C++ Cookbook

13.3. Writing and Reading Dates and Times

Problem

You need to display or read dates and times using local formatting conventions.

Solution

Use the time_t type and tm struct from <ctime>, and the date and time facets provided in <locale>, to write and read dates and times (facets are described in the discussion in a moment). See Example 13-4 for a sample.

Example 13-4. Writing and reading dates

#include <iostream> #include <ctime> #include <locale> #include <sstream> #include <iterator> using namespace std; void translateDate(istream& in, ostream& out) { // Create a date reader const time_get<char>& dateReader = use_facet<time_get<char> >(in.getloc()); // Create a state object, which the facets will use to tell // us if there was a problem. ios_base::iostate state = 0; // End marker istreambuf_iterator<char> end; tm t; // Time struct (from <ctime>) // Now that all that's out of the way, read in the date from // the input stream and put it in a time struct. dateReader.get_date(in, end, in, state, &t); // Now the date is in a tm struct. Print it to the out stream // using its locale. Make sure you only print out what you // know is valid in t. if (state == 0 || state == ios_base::eofbit) { // The read succeeded. const time_put<char>& dateWriter = use_facet<time_put<char> >(out.getloc()); char fmt[] = "%x"; if (dateWriter.put(out, out, out.fill(), &t, &fmt[0], &fmt[2]).failed()) cerr << "Unable to write to output stream.\n"; } else { cerr << "Unable to read cin!\n"; } } int main() { cin.imbue(locale("english")); ...