C ++中Java枚举的.values（）的等效项

Question

I first initially learnt to program in Java and therefore when working with enums, I could use .values() in order to produce an array of all the values in that specific enum. I've noticed that now learning C++, there is not an equivalent method.

What is the best way to tackle this as I'm sure people have come up with decent workarounds?

Answer 1

Doing this in C++ usually requires a special sentinel value inside the enumeration or some preprocessor magic.

If your enumerators are sequential then you can use a simple sentinel value ( end in this case):

enum my_enum {
    a,
    b,
    c,
    my_enum_end,
};

for (int i = 0; my_enum_end != i; ++i) {
    // Loop through all of the enum values.
}

When the enumeration is more complicated and there are gaps between each of the enumerators then you can use the preprocessor:

#define ENUMS(F) F(a, 1) F(b, 5) F(c, 10)
#define AS_ENUM(ID, V) ID = V,
#define AS_VALUE(ID, V) V,
#define AS_ID(ID, V) #ID,

enum my_enum {
    ENUMS(AS_ENUM)
};

my_enum const my_enum_values[] = {ENUMS(AS_VALUE)};
std::string const my_enum_keys[] = {ENUMS(AS_ID)};

for (my_enum const i : my_enum_values) {
    // Loop through all of the enum values.
}
for (auto const& i : my_enum_keys) {
    // Loop through all of the enum keys.
}

Here all of the enumerators are specified in the ENUMS macro rather than inside the enum definition directly.