Why am I getting no warning for enum comparison mismatch? [duplicate]

As far as I know, the compiler does not have obligation to issue a warning when comparing enumerations of different types. I could not find it in the standard. For classic enum types there exist implicit type conversion to int, so the resulting code is perfectly legal. Semantically it is often incorrect to compare enumerations of different types, so since C++ we have a scoped enumeration construction which does not allow implicit conversions. (See the code below).

#include <iostream> using namespace std; enum UE1 // This is an unscoped enumeration (since C) { val11, val12 }; enum UE2 // This is an unscoped enumeration too { val21, // have to use different names for enumeration constants val22 }; enum class SE1 // This is an scoped enumeration (since C++11) { val1, val2 }; enum class SE2 { val1, // can use the same names for the constants val2 // because they are in the different scope }; int main(int, char**) { if (val11 == val22) // implicit conversion from an enum to int is available cout << "UE::val11 is equal to UE::val22" << endl; if (static_cast<int>(SE1::val1) == static_cast<int>(SE2::val1)) // have to apply explicit conversion cout << "SE1::val1 is equal to SE2::val1" << endl; if (SE1::val1 == SE2::val1) // error!!! Cannot make implicit conversions from a scoped enumeration. cout << "SE1::val1 is equal to SE2::val1" << endl; return 0; }