I'm using a code to save images from a camera, but I need to save the filename with the current date and time the image is taken. How can I do this? I have tried many different codes from the internet but I always get many errors and programming is not my strong side. Any advice or help will be appreciated. This is the code: https://github.com/stereolabs/zed-save-depth/blob/master/src/main.cpp
You can use:
#include <time.h>
for time. To get the current time :
time_t current_time = clock();
To get the current date, you can use :
struct tm *localtime(const time_t *time);
Which returns a struct for the local time that looks like this :
struct tm {
int tm_sec; // seconds of minutes from 0 to 61
int tm_min; // minutes of hour from 0 to 59
int tm_hour; // hours of day from 0 to 24
int tm_mday; // day of month from 1 to 31
int tm_mon; // month of year from 0 to 11
int tm_year; // year since 1900
int tm_wday; // days since sunday
int tm_yday; // days since January 1st
int tm_isdst; // hours of daylight savings time
}
Related
I get week number in ISO 8601 format (%V) using strftime and like to convert to week number shown in my outlook (guess it is gregorian).
Outlook calendar setting is:
First Day of the week (Sunday)
First week of the year starts 1st Jan
For certain years, strftime matches with weeknumber shown in outlook, but for some it doesn't.
A simple code check:
#include <stdio.h>
#include <time.h>
int main ()
{
time_t rawtime;
struct tm *tmDate;
char buffer [80];
time (&rawtime);
tmDate = localtime(&rawtime);
tmDate->tm_hour = 12;
tmDate->tm_mday = 1; //Day of the Month
tmDate->tm_mon = 8; //Month (0=Jan...8=Sep)
tmDate->tm_year = 2018-1900; //Year
mktime(tmDate);
strftime (buffer,80,"%Y-W%V",tmDate);
puts (buffer);
return 0;
}
For above code with it's input, the output will be 2018-W35, which matches with my outlook calendar(https://www.calendar-365.com/2018-calendar.html).
Whereas, if you change year to 2019, the output will be 2019-W35, but in my outlook it falls on 2019-W36 (https://www.calendar-365.com/2019-calendar.html).
Is it possible to map ISO8601 week number to gregorian style?
Any suggestions or code sample will be helpful!
Thank you!
The website you reference seems to use a very unique week numbering system. Its definition of week number appears to mirror the ISO definition with the exception that the first day of the week is Sunday instead of Monday. This means that the first day of the year is the Sunday prior to the first Thursday of the year.
There is no strftime flag to give a week number with this definition. But you can easily compute it with the C++20 <chrono> tools. Unfortunately they aren't shipping yet, but you can use this free, open-source C++20 chrono preview library which works with C++11/14/17.
In addition to computing week number, you'll also need to compute the year, as sometimes the gregorian year does not match the year associated with the week. For example according to https://www.calendar-365.com/2019-calendar.html, December 31, 2018 falls on week 1 of 2019.
So here is a function that computes both the year and the week number, given a date:
#include "date/date.h"
#include <chrono>
#include <iostream>
#include <utility>
// {year, week number}
std::pair<int, int>
outlook_weeknum(date::sys_days sd)
{
using namespace date;
auto y = year_month_day{sd + (Thursday - Sunday)}.year();
auto year_start = sys_days{Thursday[1]/January/y} - (Thursday - Sunday);
if (sd < year_start)
{
--y;
year_start = sys_days{Thursday[1]/January/y} - (Thursday - Sunday);
}
return {int{y}, (sd - year_start)/weeks{1} + 1};
}
The logic is a little tricky. The hard part is finding the first day of the year of the date, which is the Sunday prior to the first Thursday of the year. This is nominally:
auto year_start = sys_days{Thursday[1]/January/y} - (Thursday - Sunday);
where y is the year in the week numbering system (usually, but not always the same as the gregorian year). When the date is very late in the year i.e. December 28 - 31, it may fall in the first week of the next year. To catch that possibility, first bump the date by 4 days (the difference between Sunday and Thursday), and then compute the current year.
