making a program expire

Hi all ... i was just wondering is there is a function that could be used in conjunction with a TM structure to get the system date and time? I am trying to make a program expire by using the below code in the constructor of a class. However i see no function that can fill this structure.

Code:

struct tm today;

//getdate(&today);  /* need a getdate function here */

if(today.tm_year > 1900)
{
	if(today.tm_mon > 6)
	{
	             cout << "Program Error ... Aborting!";
	             exit(1);
	}
}

Im using MSVC++ 6.0 ... thanks for any help

Create a struct tm for the time you want the program to expire
use time() and localtime() to get a struct tm for now
use difftime() to work out what the difference is. When the sign of the result changes, then the time is past.

Right on ... thanks for the reply, ill give that a shot!

Hi again ... just had another question about making a program expire. After i have a TM for the time i want the program to expire, and a TM from the time() and localtime() functions. How would i convert these TM structures into a time_t type, so i could use the difftime() function on them ? Or would it be better to just compare the two TM structures to see if the one from the computer is past the expire TM ?

Code:

void CTest::programExpiration(void)
{
	double difference = 0;
	time_t systime;
	struct tm expire;
	expire.tm_mday = 10;
	expire.tm_mon  = 6;
	expire.tm_year = 2004;
	time(&systime);
	struct tm *today = localtime(&systime);

	//difference = difftime(today, expire);
}

Any help would be appreciated ... thanks again

>How would i convert these TM structures into a time_t type, so i could use the difftime() function on them ?
The mktime function makes a time_t out of a struct tm *.

yes i did try the mktime() function before, and it worked for the "struct tm *today" structure, however does nother for the "struct tm expire" structure. Is there a function that can convert a "struct tm" into a time_t type ?

:P

>Is there a function that can convert a "struct tm" into a time_t type ?
No, but you could always pass the address of expire to make it a pointer.

I tried that also, however the program crashes, and the difftime() return value is always the same no matter how i change the expire TM struct

Code:

void CMk3dpdek::programExpiration(void)
{
	double difference = 0;
	time_t systime, today_t, expire_t;
	struct tm expire;
	expire.tm_mday = 9;
	expire.tm_mon  = 6;
	expire.tm_year = 2004;
	time(&systime);
	struct tm *today = localtime(&systime);
	today_t  = mktime(today);
	expire_t = mktime(&expire);
	difference = difftime(today_t, expire_t);

	cout << endl << "THE DIFF IS : " << difference << endl;
	cout << endl << "TODAY TIME : " << ctime(&today_t);
	cout << endl << "EXPIRE TIME : " << ctime(&expire_t);
}

You didn't normalize the values in expire before calling mktime. This is a good reason to check for return values so that you can check for errors.

Code:

void CMk3dpdek::programExpiration(void)
{
	double difference = 0;
	time_t systime, today_t, expire_t;
	time(&systime);
	struct tm *today = localtime(&systime);
	struct tm expire = *today;
	expire.tm_mday = 14;
	expire.tm_mon  = 6;
	expire.tm_year = 2004 - 1900;
	today_t  = mktime(today);
	expire_t = mktime(&expire);
	difference = difftime(today_t, expire_t);

	cout << endl << "THE DIFF IS : " << difference << endl;
	cout << endl << "TODAY TIME : " << ctime(&today_t);
	cout << endl << "EXPIRE TIME : " << ctime(&expire_t);
}

I think i see what you mean. So by getting the localtime() first then doing ...

Code:

struct tm expire = *today;

I guess that would be a "copy constructor" from one structure to another and make all the values the same.

But ya seems to work now thank you for all the help, guess i just have to add a if statement after the difftime() function and i can test it out.

Thanks again