No Value-command?

[GoranGaming]

Hello!
I was just wondering if there is a command that tests if a variable has a value or not. As an example:

int x = 5;

while(x has a value){
   do something;
}

In this case the program would "do something" forever since x's value doesn't change.

int x;

while(x has a value){
   do something;
}

And in this case nothing would happen. Do you get what I mean? Anyway, is there such a command?

[JLBorges]

C++14: std::optional<> http://en.cppreference.com/w/cpp/utility/optional

boost::optional<> http://www.boost.org/doc/libs/1_53_0/libs/optional/doc/html/index.html

[Marcos Modenesi]

int x = 5;
while (x == a_value){
   cout << "x equals a_value;
} 

as you said, this would hang the app, as it's an infinite loop.

In your second case:

int x;

while(x has a value){
   do something;
}

it is said that x is uninitialized. That doesn't mean it has no value . It just means that you don't know its value. It's garbage, it may be 7 or 100 or probably some big number 1989381231. int x designs a lacation in memory that will be interpreted as an int. Since you don't inicialize it, what is there inside that memory location is completely unknown. But it's something.

[GoranGaming]

Okay, I'm sorry then. I meant, is there a way to test if a variable is initialized or not? :)

[Marcos Modenesi]

There is no way in C++ of knowing if a variable is initielized or not. You should check its value using the comparison operator if (x == a_value)

[LB]

All variables always have a value, initialized or not. You have to use another variable to remember if it was initialized, and std::optional/boost::optional does that for you.

[Lodger]

If you always initialise your variables, you won't have to check...

[GoranGaming]

... Did you really think that I was going to use it for that? I wanted a loop to continue until the last part of an array was initialized.

[Marcos Modenesi]

If you find the question answered, you should mark the thread as solved.