S M T W T F S
y-1 WL 21 22 23 24 25 26 27
y W1 28 29 30 31 1 2 3
After doing this, compute the start of the year. And if the start of the year happens to be after the date, then you are in the situation that your date belongs in the previous year. In this case, the week number year may be one less than the gregorian year. This can happen when Jan 1 is Friday or Saturday.
S M T W T F S
y-1 WL 27 28 29 30 31 1 2
y W1 3 4 5 6 7 8 9
In summary, the dates 12/28 - 12/31 can have a week year number either equal to their gregorian year, or one greater. And the dates 01/01 and 01/02 can have a week year number either equal to their gregorian year, or one lesser. -- All depending on what day of the month the first Thursday of January falls on [1 - 7].
Once the week number year (y) is figured out, then the week number is simply the difference between the date and the first of the year divided by 7 days (1 week), plus one to bias the first week to 1 instead of 0.
This can be exercised like this:
int
main()
{
using namespace date;
auto [i, w] = outlook_weeknum(2019_y/9/1);
std::cout << i << "-W" << w << '\n';
}
which outputs:
2019-W36
To port this code to C++20:
Drop the #include "date/date.h"
Change namespace date to namespace std::chrono
Change 2019_y to 2019y
I am trying to get Week of Year. For this I am using tm * __CRTDECL localtime(const time_t * _Time) but I am not getting desired result which should be locale dependent. So I was looking for solution and some more information. I have found that there is API in JAVA Calendar.getInstance(Locale.GERMAN);.So I am just wondering whether there is such API in c/c++ as I did not find any ( not sure ). If not can anybody give me some time pointers to get Week of Year locale dependant.
The code I am using
int MyClass::getCalendarWeek(time_t time, int * p_year)
{
// Get tm structure of time parameter
tm* pCurrentTm = localtime(&time);
// determine Thursday in that week
LONG offSet = 4 - pCurrentTm->tm_wday;
if (offSet >= 4) {
offSet = -3; // Sunday
}
time += offSet * 86400L;
pCurrentTm = localtime(&time);
if (p_year) {
*p_year = pCurrentTm->tm_year + 1900;// year of current calendar week
}
return (pCurrentTm->tm_yday + 7) / 7; // current calendar week
}
Output:
11 July is in week 28 when running most locales that have monday as first day of the week, but it is week 29 for sunday as first day of week.
I am trying to write an application for an assignment and I am new to c++. A small portion of the application requires me to store a date and add an arbitrary number of days as an offset from the date. I know how I would accomplish this with Java or C# but I have been unable to find anything for c++. My professor alluded to ctime but after many searches all the examples I found had to do with the current system time. How do I create a ctime::tm struct and set it to an arbitrary date? Is it possible to add a number of days using ctime to obtain another date? For example, if I added 40 days to January 1, 2001 I would expect February 10, 2001 not January 41, 2001.
To be an example of usage
#include <stdio.h>
#include <time.h>
int main ()
{
time_t currentTime;
time(¤tTime);
struct tm * tmDate;
int day, month, year;
tmDate = localtime (¤tTime);
tmDate->tm_year = 99;
tmDate->tm_mon = 11;
tmDate->tm_mday = 10;
mktime ( tmDate );
printf("now: %d-%d-%d %d:%d:%d\n", tmDate->tm_year + 1900, tmDate->tm_mon + 1, tmDate->tm_mday, tmDate->tm_hour, tmDate->tm_min, tmDate->tm_sec);
return 0;
}
as you can see on
tmDate->tm_year = 99;
tmDate->tm_mon = 11;
tmDate->tm_mday = 10;
you can set, sub, add months, years, days .. to date.
For example simply you can add 1 month to date with
tmDate->tm_mon++;
I know the Current system time.
I know the estimated time of arrival of a place in the form of hours minutes and seconds.
I need to find the duration of travel. But the estimated time of arrival is in 12 hour format.
I have to write a program to find the time difference between these two ?
