将数字传递给期望枚举的函数时，为什么没有得到错误（或至少警告）？

Question

I'm using gcc for an ARM Cortex M4 and doing the following:

uint32_t SetGyroInterruptBits(enum Gyr_Int_Set_Bits BitMap)
{
//    Code Here
return RelevantValue;

}

I created the enums as follows:

enum Gyr_Int_Set_Bits 
{
    HR_FILT = 0x80,
    AM_FILT = 0x40,
    HR_Z_AXIS = 0x20,
    HR_Y_AXIS = 0x10,
    HR_X_AXIS = 0x08,
    AM_Z_AXIS = 0x04,
    AM_Y_AXIS = 0x02,
    AM_X_AXIS = 0x01,
};

When I call this function as follows:

SetGyroInterruptBits(34);

I expected to get at least a warning telling me I should be passing an enum. However, it compiles completely happily. I thought this was an advantage of enums over just using a #define. Is it a warning you have to specifically ask the compiler to check for or do I just misunderstand? Is using a #define just as good in this instance?

Answer 1

In C an enumeration is just a symbolic compile-time constant of type int . You can assign any int value to an enumeration, even if it's not a valid value for the enumeration.

Passing the integer value 34 is the same as passing HR_Z_AXIS | AM_Y_AXIS HR_Z_AXIS | AM_Y_AXIS .