I have something like this:
char *current_day, *current_time;
system("date +%F");
system("date +%T");
It prints the current day and time in the stdout, but I want to get this output or assign them to the current_day and current_time variables, so that I can do some processing with those values later on.
current_day ==> current day
current_time ==> current time
The only solution that I can think of now is to direct the output to some file, and then read the file and then assign the values of date and time to current_day and current_time. But I think this is not a good way. Is there any other short and elegant way?
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 );
I'm getting the following error when compiling Adam Rosenfield's code on Windows. It turns out few things are missing from the code.
Error (Before)
C:\C\Codes>gcc time.c -o time
time.c:3:12: error: initializer element is not constant
time_t t = time(NULL);
^
time.c:4:16: error: initializer element is not constant
struct tm tm = *localtime(&t);
^
time.c:6:8: error: expected declaration specifiers or '...' before string constant
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);
^
time.c:6:36: error: expected declaration specifiers or '...' before 'tm'
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);
^
time.c:6:55: error: expected declaration specifiers or '...' before 'tm'
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);
^
time.c:6:70: error: expected declaration specifiers or '...' before 'tm'
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);
^
time.c:6:82: error: expected declaration specifiers or '...' before 'tm'
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);
^
time.c:6:94: error: expected declaration specifiers or '...' before 'tm'
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);
^
time.c:6:105: error: expected declaration specifiers or '...' before 'tm'
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);
^
C:\C\Codes>
Solution
C:\C\Codes>more time.c
#include <stdio.h>
#include <time.h>
int main()
{
time_t t = time(NULL);
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);
}
C:\C\Codes>
Compiling
C:\C\Codes>gcc time.c -o time
C:\C\Codes>
Final Output
C:\C\Codes>time
now: 2018-3-11 15:46:36
C:\C\Codes>
I hope this will helps others too
instead of files use pipes and if u wana use C and not C++ u can use popen like this
#include<stdlib.h>
#include<stdio.h>
FILE *fp= popen("date +F","r");
and use *fp as a normal file pointer with fgets and all
if u wana use c++ strings, fork a child, invoke the command and then pipe it to the parent.
#include <stdlib.h>
#include <iostream>
#include <string>
using namespace std;
string currentday;
int dependPipe[2];
pipe(dependPipe);// make the pipe
if(fork()){//parent
dup2(dependPipe[0],0);//convert parent's std input to pipe's output
close(dependPipe[1]);
getline(cin,currentday);
} else {//child
dup2(dependPipe[1],1);//convert child's std output to pipe's input
close(dependPipe[0]);
system("date +%F");
}
// make a similar 1 for date +T but really i recommend u stick with stuff in time.h GL
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):
An extremely good beginners tutorial on this subject by Zetcode:
Simple operations with datetime on Codeproject:
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.
The answers given above are good CRT answers, but if you want you can also use the Win32 solution to this. It's almost identical but IMO if you're programming for Windows you might as well just use its API (although I don't know if you are programming in Windows).
char* arrDayNames[7] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
SYSTEMTIME st;
GetLocalTime(&st); // Alternatively use GetSystemTime for the UTC version of the time
printf("The current date and time are: %d/%d/%d %d:%d:%d:%d", st.wDay, st.wMonth, st.wYear, st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);
printf("The day is: %s", arrDayNames[st.wDayOfWeek]);
Anyway, this is a Windows solution. I hope it will be helpful for you sometime!
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;
}`
#include<stdio.h>
using namespace std;
int main()
{
printf("%s",__DATE__);
printf("%s",__TIME__);
return 0;
}
time_t rawtime;
time ( &rawtime );
struct tm *timeinfo = localtime ( &rawtime );
You can also use strftime to format the time into a string.
One liner to get local time information: struct tm *tinfo = localtime(&(time_t){time(NULL)});
strftime (C89)
Martin mentioned it, here's an example:
main.c
#include <assert.h>
#include <stdio.h>
#include <time.h>
int main(void) {
time_t t = time(NULL);
struct tm *tm = localtime(&t);
char s[64];
assert(strftime(s, sizeof(s), "%c", tm));
printf("%s\n", s);
return 0;
}
Compile and run:
gcc -std=c89 -Wall -Wextra -pedantic -o main.out main.c
./main.out
Sample output:
Thu Apr 14 22:39:03 2016
The %c specifier produces the same format as ctime.
One advantage of this function is that it returns the number of bytes written, allowing for better error control in case the generated string is too long:
RETURN VALUE
Provided that the result string, including the terminating null byte, does not exceed max bytes, strftime() returns the number of bytes (excluding the terminating null byte) placed in the array s. If the length of the result string (including the terminating null byte) would exceed max bytes, then
strftime() returns 0, and the contents of the array are undefined.
Note that the return value 0 does not necessarily indicate an error. For example, in many locales %p yields an empty string. An empty format string will likewise yield an empty string.
asctime and ctime (C89, deprecated in POSIX 7)
asctime is a convenient way to format a struct tm:
main.c
#include <stdio.h>
#include <time.h>
int main(void) {
time_t t = time(NULL);
struct tm *tm = localtime(&t);
printf("%s", asctime(tm));
return 0;
}
Sample output:
Wed Jun 10 16:10:32 2015
And there is also ctime() which the standard says is a shortcut for:
asctime(localtime())
As mentioned by Jonathan Leffler, the format has the shortcoming of not having timezone information.
POSIX 7 marked those functions as "obsolescent" so they could be removed in future versions:
The standard developers decided to mark the asctime() and asctime_r() functions obsolescent even though asctime() is in the ISO C standard due to the possibility of buffer overflow. The ISO C standard also provides the strftime() function which can be used to avoid these problems.
C++ version of this question: How to get current time and date in C++?
Tested in Ubuntu 16.04.
#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;
}
Source: Stackoverflow.com