How to get the date and time values in a C program?

To expand on the answer by Ori Osherov

You can use the WinAPI to get the date and time, this method is specific to Windows, but if you are targeting Windows only, or are already using the WinAPI then this is definitly a possibility¹:

You can get both the time and date by using the SYSTEMTIME struct. You also need to call one of two functions (either GetLocalTime() or GetSystemTime()) to fill out the struct.

GetLocalTime() will give you the time and date specific to your time zone.

GetSystemTime() will give you the time and date in UTC.

The SYSTEMTIME struct has the following members:

wYear, wMonth, wDayOfWeek, wDay, wHour, wMinute, wSecond and wMilliseconds

You then need to just access the struct in the regular way

Actual example code:

#include <windows.h> // use to define SYSTEMTIME , GetLocalTime() and GetSystemTime()
#include <stdio.h> // For printf() (could otherwise use WinAPI equivalent)

int main(void) { // Or any other WinAPI entry point (e.g. WinMain/wmain)

    SYSTEMTIME t; // Declare SYSTEMTIME struct

    GetLocalTime(&t); // Fill out the struct so that it can be used

    // Use GetSystemTime(&t) to get UTC time 

    printf("Year: %d, Month: %d, Day: %d, Hour: %d, Minute:%d, Second: %d, Millisecond: %d", t.wYear, t.wMonth, t.wDay, t.wHour, t.wMinute, t.wSecond, t.wMilliseconds); // Return year, month, day, hour, minute, second and millisecond in that order

    return 0;
}

(Coded for simplicity and clarity, see the original answer for a better formatted method)

The output will be something like this:

Year: 2018, Month: 11, Day: 24, Hour: 12, Minute:28, Second: 1, Millisecond: 572

Useful References:

All the WinAPI documentation (most already listed above):

• GetLocalTime()
• GetSystemTime()
• SYSTEMTIME
• Time Functions

An extremely good beginners tutorial on this subject by ZetCode:

• https://zetcode.com/gui/winapi/datetime/

Simple operations with datetime on Codeproject:

• https://www.codeproject.com/Articles/5546/WinAPI-Simple-Operations-with-datetime

1: As mentioned in the comments in Ori Osherov's answer ("Given that OP started with date +%F, they're almost certainly not using Windows. – melpomene Sep 9 at 22:17") the OP is not using Windows, however since this question has no platform specific tag (nor does it mention anywhere that the answer should be for that particular system), and is one of the top results when Googling "get time in c" both answers belong here, some users searching for an answer to this question may be on Windows and therefore will be useful to them.

Timespec has day of year built in.

http://pubs.opengroup.org/onlinepubs/7908799/xsh/time.h.html

#include <time.h>
int get_day_of_year(){
    time_t t = time(NULL);
    struct tm tm = *localtime(&t);
    return tm.tm_yday;
}`

I was using command line C-compiler to compile these and it completely drove me bonkers as it refused to compile.

For some reason my compiler hated that I was declaring and using the function all in one line.

struct tm tm = *localtime(&t);

test.c
test.c(494) : error C2143: syntax error : missing ';' before 'type'
Compiler Status: 512

First declare your variable and then call the function. This is how I did it.

char   todayDateStr[100];
time_t rawtime;
struct tm *timeinfo;

time ( &rawtime );
timeinfo = localtime ( &rawtime );
strftime(todayDateStr, strlen("DD-MMM-YYYY HH:MM")+1,"%d-%b-%Y %H:%M",timeinfo);
printf("todayDateStr = %s ... \n", todayDateStr );

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

struct date
{
    int month;
    int day;
    int year;
};

int calcN(struct date d)
{
    int N;
    int f(struct date d);
    int g(int m);

    N = 1461 * f(d) / 4 + 153 * g(d.month) / 5 + d.day;

    if(d.year < 1700 || (d.year == 1700 && d.month < 3))
    {
        printf("Date must be after February 29th, 1700\n");

        return 0;
    }
    else if(d.year < 1800 || (d.year == 1800 && d.month < 3))
        N += 2;
    else if(d.year < 1900 || (d.year == 1900 && d.month < 3))
        N += 1;    

    return N;
}

int f(struct date d)
{
    if(d.month <= 2)
        d.year -= 1;

    return d.year;
}

int g(int m)
{
    if(m <=2)
        m += 13;
    else
        m += 1;
    
    return m;
}

int main(void)
{
    int calcN(struct date d);
    struct date d1, d2;
    int N1, N2;
    time_t t;

    time(&t);
    struct tm *now = localtime(&t);


    d1.month = now->tm_mon + 1;
    d1.day = now->tm_mday;
    d1.year = now->tm_year + 1900;

    printf("Today's date: %02i/%02i/%i\n", d1.month, d1.day, d1.year);

    N1 = calcN(d1);

    printf("Enter birthday (mm dd yyyy): ");
    scanf("%i%i%i", &d2.month, &d2.day, &d2.year);

    N2 = calcN(d2);

    if(N2 == 0)
        return 0;

    printf("Number of days since birthday: %i\n", N1 - N2);

    return 0;
}

#include <stdio.h>

int main() {
    char *pts; /* pointer to time string */
    time_t now; /* current time */
    char *ctime();
    (void) time(&now);
    printf("%s", ctime(&now));

   return(0);
}

Sample output:

Sat May 14 19:24:54 2022

This is the easiest way. I haven't even used time.h.

Be advised: The output produced has a newline at the end.