CODEWITHSUNDEEP
c++function
makciook
makciook

Reputation: 1555

Strange function

i've got a function declaration in c++ and need to know how it's working:

 template<class x>
    int fun(x, x(*)(x*) );

The first arg is an object of type x. And how to describe the second one?

Upvotes: 1

Views: 234

Answers (3)

John Zwinck
John Zwinck

Reputation: 249143

The second parameter type, where x is a class:

x(*)(x*)

Means "a pointer (*) to a function returning x and taking x*. For example:

class MyClass {};
MyClass doit(MyClass* arg) { return *arg; }
MyClass instance;
int result = fun(instance, doit);

Upvotes: 4

Seth Carnegie
Seth Carnegie

Reputation: 75130

That is the declaration of a template function that returns an integer and takes, as parameters, an x and a pointer to a function that returns an x and takes, as a parameter, an x*.

The part x(*)(x*) is the part that means "a pointer to a function that returns an x and takes, as a parameter, an x*". The first x is the return type, the (*) indicates that it is a pointer to a function (if the parameter had a name, it would be written x(*argname)(x*)), and the third x* is just the argument.

Calling it would look like this:

int f(int* iptr) { return something; }

fun(4, f); // no need for the explicit template parameter because it can be deduced

Or more generally

template<typename x>
x functionname(x* xptr) { return something; }

It will not work in C because, as Daniel White said in a comment, C doesn't have templates.

Upvotes: 5

Uriel Frankel
Uriel Frankel

Reputation: 14612

It is a pointer to a function that return the object of type x, and got one parameter of a pointer to the type x.

Upvotes: 1

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