Question

I have a C API that defines an enum like so:

typedef enum
{
  C_ENUM_VALUE_NONE    = 0,
  C_ENUM_VALUE_APPLE   = (1 << 0),
  C_ENUM_VALUE_BANANA  = (1 << 1),
  C_ENUM_VALUE_COCONUT = (1 << 2),
  // etc.
  C_ENUM_VALUE_ANY     = ~0
} CEnumType;

There is a method that uses the enum, defined as:

void do_something(CEnumType types);

In C, you can call something like:

do_something(C_ENUM_VALUE_APPLE | C_ENUM_VALUE_BANANA);

However, if you try to call it this way in C++ (Linux, g++ compiler), you get an error, invalid conversion from ‘int’ to ‘CEnumType’.

What is the correct way to use this C API from my C++ application?

Answer 1

You need to cast ints to enums in C++, but you can hide the cast in a custom OR operator:

CEnumType operator|(CEnumType lhs, CEnumType rhs) {
    return (CEnumType) ((int)lhs| (int)rhs);
}

With this operator in place, you can write your original

do_something(C_ENUM_VALUE_APPLE | C_ENUM_VALUE_BANANA);

and it will compile and run without a problem.