C++ iomanip Library - put_time Function

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Description

This function accesses the output sequence by first constructing an object of type basic_ostream::sentry. Then (if evaluating the sentry object is true), it calls time_put::put (using the stream's selected locale) to perform both the formatting and the insertion operations, adjusting the stream's internal state flags accordingly. Finally, it destroys the sentry object before returning.

It is used to inserts the representation of the time and date information pointed by tmb, formatting it as specified by argument fmt.

Declaration

Following is the declaration for std::put_time function.

template <class charT>
/*unspecified*/ put_time (const struct tm* tmb, const charT* fmt);

Parameters

tmb − Pointer to the object of type struct tm with the date and time information to format. struct tm is a class defined in header <ctime>.

fmt − C-string used by time_put::put as format string. It contains any combination of regular characters and special format specifiers. These format specifiers are replaced by the function to the corresponding values to represent the time specified in tmb.

They all begin with a percentage (%) sign, and are shown below −

Return Value

Unspecified. This function should only be used as a stream manipulator.

Errors are signaled by modifying the stream's internal state flags −

Exceptions

Basic guarantee − if an exception is thrown, the object is in a valid state.

It throws an exception of member type failure if the resulting error state flag is not goodbit and member exceptions was set to throw for that state.

Any exception thrown by an internal operation is caught and handled by the function, setting badbit. If badbit was set on the last call to exceptions, the function rethrows the caught exception.

Data races

Accesses the object pointed by tmb and the array pointed by fmt.

Modifies the stream object where it is inserted.

Concurrent access to the same stream object may cause data races, except for the standard stream objects (cout, cerr, clog, wcout, wcerr and wclog) when these are synchronized with stdio (in this case, no data races are initiated, although no guarantees are given on the order in which characters from multiple threads are inserted).

Example

In below example explains about put_time function.

#include <iostream>
#include <iomanip>
#include <ctime>
#include <chrono>

int main () {
   using std::chrono::system_clock;
   std::time_t tt = system_clock::to_time_t (system_clock::now());

   struct std::tm * ptm = std::localtime(&tt);
   std::cout << "Now (local time): " << std::put_time(ptm,"%c") << '\n';

   return 0;
}