How do I test that an std::error_code is not an error?

Question

I have a method that returns an std::error_code. I am not particularly interested in the error message, only in whether or not the method succeeded.

What is the best way to test that an std::error_code represents a successful operation?

Answer 1

I came across the similar situation when working with the ASIO library. As what one of their blog posts suggests, std::error_code is meant to be tested as follows:

std::error_code ec;
// ...    
if (!ec)
{
  // Success.
}
else
{
  // Failure.
}

Having dug a little deeper, I found this (much more recent) discussion in the C++ Standard Google group, which confirms the statement above but also raises questions about whether the current design of std::error_code is straightforward enough.

Long story short, if you need to simply tell errors from success, !static_cast<bool>(errorCode) is what you need.