How to pass a class/object through constructor in C++

Question

I want to make a wrapper Filer class to work with fstream library.

Thus, I want to pass an instance of fstream class through constructor of my own Filer class, which led to this code:

Filer::Filer(fstream fileObject)
{
    fileObject this->fileObj;
};

Though when I compile it, an error is thrown that :

1>Filer.cpp(10): error C2143: syntax error : missing ';' before 'this'

While when I do this:

Filer::Filer(fstream fileObject)
{
    this->fileObj = fileObject;
};

It throws this errors which complains that fstream could not be assigned in such way;

error C2679: binary '=' : no operator found which takes a right-hand operand of type 'std::fstream' (or there is no acceptable conversion)

How should I then make my constructor accept an object of type fstream?

John Zwinck · Accepted Answer · 2014-11-07 12:47:22Z

5

What you've got there is not C++. Try this:

Filer::Filer(fstream& fileObject)
  : fileObj(fileObject)
{
}

That uses an "initialization list" to store a reference to fileObject which must be declared as a member of the class. And you must use references, because streams are not copyable.

answered Nov 7, 2014 at 12:47

John Zwinck

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2 Comments

Mostafa Talebi Over a year ago

Well, can I ask you when in the header file we are specifying the class, what type should be assigned to fileObj ? I mean how should we declare fileObj ? string fileObj; actually does not work

Captain Obvlious Over a year ago

@MostafaTalebi of course it doesn't work, fstream is not a string and string is not a fstream. Declare fileObj as a reference to a fstream - std::fstream& fileObj.

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