Class or Struct with a void/function in them? C++

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Hello, I am fairly new to C++ and I was wondering if I can make a struct/class with a function in that to manipulate data within that class. For example I have the following:

C++

#include <sys/stat.h>
#include <fstream>

namespace ByteReader
{
    public class IO
    {
    public:

        struct Stream
        {
            long length;
            long position;
            unsigned char* data;
        };

        struct stat results;

        int fileSize(char* filepath)
        {
            if (stat(filepath, &results) == 0)
                return results.st_size;
            else
                return 0;
        }
    };
}

I was trying to recreate the System::IO::Stream class from microsoft for a little app I'm making. I would like to have the stream setup like and have functions such as ReadInt32 into the struct/class. Is that possible to do? Also how would I pass a filepath as an argument in the class?

ie:
ByteReader::IO br = new ByteReader::IO( filepath );

Posted 3-Jan-13 19:40pm

jakes625

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Comments

Sergey Alexandrovich Kryukov 4-Jan-13 1:44am

I cannot see what's your problem. And there is no such thing as argument in the class. Functions can have argument, and you already use them.
—SA

jakes625 4-Jan-13 1:52am

@-SA I am trying to recreate a stream namespace/class for native C++. For example I want to do the following:

ByteReader::IO br = new ByteReader::IO( @"C:\Folder\Folder\file.log" );
int n = br->ReadInt32();
char* string = br->ReadChars( 8 );

n would return an int, string would return a char array read from that file.

Doesthis help any?

Sergey Alexandrovich Kryukov 4-Jan-13 3:41am

What does it mean: "recreate a namespace"? "Recreate a class"? You are missing something really, really basic.
You should better explain your ultimate goal, without your idea of implementation.
—SA

Philip Stuyck 4-Jan-13 5:44am

by creating a class, he means instantiating one. It would be better to use the correct names for things but for a beginner that is not easy. The amount of stuff to learn is huge. Nevertheless, if you want to create a instance of a class, this is called instantiating. What you get back is an object. An object is an instance of a class.

Sergey Alexandrovich Kryukov 4-Jan-13 7:26am

I agree, but I still cannot understand those "recreating".
—SA

3 solutions

Solution 2

Please see my comments to the question.

Just to give you and idea. Static methods are like old non-class methods, only have access to class (other class members), but instance members has hidden parameter "this". So, in such methods, you can write something like:

C++

this->myField = myMethodParameter;

This will modify the instance's field myField using the method parameter, or anything else, say, some other field.

Please see my past answer: Catch 22 - Pointers to interface objects die when function using them is made static.[^].

You see, I just respond only to your question of the title, as in Solution 1. That solution is basically correct but incomplete. You speculations about "re-creation" are completely unclear; I suspect they are based on some misconception, but I cannot figure out what exactly, sorry.

—SA

Posted 3-Jan-13 21:45pm

Sergey Alexandrovich Kryukov

Comments

Philip Stuyck 4-Jan-13 5:41am

Maybe he is just asking if it is possible to add a method that returns void. And then the answer is yes of course.

Sergey Alexandrovich Kryukov 4-Jan-13 7:25am

Maybe. Good point.
—SA

Solution 3

I miss the point of the struct you defined, but yes, you can do that. I assume you will add more functionality to the class to use it.

Also, in your filesize() api, the parameter filepath should be "const char* filepath" and not "char* filepath".

Posted 4-Jan-13 6:16am

H.Brydon

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Philip Stuyck · Accepted Answer · 2013-01-03T20:47:00

Solution 1

You have to use what is called a constructor to 'pass something to the class'.

C++

class IO{
public:
  IO(const char* filePath){_filePath=filePath;};
private:
  const char* _filePath;
};

The whole point of methods is to do manipulations on the class itself.
I think you should do some more reading. A constructor is really elementary stuff.

Posted 3-Jan-13 20:47pm

Philip Stuyck

Comments

Sergey Alexandrovich Kryukov 4-Jan-13 3:38am

Not necessarily. Any instance function can do that, because it has "this" parameter (hidden).
—SA

Philip Stuyck 4-Jan-13 5:37am

I kept the explanation minimal for a novice user. There is also class methods, which I said nothing about.

Sergey Alexandrovich Kryukov 4-Jan-13 7:24am

A constructor is also a method. If you simply did not even mention the word "constructor", it would be more correct. When it comes to the subject under discussion, constructors are nothing special.
—SA