C++ [[fallthrough]]


Example

C++17

Whenever a case is ended in a switch, the code of the next case will get executed. This last one can be prevented by using the ´break` statement. As this so-called fallthrough behavior can introduce bugs when not intended, several compilers and static analyzers give a warning on this.

From C++17 on, a standard attribute was introduced to indicate that the warning is not needed when the code is meant to fall through. Compilers can safely give warnings when a case is ended without break or [[fallthrough]] and has at least one statement.

switch(input) {
    case 2011:
    case 2014:
    case 2017:
        std::cout << "Using modern C++" << std::endl;
        [[fallthrough]]; // > No warning
    case 1998:
    case 2003:
        standard = input;
}

See the proposal for more detailed examples on how [[fallthrough]] can be used.