CODEWITHSUNDEEP
c++
Johnny Pauling
Johnny Pauling

Reputation: 13407

Temporary structure object constructor odd call

I don't understand this code which should provide a different behavior in C and C++ ( Can code that is valid in both C and C++ produce different behavior when compiled in each language?)

#include <stdio.h>

struct f { };

int main() {
    f();
}

int f() {
    return printf("hello");
}

Why can I call f() in C++? Is it the default constructor (which I don't see by the way, is there another one "implicit"?)? In C++ that is not calling the f() function..

Upvotes: 1

Views: 390

Answers (2)

mfontanini
mfontanini

Reputation: 21900

Every class has an implicit default constructor, unless you define other constructor. This definition of the class f:

struct f { };

Is equivalent to:

struct f { 
    f() = default;
    // same for copy constructors, move constructors, destructor, etc
};

So yes, inside main, you're value initializing(or default initializing, it's the same here), an object of type f.

As of why it's not calling the function f, well, inside main there is no declaration nor definition of the function f available. The only visible symbol named f is the struct defined above.

Upvotes: 2

David Rodr&#237;guez - dribeas
David Rodr&#237;guez - dribeas

Reputation: 208323

In C++, the expression T() where T is a type is the creation of a temporary that is value-initialized. Note that this is different from a call to the constructor in general (in particular it is different for POD types).

Upvotes: 2

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