converting milliseconds to date in C

Question

Is there any way of converting milliseconds to date in C?

What I am trying to do is write a small application in C that can return the financial year and the like(quarter, week) given the start month and isCurentYear bool, where the input might be milliseconds or a date!

In the first place, is there any way by which this can be achieved in C?

And if so, in the process of finding out a way of converting milliseconds to date I have found out that the use of time_t takes the current millis of our system and by creating a structure pointing to it,it permits us to extract the year,month, date, sec etc!

Refer the below code:

#include <sys/time.h>
#include<stdio.h>
#include<time.h>

void main()
{
    time_t t = time(000);
    //time_t t = time(0);
    struct tm tm = *localtime(&t);

    printf("now: %d-%d-%d %d:%d:%d\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
                                       tm.tm_hour, tm.tm_min, tm.tm_sec);
}

And also, can time_t be used to store millisecond values so that it can be converted to date using tm struct?

Answer 1

Function time_t time(time_t* timer) returns the number of seconds elapsed since 00:00 hours, Jan 1, 1970 UTC. In addition, if the input argument timer != NULL, then the function also sets this argument to the same value (so you probably have no reason to call it with anything else but NULL).

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Function struct tm* localtime(const time_t* timer) takes the number of seconds elapsed since 00:00 hours, Jan 1, 1970 UTC, and returns a structure that represents the equivalent time & date. If you're working on a multi-threaded application, then please note that this function is not thread safe.

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As to your question - is there any way for converting milliseconds to time & date - yes, but:

• Take into consideration that the milliseconds will be considered as of 00:00 hours, Jan 1, 1970 UTC.
• Since the time_t type is 32-bit long, you will not be able to convert 4G*1000 milliseconds or more.

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Here is a function for converting milliseconds to time & date:

struct tm* GetTimeAndDate(unsigned long long milliseconds)
{
    time_t seconds = (time_t)(milliseconds/1000);
    if ((unsigned long long)seconds*1000 == milliseconds)
        return localtime(&seconds);
    return NULL; // milliseconds >= 4G*1000
}