Candidate::Candidate ()
{
}
Its not doing any thing. Not writing it as it is can't execute the line:
Candidate *list = new Candidate [10];
Why?
Error: no default constructor exists for the class "Candidate"
2 Answers
To allow your dynamic array allocation, new Candidate[10], a default constructor of Candidate must be available. That is, it must be able to take no arguments. If you provide any of your own constructors for Candidate, regardless of how many arguments they take, the implicit default constructor that is usually defined automatically by the compiler will not be defined. You therefore have to provide it yourself, even if its body is empty. See §12.1/5:
A default constructor for a class
Xis a constructor of classXthat can be called without an argument. If there is no user-declared constructor for classX, a constructor having no parameters is implicitly declared as defaulted (8.4).
Your class would be fine as follows because the compiler will implicitly define a defaulted default constructor:
class Candidate
{ }; // Compiler provides a default constructor
But as soon as you give it any other constructor, the implicit default constructor is not provided any more:
class Candidate
{
public:
Candidate(int x);
// A user-defined constructor is provided so the default constructor
// must be defined explicitly
};
Comments
You probably have an additional constructor in your class. If you have any constructor defined, the compiler won't generate a default one.
4 Comments
Fahad Siddiqui
You mean to say when ever I define a constructor that is not a default, I must give definition of default with it too?
SomeWittyUsername
Basically, yes - if you want to allow creating instances of your class without passing parameters (it won't be called "default" in this case because you define it manually, just a constructor with no parameters)
Benjamin Lindley
It's still called the default constructor, because it is called by default when no argument list is provided. The differentiating term is "compiler-generated".
Joseph Mansfield
@icepack It's still a default constructor, just not a defaulted default constructor (unless you
= default it).
std::vector.