How to convert a string to datetime in C++ - c++

Question

I have a resultset(from a function) which is based on time. But the datetime value is in string format(e.g. "21:5 Jan 23, 11"). I want to convert "21:5 Jan 23, 11" to datetime. How can I do this in C++? I just want to filter records for today. So i need to retrieve the current date from "21:5 Jan 23, 11".
Edit:
I can get the current date and time using
SYSTEMTIME st;
GetSystemTime(&st);
Is there any way to convert "21:5 Jan 23, 11" in the above format?

Answer 1

#include <ctime>
#include <iomanip>
#include <iostream>
#include <sstream>
// Converts UTC time string to a time_t value.
std::time_t getEpochTime(const std::wstring& dateTime)
{
// Let's consider we are getting all the input in
// this format: '2014-07-25T20:17:22Z' (T denotes
// start of Time part, Z denotes UTC zone).
// A better approach would be to pass in the format as well.
static const std::wstring dateTimeFormat{ L"%Y-%m-%dT%H:%M:%SZ" };
// Create a stream which we will use to parse the string,
// which we provide to constructor of stream to fill the buffer.
std::wistringstream ss{ dateTime };
// Create a tm object to store the parsed date and time.
std::tm dt;
// Now we read from buffer using get_time manipulator
// and formatting the input appropriately.
ss >> std::get_time(&dt, dateTimeFormat.c_str());
// Convert the tm structure to time_t value and return.
return std::mktime(&dt);
}

Answer 2

I'm not a C++ programmer but in C you can use strptime http://pubs.opengroup.org/onlinepubs/009695399/functions/strptime.html

Answer 3

The most general C++ way is to use Boost.DateTime.

Answer 4

This is sample program to validate input datetime and parse
#include <iostream>
#include <comutil.h>
#include <iomanip>
bool ValidateAndParseDateTime(const std::wstring & strInputDate, std::tm & date)
{
bool bSuccess = false;
if (!strInputDate.empty())
{
_variant_t varIn = strInputDate.c_str();
if (SUCCEEDED(VariantChangeTypeEx(&varIn, &varIn, GetThreadLocale(), 0, VT_DATE)))
{
std::get_time(&date, strInputDate.c_str());
bSuccess = true;
}
}
}
int main()
{
std::tm date;
std::wstring strInputDate = L"7/20/2020 1:29:37 PM";
if (!ValidateAndParseDateTime(strInputDate, date))
{
//Invalid date and time
}
return 0;
}

Answer 5

If all you need is to check whether two strings have same date or not and if it is guaranteed that strings are in the same format, then there is no need to convert it to date time. You just have to compare the substrings after the first space character. If they are same, then the dates are same. Here is the sample code:
using namespace std;
string getCurrentDate()
{
//Enumeration of the months in the year
const char* months[] = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
//Get the current system date time
SYSTEMTIME st;
GetSystemTime(&st);
//Construct the string in the format "21:5 Jan 23, 11"
ostringstream ss;
ss<<st.wHour<<":"<<st.wMinute<<
" "<<months[st.wMonth-1]<<
" "<<st.wDay<<", "<<st.wYear%1000;
//Extract the string from the stream
return ss.str();
}
string getDateString(const string& s)
{
//Extract the date part from the string "21:5 Jan 23, 11"
//Look for the first space character in the string
string date;
size_t indx = s.find_first_of(' ');
if(indx != string::npos) //If found
{
//Copy the date part
date = s.substr(indx + 1);
}
return date;
}
bool isCurrentDate(const string& s1)
{
//Get the date part from the passed string
string d1 = getDateString(s1);
//Get the date part from the current date
string d2 = getDateString(getCurrentDate());
//Check whether they match
return ! d1.empty() && ! d2.empty() && d1 == d2;
}
int main( void )
{
bool s = isCurrentDate("21:5 Jan 23, 11");
bool s1 = isCurrentDate("21:5 Jan 25, 11");
return 0;
}

Answer 6

In the function "ValidateAndParseDateTime" above, I think it's supposed to return "bSuccess". Without it, caller will always get "Invalid date and time".
{