Passing variable between cpp files

I have a variable in my "book.cpp" file named title. I want to pass this variable over to my "page.cpp" file so I can use it to output a page. How do I go about doing this? Here is a portion of my book.cpp file for getting the string:

Code:

---

string Book::getTitle(string title)
{
    size_t title_start;

    title_start = title.find("Title:");

    if (title_start == title.npos)
      return "";
    title = title.substr(title_start+7);
    return title;
}

---

and here is the book.h file class:

Code:

---

class Book {
    ifstream file;
    string title;

    public:
    string getTitle(string title);
    Book(istream& in);
    bool open(istream& in);
};

---

and I am trying to get it over to my page.cpp file:

Code:

---

void Page::output(ofstream& out) const
{
    string title;
    out.open("Page0001.html");
    out << "<title>" << title << "</title>" << endl;
    out.close();
}

---

with this page.h file class:

Code:

---

class Page {
    int lines;
    int pagenumber;
    ifstream file;
    ofstream out;
    vector<string> text;

    public:
    Page(istream& in);
    void setPageNum(int pageNum);
    void addLine(string line);
    void output(ofstream& out) const;
    int getLines() const;
    int getPageNum() const;
};

---

Any help is appreciated!

Generally when thinking of a book, you think that it has pages and not vica-versa. If anything, your book object should handle output rather then your page. If you want your page to be independent of your book, then I would think the best way is to give the page its own title variable and set it at construction.

It just seems unusual to say a page has a title rather then saying a book has a title. (hope this helped somewhat).

I guess you could give the page a pointer to the book that spawned it so that you could make a call like page.BookParent->getTitle();

Well I am building a project that outputs pages as html files. I search for the title given that it starts at "Title:" and ends after the line. Now I just need to get that variable and place it as the <title></title> tags of my html output. That's ALL I need it for!! :(

I don't quite get the question, but if this helps any here's my two cents. If you want to get the title variable inside the page function where it outputs it as "<title>" title "</title>" then just pass a second argument to output(). Or make the variable title a private member of the class and when you call getTitle() it changes the private member. Maybe something like this...?

Code:

---

void Page::output(ofstream& out, string title) const
{
    out.open("Page0001.html");
    out << "<title>" << title << "</title>" << endl;
    out.close();
}

//and use it something like this...

Page p;
Book b;
p.output(outputstream, b.getTitle("title"));

//or even just...
p.output(outputstream,"title");

---

and where do I put the Book b and Page p variables?

Where ever you need to declare them. There's not really a right or wrong place to put them.

Wherever I put them I am getting "b is not a type."

scwizzo was just putting them there to show you an example of how you could call the new modified functions, not something you should copy and use.
Adapt it to your own code - the example, I mean, not the code.

yeah it really doesn't help though because i am not that advanced in c++

What did scwizzo do? scwizzo simpy added "title" to the list of parameters for the function so you can actually pass along the title you wish to write.
Now, incorporate it into your design and carry on as usual.

Alright I can pass it now but I do not want to pass it to the output function. I want to pass it to a function where I can take the passed variable and store it in a variable in the Page ADT. Can anyone help me with that?

Why is it so difficult to pass and store variables?

because I'm not as skilled in C++ as you are!!

Of course not, but this is a simple operation which you have done oh so many times now!

Okay I can pass it to a different function but how do I use this variable globally between all the functions?

We know you're not as skilled as some of the members on the board, but passing and getting variables should be a well developed skill by the time you build classes and ADT's. Anywho, you can make the same variable inside each class as a private member, and have functions that return the value when ever you need it. That would, in a sense, be making the variable (more over the value) global.

To that, there are several solutions:
1) Pass them as arguments to every function you call.
2) Make it global or a class member.

Globals should really, really be avoided unless you need them, however.
The rule is: use as local scope as you can. Consider passing them as arguments instead.

But to your original question, you don't really need more than local scope. All you need is to pass it as an argument!

Okay I pass the title using:

Code:

---

Page p;
    p.passTitle(title);

---

from the Book ADT to the Page ADT. Now passTitle function looks like this:

Code:

---

string Page::passTitle(string theTitle)
{
    title = theTitle;
    return title;
}

---

I can't simply have "title" as a parameter for the output functions because that doesn't work.

You can, but that's up to your implementation.
The function should probably be called something along the lines of SetTitle, as well.
Aside from that, if title is a member variable, then it works like you want it to. I would, however, prefix any member variable with "m_" to identify it as a member variable.

title is a private class member. but it's not working the way it's suppose to....because i use the title variable in my output function and it's not outputting it.

You are not passing an extra argument named "title" to the output function, are you?
If not, then please show the code.

I don't think I am...but here is my code:

This is calling the output function:

Code:

---

output(out, title);

---

and this is the output function:

Code:

---

void Page::output(ofstream& out, string title) const
{
    out.open("Page0001.html");

    out << "<title>" << title << "</title>";

    for(int i = 0; i<text.size(); ++i)
    {
        out << "<pre>" << text.at(i) << "</pre>";
    }
    out.close();
}

---

Quote:

---

Originally Posted by Todd88

Code:

---

void Page::output(ofstream& out, string title) const
{
    out.open("Page0001.html");

    out << "<title>" << title << "</title>";

    for(int i = 0; i<text.size(); ++i)
    {
        out << "<pre>" << text.at(i) << "</pre>";
    }
    out.close();
}

---

---

But you are.
The argument hides the member variable.

how else do I call that then?

Do you fail to understand what you are doing here?

Yes Elysia, I do.

Then you need to take a step back and look at your current implementation.
Your function takes two parameters.
You also have a member variable.
They even share the same name!

Okay I have a constructor named Page which reads from the input file and takes each line of the input file and places it into a vector. Now, I get the title variable from the Book ADT which I pass to the Page ADT. What my problem is, is that I need to fill the vector before passing the title variable to output or else nothing will be printed out but the title. The title passes fine if I use

Code:

---

output(out, title);

---

anywhere but the constructor because like I said, title is not global. I do not know how to do this and this is why I am asking the question.

Alright I fixed it. Thanks a lot for your help Elysia and scwizzo. I really appreciate it!