Re: Reading and writing a class to a (binary) file

[bearophile]

Omid:

As I am learning D as my first language, it may sound crazy.

D is one of the most complex languages, so your have to learn a 
LOT. Learning about static typing is important, but usually as 
first language I suggest Python, despite Python is not perfect.


But I would appreciate if somebody tell me how to read and 
write a class (say with two objects, an integer an a char[20]) 
to a file (text or binary).

This uses a text file. There are various ways to improve this 
code.


import std.string: format;
import std.stdio: File, writeln;
import std.conv: to;

final class Foo {
    private immutable int x;
    private immutable char[20] txt;

    this(in int x_, in string txt_) pure nothrow {
        this.x = x_;
        this.txt[0 .. txt_.length] = txt_;
        this.txt[txt_.length .. $] = ' ';
    }

    override string toString() const {
        return format("%d %s", x, txt);
    }

    void toFile(File fout) const {
        fout.writef("%x %s\n", x, txt);
    }

    static Foo fromFile(File fin) {
        int xx;
        string s;
        fin.readf("%x %s\n", &xx, &s);
        return new Foo(xx, s);
    }
}

void main() {
    immutable fileName = "foo_test.txt";

    auto fin = File(fileName, "wt");
    (new Foo(10, "First test")).toFile(fin);
    (new Foo(20, "Second test")).toFile(fin);
    fin.close();

    auto fout = File(fileName, "rt");
    writeln(Foo.fromFile(fout));
    writeln(Foo.fromFile(fout));
    fout.close();
}


Bye,
bearophile