如何比较“月日期hh：mm：ss”格式的两个时间戳来检查+ ve或-ve值

Question

I checked the stackoverflow site for my answer, i did not get, so i am posting it here.

My problem is:

How to compare two time stamp in format "Month Date hh:mm:ss" ?

I am writing program in C and C++ and the time is in displayable string format.

Example :

time1 = "Mar 21 11:51:20"
time2 = "Mar 21 10:20:05"

I want to compare time1 and tme2 and find out whether time2 is after time1 or not and I need output as true or false , like below:

 if time2 > time1 then 
       i need output as 1 
 or 
       0 or -1 anything

I used difftime(time2,time1) , but it returns the delta time diff between time1 and time2 .
I want to check greater or not.

For any help, thanks in advance

Answer 1

FIRST- use difftime to compare:

you can simply use difftime() function to compare time and return 1 or -1 as follows:

int comparetime(time_t time1,time_t time2){
 return difftime(time1,time2) > 0.0 ? 1 : -1; 
} 

SECOND- Convert string into time:

If you have difficulty to convert string into time_t struct, you can use two functions in sequence:

1. char *strptime(const char *buf, const char *format, struct tm *tm); function. to convert string into struct tm

   Example: to convert date-time string "Mar 21 11:51:20 AM" into struct tm you need three formate strings:

   %b : Month name, can be either the full name or an abbreviation
   %d : Day of the month [1–31].
   %r : Time in AM/PM format of the locale. If not available in the locale time format, defaults to the POSIX time AM/PM format: %I:%M:%S %p .

2. time_t mktime (struct tm * timeptr); function to convert struct tm* to time_t

Below Is my example program:

#include <stdio.h>
#include <time.h>
int main(void){
    time_t t1, t2;
    struct tm *timeptr,tm1, tm2;
    char* time1 = "Mar 21 11:51:20 AM";
    char* time2 = "Mar 21 10:20:05 AM";

    //(1) convert `String to tm`:  
    if(strptime(time1, "%b %d %r",&tm1) == NULL)
            printf("\nstrptime failed\n");          
    if(strptime(time2, "%b %d %r",&tm2) == NULL)
            printf("\nstrptime failed\n");

    //(2)   convert `tm to time_t`:    
    t1 = mktime(&tm1);
    t2 = mktime(&tm2);  

     printf("\n t1 > t2 : %d", comparetime(t1, t2));
     printf("\n t2 > t1 : %d", comparetime(t2, t1));
     printf("\n");
     return 1;
}

And it works as you desire:

 $ ./a.out 
 t1 > t2 : 1
 t2 > t1 : -1

To calculate difference between two dates read: How do you find the difference between two dates in hours, in C?

Answer 2

Look at strptime()

It converts an ASCII string formatted date/time into a struct tm

Answer 3

Here is a very easy way solution to solve your problem. If in your case the comparing depends on the time. If so, you can turn your time variables into string so you can compare them as a string. ONLY if the base of the comparison is the hour and minute and second elements and/or the day. It will look like this:

string time1 = "Mar 21 11:51:20";
string time2 = "Mar 21 10:20:05";

cout<<time1<< endl;
cout<<time2<< endl;
cout<<endl;

if(time1>time2)cout<<time1<< endl;
else cout << time2 << endl;