I thought of using difftime(time1,time2)
but this requires the datatype time_t. I know the time in parts. i.e. i know the hours, minutes and seconds separatley. Both current system time and Estimated time of arrival.
I need to find the time difference between the two. The ETA can be after 24 hours. then is there any way i can find out the number of days of travel. Because after 12PM time is set back. hence i'm not able to keep track of the days.
Any solution ?
I work on C++
A straight forward way using C/C++. This is not very robust, but should meet your given requirements.
#include <ctime>
tm source;
memset(&source, 0, sizeof(tm));
tm.tm_hour = hour; // 24 hour format, 0 = midnight, 23 = 11pm
tm.tm_min = min;
tm.tm_sec = sec;
tm.tm_mon = month; // 0 based, 0 = jan, 11 = dec
tm.tm_mday = 10;
tm.tm.year = year; // current - 1900
time_t src_t = mktime(&source);
time_t now = time(NULL);
Continuing on my attempt to create a DateTime class , I am trying to store the "epoch" time in my function:
void DateTime::processComponents(int month, int day, int year,
int hour, int minute, int second) {
struct tm time;
time.tm_hour = hour;
time.tm_min = minute;
time.tm_sec = second;
time.tm_mday = day;
time.tm_mon = month;
time.tm_year = year - 1900;
ticks_ = mktime(&time);
processTm(time);
}
void DateTime::processTm(struct tm time) {
second_ = time.tm_sec;
minute_ = time.tm_min;
hour_ = time.tm_hour;
weekday_ = time.tm_wday;
monthday_ = time.tm_mday;
yearday_ = time.tm_yday;
month_ = time.tm_mon;
year_ = time.tm_year + 1900;
}
For an arbitrary date, processComponents(5,5,1990,1,23,45) (June 6, 1990 1:23:45 am), it sets all values correctly and as expected.
However, upon further testing, I find that for processComponents(0,0,1970,0,0,0) (January 1, 1970, 12:00:00 am), mktime(&time) causes time to be screwed up:
time.tm_mon = 11;
time.tm_mday = 30;
time.tm_year = 69;
time.tm_hour = 23;
time.tm_min = 0;
time.tm_sec = 0;
time.tm_isdst = 0;
time.tm_gmtoff = -18000;
time.tm_zone = "EST";
time.tm_wday = 2;
time.tm_yday = 363;
Translating to a date of December 31, 1969 11:00:00 pm.
I can verify that mktime() is responsible, because by commenting out that line, it reports the date and time correctly as January 1, 1970 12:00:00 am.
Why is mktime() only messing up the epoch? And how should I fix / workaround this?
Thanks!
You're passing 0 as the day parameter and putting that into time.tm_mday. That component (and only that component) of struct tm is 1-based, not 0-based.
Don't ask me why.
To specify 01 Jan 1970, 12:00:00am you'd want to call it like so:
processComponents(0,1,1970,0,0,0);
And as sdtom mentioned, you'll want to make sure that tm_isdst is set appropriately - 0 for not in effect, positive for in effect, and negative for you don't know (in which case mktime() should try to guess).
Just to let you know, when I pass the date you have (0 Jan 1970, 00:00:00) to mktime() in MSVC 9 it returns an error (the passed in struct tm is untouched and the returned time_t value is -1).
Since it is off by one hour I would expect daylight savings time. Is the value of time.tm_isdst getting set somewhere? If you aren't setting it, it could be randomly getting set to 1 or 0 which would affect your results.
Passing all zeros to mktime() is interpreted as "Sun Jan 0 00:00:00 1900". Based on this, there needs to be some adjustments...
// the input is local time
// the output is seconds since the epoch
// The epoch is Jan 1, 1970 # 0:00 GMT
time_t mktime_wrapper( int month, int day, int year,
int hour=0, int min=0, int sec=0, bool isDST=-1
)
{
tm t;
t.tm_sec=sec, t.tm_min=min, t.tm_hour=hour, t.tm_isdst=isDST;
t.tm_mday=day, t.tm_mon=month-1, t.tm_year=year-1900;
return mktime( &t );
}