong></p> <p>After thinking a little I found a way to implement the same function without using boost. Here is the code:</p> <p><strong>WARNING: the code below is broken, do not use it!</strong></p> <pre><code>// Get the date for a given year, week and weekday(1-7) time_t *GetDateFromWeekNumber(int year, int week, int dayOfWeek) { const time_t SEC_PER_DAY = 60*60*24; if(week_day == 7) { week_day = 0; week++; } struct tm timeinfo; memset(&amp;timeinfo, 0, sizeof(tm)); timeinfo.tm_year = year - 1900; timeinfo.tm_mon = 0; timeinfo.tm_mday = 1; time_t * ret = new time_t(mktime(&amp;timeinfo)); // set all the other fields int cur_week_day = timeinfo.tm_wday; *ret += sec_per_day * ((week_day - cur_week_day) + (week - 1) * 7); return ret; } </code></pre> <p><strong>EDIT2:</strong></p> <p>Yep, code in <strong>EDIT</strong> is completely broken because I didn't take enough time to understand how week numbers are assigned.</p>
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    1. POCalculate Gregorian date from week number in C/C++
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    1. USMikhail Melnik
    1. USMikhail Melnik
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    1. COThanks, but we are not using Boost.
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    2. COWhen it comes to your non-Boost example then it returns the _18th of December 2005_ when year is 2005, week is 52 and weekday is 1, when the correct answer should have been _26th of December 2005_ , see http://www.epochconverter.com/date-and-time/weeknumbers-by-year.php?year=2005 . I have fixed my own algorithm now (see my answer) but I thought you would like to know that your code is broken.
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