C ++中的Typedef枚举

Question

I have one typedef like this

typedef enum
{
ONE = 01,
TWO = 02,
THREE = 03
}number_t;

I just defined one member variable as number_t m_number;

so if I return m_number in any other functions what will be returned either ONE or TWO or THREE ?

Answer 1

Since you didn't initialise the variable, it has an indeterminate value .

Thus it could be one of the integers that maps to ONE , TWO or THREE , or any other value.

It's not, in itself, wrong for an enum object to have a value that doesn't map to the enumerator, so that isn't a big problem. However, you cannot legally evaluate an indeterminate value, so you won't be able to safely observe this object until you assign it a value.

As an aside, you're in for a shock when you get to 08 , and even more so if you skip to 010 . Don't use leading zeroes on integer literals unless you really intend to count in octal.

Here's what you ought to do:

enum number_t
{
   ONE   = 1,
   TWO   = 2,
   THREE = 3
};

number_t number = ONE;

Answer 2

Just like any other local variable, if it isn't initialized by your code then the content will be whatever is on the stack and in this case completely random.

If you want to be sure what the value is going to be then intialise it before use, add to your enum something like:

NUMBER_NOT_SET = 0

Then on entry to your function:

number_t m_number = NUMBER_NOT_SET;