How to check if enum value is valid?

Question

I am reading an enum value from a binary file and would like to check if the value is really part of the enum values. How can I do it?

Answer 1

In C++ 11 there is a better way if you are prepared to list your enum values as template parameters. You can look at this as a good thing, allowing you to accept subsets of the valid enum values in different contexts; often useful when parsing codes from external sources.

A possible useful addition to the example below would be some static assertions around the underlying type of EnumType relative to IntType to avoid truncation issues. Left as an exercise.

#include 

template class EnumCheck;

template class EnumCheck
{
public:
    template
    static bool constexpr is_value(IntType) { return false; }
};

template
class EnumCheck : private EnumCheck
{
    using super = EnumCheck;

public:
    template
    static bool constexpr is_value(IntType v)
    {
        return v == static_cast(V) || super::is_value(v);
    }
};

enum class Test {
    A = 1,
    C = 3,
    E = 5
};

using TestCheck = EnumCheck;

void check_value(int v)
{
    if (TestCheck::is_value(v))
        printf("%d is OK\n", v);
    else
        printf("%d is not OK\n", v);
}

int main()
{
    for (int i = 0; i < 10; ++i)
        check_value(i);
}