Converting enum to enum via int in C ++
Is it possible to convert an enum to another enum using int conversion as shown below? It looks like gcc for x64 has no problem with this, but can we expect something different with other compilers and platforms?
What happens when a
equals A_third
and has no equivalent in enum_B
?
enum enum_A {
A_first = 0,
A_second,
A_third
};
enum enum_B {
B_first = 0,
B_second
};
enum_A a = A_first;
enum_B b;
b = enum_B(int(a));
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You have to be careful when doing this, because of some edge cases:
From the C ++ 11 standard (§7.2.6):
For an enumeration whose base type is not fixed, the base type is an integral type that can represent all the counter values defined in the enumeration. If an integral type cannot represent all the values of an enumerator, the enumeration is ill-formed. it is implementation-defined which integral type is used as the base type, except that the base type must not be larger than int if the enumerator value cannot be placed into an int or unsigned int.
This means it is possible that enum
more than int
, so the conversion from enum
to int
may fail with undefined results.
With the above, can be converted int
to enum
, resulting in an enumerator value that is enum
not explicitly specified. Informally, you can think of it enum
as an integral type with multiple values explicitly identified using labels.
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