Some exception classes are designed to be used only as base classes to more specific exceptions, for instance, std::exception (the
base class of all standard C++ exceptions), std::logic_error or std::runtime_error.
Catching such generic exception types is usually a bad idea because it implies that the "catch" block is clever enough to handle any type of
exception.
Noncompliant code example
try {
/* code that may throw std::system_error */
} catch (const std::exception &ex) { // Noncompliant
/*...*/
}
Compliant solution
try {
/* code that may throw std::system_error */
} catch (const std::system_error &ex) {
/*...*/
}
Exceptions
There are cases, though, where you want to catch all exceptions because no exceptions should be allowed to escape the function, and generic
catch handlers are excluded from the rule:
- In the main function
- In a class destructor
- In a
noexcept function
- In an
extern "C" function
Additionally, if the catch handler is throwing an exception (either the same as before, with throw; or a new one that may
make more sense to the callers of the function) or is never exiting (because it calls a noreturn function, for instance
exit), then the accurate type of the exception usually does not matter any longer: this case is excluded too.
