Default constructor in C

Question

Is there a way to have some kind of default constructor (like a C++ one) for C user types defined with a structure?

I already have a macro which works like a fast in

Answer 1

You can write a function that returns the C struct:

struct file create_file(int i, float f) {
    struct file obj = { i, f };
    // other code here...
    return obj;
}

If you wonder whether you can have "normal" member functions in C. Well, you can to some extent. I prefer the object-as-first-argument style. You pass a pointer to your struct as the first argument. This way, you can have several functions, defining the interface to your objects:

int file_get_integer(struct file *self) { return self->i; }
float file_get_float(struct file *self) { return self->f; }

If you write in that style, what you have at the end is an abstract data-type. I've seen guys emulating the member function call syntax used in C++ by having function pointers into their struct and then doing:

obj.get_integer(&obj);

It's used by the linux kernel for defining the interface to file system drivers. It's a style of writing that one may like, or may not like. I don't like it too much, because i keep using members of structures for data and not for emulating member functions calls to look like in popular object oriented languages.