How to convert a string variable containing time to time_t type in c++?

Question

I have a string variable containing time in hh:mm:ss format. How to convert it into time_t type? eg: string time_details = "16:35:12"

Also, how to compare two variables containing time so as to decide which is the earliest? eg : string curr_time = "18:35:21" string user_time = "22:45:31"

Note that time_t encodes the number of seconds since midnight, 1 January 1970 this be careful using it to encode just the time without the date. — Rob K, Jun 26 '12 at 18:18

v2blz · Answer 1 · 2017-02-17T09:23:55.597

73

With C++11 you can now do

struct std::tm tm;
std::istringstream ss("16:35:12");
ss >> std::get_time(&tm, "%H:%M:%S"); // or just %T in this case
std::time_t time = mktime(&tm);

see std::get_time and strftime for reference

edited Feb 17 '17 at 09:23

answered Jul 30 '14 at 12:37

v2blz

761
5
7

2

I think it's worth to mention that std::get_time is **available in GCC from version 5**, you need then `#include ` – MBI Jan 17 '17 at 07:52
1

shouldn't mktime take &tm? – Behrooz Karjoo Feb 08 '17 at 18:59
2

`std::get_time` has also some bugs under VS2013 e.g. here http://stackoverflow.com/questions/32019209/is-this-a-bug-in-stdget-time and here http://stackoverflow.com/questions/35041344/trying-to-use-stdget-time-to-parse-yymmdd-and-failing – Wakan Tanka Feb 16 '17 at 07:53
1

Be warned if working with time zones that mktime expects tm to be a time appropriate to the local time zone. – Joseph Van Riper Sep 06 '19 at 17:08
1

When used on dates, `mktime` was returning -1 for me. Fixed it by changing the first line to `struct std::tm tm = {0};`, – Rumák Mar 24 '21 at 08:48

score 65 · Accepted Answer · answered Jun 26 '12 at 18:22

65

You can use strptime(3) to parse the time, and then mktime(3) to convert it to a time_t:

const char *time_details = "16:35:12";
struct tm tm;
strptime(time_details, "%H:%M:%S", &tm);
time_t t = mktime(&tm);  // t is now your desired time_t

answered Jun 26 '12 at 18:22

Adam Rosenfield

390,455
97
512
589

7

`strptime` is Linux-specific, I believe. – Kyle Strand Mar 09 '16 at 01:04
3

@KyleStrand: It's part of POSIX.1-2001 (and also SUSv2). You're right that it's not standard C or C++, but it's more than just Linux. – Adam Rosenfield Mar 09 '16 at 15:46
Thanks. I should have thought to check that. – Kyle Strand Mar 09 '16 at 16:41
Be careful that the date will still be 1 January 1970, not the day you are running the program – Foxhole Apr 24 '19 at 20:31
Must call memset(&tm, 0, sizeof(tm)) to init !!!! – selfboot Aug 23 '22 at 05:18

score 18 · Answer 3 · answered Jun 26 '12 at 18:12

18

This should work:

int hh, mm, ss;
struct tm when = {0};

sscanf_s(date, "%d:%d:%d", &hh, &mm, &ss);


when.tm_hour = hh;
when.tm_min = mm;
when.tm_sec = ss;

time_t converted;
converted = mktime(&when);

Modify as needed.

answered Jun 26 '12 at 18:12

Mahmoud Al-Qudsi

28,357
12
85
125

1

Note that `sscanf_s` is not the C++ way to handle this, it's the C way (although in this case it will work and is reasonably safe, so no downvote). Using `std::stringstream` and `>>` would be more idiomatic C++. – ssube Jun 26 '12 at 18:16
@peachykeen yes, that is correct. If you post the C++ version, I will upvote :) – Mahmoud Al-Qudsi Jun 26 '12 at 18:21
3

This code can get time, but how about **date** (yyyy-MM-dd)? – Lei Yang Jun 26 '16 at 12:12
@LeiYang I don't see date mentioned anywhere in the question. – Mahmoud Al-Qudsi Mar 11 '17 at 16:43
1

@LeiYang `sscanf(forceNextImportAfter, "%d-%d-%d %d:%d:%d", &year, &month, &day,&hour,&minute,&second)` – OneWorld Oct 09 '18 at 11:07

score 0 · Answer 4 · answered Jul 23 '21 at 19:20

Here's the complete C implementation with date & time.

        enum DateTimeFormat {
            YearMonthDayDash, // "YYYY-MM-DD hh:mm::ss"
            MonthDayYearDash, // "MM-DD-YYYY hh:mm::ss"
            DayMonthYearDash  // "DD-MM-YYYY hh:mm::ss"
        };

        //Uses specific datetime format and returns the Linux epoch time.
        //Returns 0 on error
        static time_t ParseUnixTimeFromDateTimeString(const std::wstring& date, DateTimeFormat dateTimeFormat)
        {
            int YY, MM, DD, hh, mm, ss;
            struct tm when = { 0 };
            int res;

            if (dateTimeFormat == DateTimeFormat::YearMonthDayDash) {
                res = swscanf_s(date.c_str(), L"%d-%d-%d %d:%d:%d", &YY, &MM, &DD, &hh, &mm, &ss);
            }
            else if (dateTimeFormat == DateTimeFormat::MonthDayYearDash) {
                res = swscanf_s(date.c_str(), L"%d-%d-%d %d:%d:%d", &MM, &DD, &YY, &hh, &mm, &ss);
            }
            else if (dateTimeFormat == DateTimeFormat::DayMonthYearDash) {
                res = swscanf_s(date.c_str(), L"%d-%d-%d %d:%d:%d", &DD, &MM, &YY, &hh, &mm, &ss);
            }
            //In case datetime was in bad format, returns 0.
            if (res == EOF || res == 0) {
                return 0;
            }

            when.tm_year = YY - 1900; //Years from 1900
            when.tm_mon = MM - 1; //0-based
            when.tm_mday = DD; //1 based

            when.tm_hour = hh;
            when.tm_min = mm;
            when.tm_sec = ss;

            //Make sure the daylight savings is same as current timezone.
            time_t now = time(0);
            when.tm_isdst = std::localtime(&now)->tm_isdst;

            //Convert the tm struct to the Linux epoch
            time_t converted;
            converted = mktime(&when);

            return converted;
        }

score 0 · Answer 5 · answered Aug 23 '22 at 05:21

0

use strptime.

struct tm tm;
memset(&tm, 0, sizeof(tm));
char *res = strptime(strtime.c_str(), format.c_str(), &tm);
if (res == nullptr) {
    // err process
}
ti = mktime(&tm);

Must init tm, and check the return value.

answered Aug 23 '22 at 05:21

selfboot

1,490
18
23

How to convert a string variable containing time to time_t type in c++?

5 Answers5

Linked

Related