Kobi – Page 3 – Vorbrodt's C++ Blog

Last weekend (4/4/2021) I was sitting down and working on my San Diego C++ agenda for the 25th upcoming session.

One of things I really like presenting is few riddles from cppquiz.org

I stumbled upon this one: https://cppquiz.org/quiz/question/227 . Simple and easy one.

Here is the code in question:

#include <iostream>

using Func = int();

struct S {
    Func f;
};

int S::f() { return 1; }

int main() {
    S s;
    std::cout << s.f();
}

#include <iostream>

using Func = int();

struct S {

Func f;

};

int S::f() { return 1; }

int main() {

S s;

std::cout << s.f();

}

And the question is what is the output.

So clearly the question is what does the following syntax mean?

Func f;

Func f;

Initially, the “using” part looked like an innocent typedef of a function pointer. But is it?

A quick check with cppinsights.io shows the following

using Func = int();

struct S
{
  int f();
};

using Func = int();

struct S

{

int f();

};

Clearly this is not a function pointer typedef, and we are not defining any “f” as a data member.

Instead, we are actually defining a function named as “f” that returns “int” and takes no params.

So when does it look like a function pointer and when it is not?

Here is a small playground cppinsights.io.

And the gist of it is described in the following snippet:

using Func     = int();                      // function typedef
using Funcp_t  = int(*)();                   // function pointer typedef
using bFuncp_t = std::add_pointer_t<int()>;  // Modern C++ function pointer typedef

using Func = int(); // function typedef

using Funcp_t = int(*)(); // function pointer typedef

using bFuncp_t = std::add_pointer_t<int()>; // Modern C++ function pointer typedef

San Diego C++ Meetup 25th meeting featuring JFrog and Conan!

https://www.meetup.com/San-Diego-CPP/

https://www.meetup.com/San-Diego-CPP/events/277115020/

Agenda

Welcome slides – goals we would like to achieve in San Diego C++ Meetup
This meeting – Hosting JFrog: Conan Package Manager for C++ in Practice

If time permits:
* Shout Out to a great C++ blog – “Vorbrodt’s C++ Blog”
* 3 cppquiz questions
* 2 years of San Diego C++ Books recommendations – a recap!
* An additional New book for this month – “Ace the Trading Systems Developer Interview” With an example of one of the questions

Featuring:
* Conan Package Manager for C++ in Practice

The Conan package manager for C++ is useful in both simple and advanced development environments. Join the Conan team to see it in action, with a simple demo using OSS libraries and tools from ConanCenter, and a more complete demo showing how to create and upload a package including different binaries for different platforms to a private repository. Also, learn about many other unique and innovative advanced Conan features along the way.

Jerry Wiltse Bio: Jerry is a member of the Conan development team, and has been dedicated to build engineering for C and C++ since 2016. He is an avid open-source enthusiast but also deeply focused on enterprise development environments. He is also the narrator and creator of the Conan learning track on the JFrog Academy.

Practical Modern C++

Author: Kobi

Function alias vs Function pointer alias

San Diego C++ Meetup