Displaying today's date [closed] - c++

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
Questions asking for code must demonstrate a minimal understanding of the problem being solved. Include attempted solutions, why they didn't work, and the expected results. See also: Stack Overflow question checklist
Closed 9 years ago.
Improve this question
In my program I am trying to display today's date in a day//month//year layout. I've tried using many different ways but I keep getting errors about unsafe use of cTime.
Is there a simple way of getting my program to show the date:
time_t t = time(0); // get time now
struct tm * now = localtime( & t );
cout << (now->tm_year + 1900) << '-'
<< (now->tm_mon + 1) << '-'
<< now->tm_mday
<< endl;
I keep getting "'localtime': This function or variable may be unsafe. Consider using localtime_s instead."
So I did, and now I get
'localtime_s' : function does not take 1 arguments

Answer 1

localtime_s is a Microsoft-specific function that is similar to the C-standard function but with slightly different arguments that are less error-prone. See http://msdn.microsoft.com/en-us/library/a442x3ye.aspx for more information.
That said, if you are using C++, it might be better to use the functions from the chrono part of the C++ standard library. They are easier to use and safe: http://en.cppreference.com/w/cpp/chrono

Answer 2

Unfortunately the standard definition for functions to get from a time_t to formated text all seem to have some potential safety issues, particularly in multi-threaded programs. This leaves you with a choice between going for a vendor specific route or loosing safety in return for portability.
Microsoft specific route:
Details of localtime_s are available here: http://msdn.microsoft.com/en-us/library/a442x3ye%28v=vs.110%29.aspx
Following that something like this should work on visual studio 2012 without warning:
#include <ctime>
#include <iostream>
using namespace std;
int main() {
time_t t = time(0); // get time now
struct tm now;
localtime_s(&now, &t);
cout << (now->tm_year + 1900) << '-'
<< (now->tm_mon + 1) << '-'
<< now->tm_mday
<< endl;
}
However localtime_s is microsoft specific so using it will limit the portability of your code.
Standard compliant but less safe route:
If you prefer standards compliance to safer versions you can use your original version of you code but add the following at the top of the file:
#define _CRT_SECURE_NO_WARNINGS