CODEWITHSUNDEEP
c++
Aryan
Aryan

Reputation: 159

What does X f() mean?

I see this code and I can't understand what it mean. I know how we use default constructor but this is not default constructor. What is this?

class X
{
        ...
};

int main()
{
     X f();
}

Upvotes: 3

Views: 626

Answers (4)

Grijesh Chauhan
Grijesh Chauhan

Reputation: 58271

Its function declaration of name f 

  X          f();
  ^          ^ function   
  return type

function f() takes no arguments and returns a X class object.

for example its definition can be like: 

class X{
   int i;
   // other definition
}

X f(){ 
    X x;
    // some more code
    return x; 
}

In main you can use like: 

int main(){

 X a = f();
 int i = f().i;
}

Upvotes: 2

Ajay
Ajay

Reputation: 18411

Assume you declare a function:

int Random();

And use it:

int main()
{
   int n;
   n = Random();
}

But implement the Random function after main. Or assume that Random function is defined in some header. You need to instruct the compiler that Random is a function implemented in some other source file, or in some library.

Therefore, an expression like:

T foo();

Would always mean a instruction to compiler that there is a function named foo which returns T. It cannot be an object of type T.

Upvotes: 3

Yogi
Yogi

Reputation: 3588

This is a function which doesn't take any argument and returns an object of class X

Upvotes: 1

Alok Save
Alok Save

Reputation: 206526

It declares a function f which takes no parameters and returns a type X.
This is also known as Most Vexing Parse in C++. It is a byproduct of the way the C++ standard defines the interpretation rules for declarations.

Upvotes: 8

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