CODEWITHSUNDEEP
c++functiondata-structuresstruct
basak
basak

Reputation: 1929

Using struct name as a function

I'm trying to understand what the following line does:

BStats stats = BStats();

The struct is defined as follows:

struct BStats
{
    unsigned a;
    unsigned b;

    BStats& operator+=(const BStats& rhs)
    {
        this->a += rhs.a;
        this->b += rhs.b;
        return *this;
    }
};

But I have no idea about what this line does. Is it calling the default constructor?

Upvotes: 0

Views: 544

Answers (3)

David Rodríguez - dribeas
David Rodríguez - dribeas

Reputation: 208333

The expression BStats() is described in the standard in 5.2.3/2:

The expression T(), where T is a simple-type-specifier (7.1.5.2) for a non-array complete object type or the (possibly cv-qualified) void type, creates an rvalue of the specified type, which is value-initialized.

That is, the expression creates an rvalue of Bstats type that is value-initialized. In your particular case, value-initialization means that the two members of the BStats struct will be set to zero.

Note that this is different than the behavior of calling the default-constructor that is mentioned in other answers, as the default constructor will not guarantee that the members are set to 0.

Upvotes: 3

Odinn
Odinn

Reputation: 808

In C++ Classes and Structs are almost the same (the difference is that C++ structs are classes with public as the default attribute where a class's is private) so it's like calling a constructor.

Upvotes: 0

Fred
Fred

Reputation: 4954

Just like any class, a struct has a default constructor automatically created by the compiler. In your case, BStats() simply calls the default constructor, although the explicit call is useless.

Upvotes: 0

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