Boost
C++ Libraries
...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Adds an error to the current error state.
void
add_error(
error_code ec) noexcept;
This function can be used by custom formatters to report that they received a value that can't be formatted. For instance, it's used by the built-in string formatter when a string with an invalid encoding is supplied.
If the error state is not set before calling this function, the error state
is updated to ec. Otherwise,
the error is ignored. This implies that once the error state is set, it
can't be reset.
No-throw guarantee.