what is the default value of enum variable?

Question

I have a question about enum variable in c++:

type enmu {
   DAY1 = 1,
   DAY2,
   DAY3,
   DAY4
} DAYS;

void main() {
   DAYS days;
}

then what is the default value of days?

score 8 · Accepted Answer · answered Aug 20 '12 at 12:26

8

It's uninitialized and undefined behavior to read the value.

Just like saying

int x;

x doesn't have a value until you initialize it.

answered Aug 20 '12 at 12:26

Luchian Grigore

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ok, then if I do this: if(days) {//do something},what will happen? – Aug 20 '12 at 12:28
@ratzip anything can happen. It's undefined behavior if `days` wasn't initialized. – Luchian Grigore Aug 20 '12 at 12:28
what you mean by undefined behavior? can you give a example? – Aug 20 '12 at 12:29
@ratzip what's confusing? You wanted examples of what undefined behavior is, right? – Luchian Grigore Aug 20 '12 at 12:33
in my case, what default value will be? – Aug 20 '12 at 12:36
@ratzip there is none. The `if` would be illegal. – Luchian Grigore Aug 20 '12 at 12:37
thank you man, I read my code again, and figure it out now,thank you very much! – Aug 20 '12 at 12:39

score 2 · Answer 2 · answered Aug 20 '12 at 12:39

then what is the default value of days?`

Like for any automatic object, the value of the days object is indeterrminate.

Now if you declared your object with the static specifier:

static DAYS days;

Then like for any static object of an arithmetic type, the initial value would be 0.

score 1 · Answer 3 · answered Aug 20 '12 at 12:27

1

Enumerations behave pretty much like integers, i.e. they don't have a well-defined default value. You cannot read the variable's value before initializing it without invoking undefined behavior.

answered Aug 20 '12 at 12:27

unwind

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score 0 · Answer 4 · answered Aug 20 '12 at 12:37

BTW, adding to the words, said before: you really do may have default value for a static enum variable. But be carefull -- it will be 0 (as well as all other static variables). Consider following code:

#include <iostream>

enum _t_test {
                test_1 = 1,
                test_2 = 2,
                test_3 = 3,
             };

static enum _t_test t;

int main()
{
    using namespace std;
    cout << "Value of t is: " << t;
    return 0;

}

It will print 0, but your enums are in range from 1..3. So be aware of it.

what is the default value of enum variable?

4 Answers4