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This tutorial program introduces asio by showing how to perform a blocking wait on a timer.
We start by including the necessary header files.
All of the asio classes can be used by simply including the "asio.hpp" header file.
#include <iostream> #include <asio.hpp>
All programs that use asio need to have at least one I/O execution context, such as an io_context or thread_pool object. An I/O execution context provides access to I/O functionality. We declare an object of type io_context first thing in the main function.
int main() { asio::io_context io;
Next we declare an object of type asio::steady_timer. The core asio classes that provide I/O functionality (or as in this case timer functionality) always take a reference to an io_context as their first constructor argument. The second argument to the constructor sets the timer to expire 5 seconds from now.
asio::steady_timer t(io, asio::chrono::seconds(5));
In this simple example we perform a blocking wait on the timer. That is, the call to steady_timer::wait() will not return until the timer has expired, 5 seconds after it was created (i.e. not from when the wait starts).
A timer is always in one of two states: "expired" or "not expired". If the steady_timer::wait() function is called on an expired timer, it will return immediately.
t.wait();
Finally we print the obligatory "Hello,
world!" message to show when the timer has expired.
std::cout << "Hello, world!" << std::endl; return 0; }
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