How to format systemtime?

Question

How to format systemtime?

D.D.K-2637 966

Hi,
I'm trying to use std::format to format a string for systemtime (e.g. 1/3/2022)

SYSTEMTIME t;  
const auto today=format("today is: {}", t);

however, when compiled i get an error:

Please show me how to make it work.
I searched for std::format examples with datetime but didn't find it.

Many thansk!

David Lowndes 4,726 Reputation points

2022-03-01T09:24:22.597+00:00

If you need to present the date & time formatted as per a user's Windows locale settings, consider using the GetTimeFormat & GetDateFormat Windows APIs.

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David Lowndes 4,726 Reputation points

2022-03-01T09:24:22.597+00:00

If you need to present the date & time formatted as per a user's Windows locale settings, consider using the GetTimeFormat & GetDateFormat Windows APIs.

Answer 1

Hi @D.D.K-2637 ,

The reason for this error is that SYSTEMTIME is a structure and cannot be used directly in format, so you need to convert SYSTEMTIME to string, the sample code is as follows:
(In order to run the following code you need to refer to the method in this link to turn off the 4996 warning. )

#include <windows.h>  
#include <atlstr.h>  
#include <iostream>  
#include <sstream>  
#include <iomanip>  
#include <format>  
int main()  
{  
    SYSTEMTIME st, lt;  
  
    GetSystemTime(&st);  
    std::string strMessage;  

    CString cstrMessage;  
  
    cstrMessage.Format(_T("%d-%02d-%02d %02d:%02d:%02d.%03d"),  
        st.wYear,  
        st.wMonth,  
        st.wDay,  
        st.wHour,  
        st.wMinute,  
        st.wSecond,  
        st.wMilliseconds);  
  
    strMessage = CT2A(cstrMessage.GetString());  
    std::cout << "System time = " << strMessage << std::endl;  
 
    std::ostringstream ossMessage;  
  
    ossMessage << st.wYear << "-"  
        << std::setw(2) << std::setfill('0') << st.wMonth << "-"  
        << std::setw(2) << std::setfill('0') << st.wDay << " "  
        << std::setw(2) << std::setfill('0') << st.wHour << ":"  
        << std::setw(2) << std::setfill('0') << st.wMinute << ":"  
        << std::setw(2) << std::setfill('0') << st.wSecond << "."  
        << std::setw(3) << std::setfill('0') << st.wMilliseconds;  
  
    strMessage = ossMessage.str();  
    std::cout << "System time = " << strMessage << std::endl;  

    char buffer[256];  
    sprintf(buffer,  
        "%d-%02d-%02d %02d:%02d:%02d.%03d",  
        st.wYear,  
        st.wMonth,  
        st.wDay,  
        st.wHour,  
        st.wMinute,  
        st.wSecond,  
        st.wMilliseconds);  
  
    strMessage = buffer;  
    std::cout << "System time = " << strMessage << std::endl;  
    const auto today = std::format("today is: {}", strMessage);  
    return 0;  
}

You could also use the members in SYSTEMTIME one by one, for example:

const auto today = format("today is: {}/{}/{}", t.wDay,t.wMonth,t.wYear);//e.g. 1/3/2022

Best regards,

Elya

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D.D.K-2637 966 Reputation points

2022-03-01T07:08:34.193+00:00

Hi @YujianYao-MSFT ,

is there any way I can write code like this?

format("today is: {%d-%m-%y}",value);

because I don't know what is the suit data type of value to work with std::format.

in my code %d-%m-%y doesn't work, but I mean, I can format value by string in curly braces.

Thanks you!
YujianYao-MSFT 4,296 Reputation points Microsoft External Staff

2022-03-01T07:28:56.453+00:00

Hi @D.D.K-2637

The easiest way is to execute the program as the following code, does this meet your needs?

#include <windows.h> #include<iostream> #include<vector> #include <format> using namespace std; int main() { SYSTEMTIME st, lt; GetLocalTime(&lt); const auto today = format("today is: {}-{}-{}", lt.wDay, lt.wMonth, lt.wYear); cout << today; return 0; }
YujianYao-MSFT 4,296 Reputation points Microsoft External Staff

2022-03-01T07:37:57.9+00:00

Hi @D.D.K-2637 ,

For its output format, you could refer to this sample:

#include <format> #include <iostream> #include <string> #include <string_view> template <typename... Args> std::string dyna_print(std::string_view rt_fmt_str, Args&&... args) { return std::vformat(rt_fmt_str, std::make_format_args(args...)); } int main() { std::cout << std::format("Hello {}!\n", "world"); std::string fmt; for (int i{}; i != 3; ++i) { fmt += "{} "; // constructs the formatting string std::cout << fmt << " : "; std::cout << dyna_print(fmt, "alpha", 'Z', 3.14, "unused"); std::cout << '\n'; } }

output:

Hello world!
{} : alpha
{} {} : alpha Z
{} {} {} : alpha Z 3.14

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