What is the function structname (void){num_threads = std::thread::hardware_concurrency();} for in c++? How can I understand it?

Question

When I reading code in project of my interest, I come across the function in struct without function name, and maybe it is not the lambda expression capture->return-type{body} either, i just donnot know what kind of this function is?

// file.cc
struct AppSettings
{

    std::string mesh_name;

    std::size_t num_threads;

    AppSettings (void)
    {
        num_threads = std::thread::hardware_concurrency();
    }
};

anyone knows how should i understand this function
AppSettings (void) {num_threads = std::thread::hardware_concurrency();}?

If you know about lambda expressions but not constructors, you may have begun your C++ studies at the wrong end. — molbdnilo, Jan 02 '19 at 15:26
Thank you for your answer, i am almost a beginner of c++... i am used to the common usage of the constructor but forget the default one — philleeroi, Jan 02 '19 at 15:26

score 2 · Answer 1 · answered Jan 02 '19 at 15:16

2

That is the class's constructor.

This is a special member function that's automatically executed when an instance of the class is instantiated.

Giving it the parameter list (void) is an old-fashioned way of giving it the parameter list (), i.e. no parameters.

For more information, consult the chapter in your C++ book about classes (bearing in mind that struct introduces a class).

answered Jan 02 '19 at 15:16

Lightness Races in Orbit

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Thank you for your answer. Maybe I really should learn the c++ primer more carefully.... – philleeroi Jan 02 '19 at 15:29
@PhilLee Might not be a bad idea ;) – Lightness Races in Orbit Jan 02 '19 at 15:29

What is the function structname (void){num_threads = std::thread::hardware_concurrency();} for in c++? How can I understand it?

1 Answers1