Convert a String to a Date in C++

Convert date in string to Date changing format in C

Check if your system has the function strptime. It's part of POSIX and will do the parsing of the string for you. To convert in the opposite direction there's the C standard function strftime.

Building a date string in c

I would consider using ctime and/or strftime. It might get you what you want without messing too much with strings and time fields.

With strftime:

char text[100];
time_t now = time(NULL);
struct tm *t = localtime(&now);

strftime(text, sizeof(text)-1, "%d %m %Y %H:%M", t);
printf("Current Date: %s", text);

Convert string to time_t in c

If the non-standard C function strptime() allowed:

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

// Return -1 on error
time_t DR_string_to_time(const char *s) {
  // Get current year
  time_t t = time(NULL);
  if (t == -1) {
    return -1;
  }
  struct tm *now = localtime(&t);
  if (now == NULL) {
    return -1;
  }

  // Assume current year
  struct tm DR_time = {.tm_year = now->tm_year, .tm_isdst = -1}; 
  if (strptime(s, "%b %d %H:%M", &DR_time) == NULL) {
    return -1;
  }
  t = mktime(&DR_time);
  return t;
}

Note: "%b %d %H:%M" (month, day, hour, minute) does not contain the year, so code needs some year to form a time_t.

How to convert C date string into an integer?

How to convert C date string into an integer?

Compare correctly

As OP's date strings are in chronological and lexicographical order, a conversion is not needed (unless one has negative years).

// if (date1 < date2 < date3){ 
if (strcmp(date1, date2) < 0 && strcmp(date2, date3) < 0) {

Convert string to time_t

If one wants to still convert, use sscanf() to parse the string. Pay special attention to possible errors.

Some somewhat tested code:

#include <time.h>

time_t YMD_to_time(const char *ymd) {
  if (ymd == NULL) {
    return (time_t)-1;
  }

  struct tm tm = {0}; // Important: initialize all members to 0
  int n = 0;
  sscanf(ymd, "%4d-%2d-%2d %n", &tm.tm_year, &tm.tm_mon, &tm.tm_mday, &n);

  // Scan incomplete or extra junk?
  if (n == 0 || ymd[n]) {
    return (time_t)-1; // Mal-formed string
  }

  // Could add extra checks for months/days outside primary range, spaces in string, etc.

  // Adjust ranges as struct tm uses different references
  tm.tm_year -= 1900;
  tm.tm_mon--;
  tm.tm_isdst = -1; // Important to get right time for Year-Month-Day 00:00:00 _local time_

  // The following conversion assumes tm is in local time.
  return mktime(&tm); // This may return -1;
}

Usage

time_t t1 = YMD_to_time(date1);
time_t t2 = YMD_to_time(date2);
time_t t3 = YMD_to_time(date3);
if (t1 == -1 || t2 == -1 || t3 == -1) return times_are_not_comparable
if (t1 < t2 && t2 < t3) return times_are_in_order;
return times_not_in_order;

How convert string to datetime c++?

To access date and time related functions and structures, you would need to include header file in your C++ program.

There are four time-related types: clock_t, time_t, size_t, and tm. The types clock_t, size_t and time_t are capable of representing the system time and date as some sort of integer.

The structure type tm holds the date and time in the form of a C structure having the following elements:

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
}

Considering that you have the data string in the following format "YYY-MM-DD HH:MM:SS", the subsequent code below show how to convert the string in a date structure:

#include <iostream>
#include <ctime>
#include <string.h>
#include <cstdlib>

using std::cout;
using std::endl;

int main(int argc, char* argv[])
{
    char date[] = "2012-05-06 21:47:59";
    tm *ltm = new tm;

    char* pch;
    pch = strtok(date, " ,.-:");
    ltm->tm_year = atoi(pch); //get the year value
    ltm->tm_mon = atoi(strtok(NULL, " ,.-:"));  //get the month value
    ltm->tm_mday = atoi(strtok(NULL, " ,.-:")); //get the day value
    ltm->tm_hour = atoi(strtok(NULL, " ,.-:")); //get the hour value
    ltm->tm_min = atoi(strtok(NULL, " ,.-:")); //get the min value
    ltm->tm_sec = atoi(strtok(NULL, " ,.-:")); //get the sec value

    // print various components of tm structure.
    cout << "Year: "<< ltm->tm_year << endl;
    cout << "Month: "<< ltm->tm_mon<< endl;
    cout << "Day: "<< ltm->tm_mday << endl;
    cout << "Time: "<< ltm->tm_hour << ":";
    cout << ltm->tm_min << ":";
    cout << ltm->tm_sec << endl;

    delete ltm;
    return 0;   
}

Output:

Year: 2012
Month: 5
Day: 6
Time: 21:47:59

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