Set string as current date

Question

I need to write files with the current date included in the name. Currently this is what I have tried:

    time_t t = time(0);
    struct tm * now = localtime(&t);
    string date=now->tm_mday+'/'+(now->tm_mon+1)+'/'+(now->tm_year+1900);

Preferably I'd like to keep this method of getting the date as I have used it earlier on in my program.

Use [`std::ostringstream`](http://en.cppreference.com/w/cpp/io/basic_ostringstream). `+` doesn't work like you think it does. — πάντα ῥεῖ, May 02 '16 at 16:05
@BenjaminBannier i tried printing it and its just an E symbol — Cameron L, May 02 '16 at 16:16
@πάνταῥεῖ yeah I got that, the point is it doesn't work — Cameron L, May 02 '16 at 16:16
@CameronLyall What _doesn't_ work in particular? The usage is pretty straightforward. — πάντα ῥεῖ, May 02 '16 at 16:18
@πάνταῥεῖ when i print the string it gives a weird symbol. Not the date — Cameron L, May 02 '16 at 16:20
`+` doesn't work like you think it does. `int+char+int+char+int` does not produce a concatenated string of characters. — Drew Dormann, May 02 '16 at 16:29

Jerry Coffin · Accepted Answer · 2016-05-02T16:24:04.597

5

I would use std::put_time, something like this:

time_t t = time(0);
struct tm * now = localtime(&t);

your_file << std::put_time(now, "%d/%m/%Y");

If you mean that you need to include the date in the name of a new file, then write to a stringstream, and use your_stream.str() to get a string containing the value.

If (though it strikes me as unlikely) you find that imposes excessive overhead, you could use strftime instead. It writes a date/time directly to a C-style string:

char buffer[64];

strftime(buffer, sizeof(buffer), "%d/%m/%Y", now);

edited May 02 '16 at 16:24

answered May 02 '16 at 16:16

Jerry Coffin

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Sorry, I realise i wasn't very clear. What I'm actually trying to do is write the file name with the date in it. For this I need to be able to have it as a String. – Cameron L May 02 '16 at 16:18

Galik · Answer 2 · 2016-05-02T16:33:14.960

I have often used std::strftime a bit like this:

// use strftime to format time_t into a "date time"
std::string get_date(std::time_t timer)
{
    char buf[sizeof("02/05/2015")]; // big enough for 02/05/2015\0
    std::tm tp = *std::localtime(&timer); // not thread safe
    return {buf, std::strftime(buf, sizeof(buf), "%d/%m/%Y", &tp)};
}

int main()
{
    std::cout << get_date(std::time(0)) << '\n';
}

Output:

02/05/2016

Set string as current date

2 Answers2