I want to convert a time_t to a string and back again.

I'd like to convert the time to a string using ctime().

I can't seem to find anything on google or the time.h header file, any ideas?

Basically what I'm trying to do is store a date in a file, and then read it back so I can use it as a time_t again.

Also, no library references outside of std,mfc.

One more note, this will have to function on Windows xp and above and that's it.

Edit

All I want to do is convert a time_t into a string(I开发者_Go百科 don't care if it's human readable) and then convert it back to a time_t. I'm basically just trying to store the time_t into a file and read it again(but I don't want any code for that, as there will be more info in the file besides a time_t).

You'll have to write your own function to do that. These functions convert any primitive type (or any type which overloads operator<< and/or operator>>) to a string, and viceversa:

template<typename T>
std::string StringUtils::toString(const T &t) {
    std::ostringstream oss;
    oss << t;
    return oss.str();
}

template<typename T>
T StringUtils::fromString( const std::string& s ) {
    std::istringstream stream( s );
    T t;
    stream >> t;
    return t;
}

ctime() returns a pointer to a character buffer that uses a specific formatting. You could use sprintf() to parse such a string into its individual portions, store them in a struct tm, and use mktime() to convert that to a time_t.

The time_t Wikipedia article article sheds some light on this. The bottom line is that the type of time_t is not guaranteed in the C specification. Here is an example of what you can try:

Try stringstream.

#include <string>
#include <sstream>

time_t seconds;
time(&seconds);

std::stringstream ss;
ss << seconds;
std::string ts = ss.str();

A nice wrapper around the above technique is Boost's lexical_cast:

#include <boost/lexical_cast.hpp>
#include <string>

time_t t;
time(&t);

std::string ts = boost::lexical_cast<std::string>(seconds);

Wikipedia on time_t:

The time_t datatype is a data type in the ISO C library defined for storing system time values. Such values are returned from the standard time() library function. This type is a typedef defined in the standard header. ISO C defines time_t as an arithmetic type, but does not specify any particular type, range, resolution, or encoding for it. Also unspecified are the meanings of arithmetic operations applied to time values.

Unix and POSIX-compliant systems implement the time_t type as a signed integer (typically 32 or 64 bits wide) which represents the number of seconds since the start of the Unix epoch: midnight UTC of January 1, 1970 (not counting leap seconds). Some systems correctly handle negative time values, while others do not. Systems using a 32-bit time_t type are susceptible to the Year 2038 problem.

Convert the time_t to struct tm using gmtime(), then convert the struct tm to plain text (preferably ISO 8601 format) using strftime(). The result will be portable, human readable, and machine readable.

To get back to the time_t, you just parse the string back into a struct tm and use mktime().