Assigning to [custom typdef] from incompatible type 'int'

Question

In a method in my main.c file, I declare the variable irq_raised, which is of the type irq_type. I've defined irq_type in a typedef in another file and #import it at the top of main.c.

typedef enum
{
  IRQ_NONE = 0x0000,
  IRQ_VBLANK = 0x0001,
  IRQ_HBLANK = 0x0002,
  IRQ_VCOUNT = 0x0004,
  IRQ_TIMER0 = 0x0008,
  IRQ_TIMER1 = 0x0010,
  IRQ_TIMER2 = 0x0020,
  IRQ_TIMER3 = 0x0040,
  IRQ_SERIAL = 0x0080,
  IRQ_DMA0 = 0x0100,
  IRQ_DMA1 = 0x0200,
  IRQ_DMA2 = 0x0400,
  IRQ_DMA3 = 0x0800,
  IRQ_KEYPAD = 0x1000,
  IRQ_GAMEPAK = 0x2000,
} irq_type;

I can assign this variable to one of these like so:

irq_raised = IRQ_NONE;

However, when I attempt to do the following:

irq_raised |= IRQ_HBLANK;

I get the error:

Assigning to 'irq_type' from incompatible type 'int'

Why is this?

Answer 1

In C++ you cannot assign an int directly to an enumerated value without a cast. The bitwise OR operation you are performing results in an int, which you then attempt to assign to a variable of type irq_type without a cast. It is the same problem as you would have here:

irq_type irq = 0;  // error

You can cast the result instead:

irq_type irq = IRQ_NONE;
irq = (irq_type)(irq | IRQ_HBLANK);

Relevant info from the specification:

An enumerator can be promoted to an integer value. However, converting an integer to an enumerator requires an explicit cast, and the results are not defined.