Decorator Help

Can somebody explain how this code works? Like main() and such.

Code:

---

#include <string>
#include <iostream>


using namespace std;

class Paragraph
{
public:
  Paragraph(const string& inInitialText) : mText(inInitialText) {}
       
  virtual string getHTML() const { return mText; }

protected:
  string mText;       
};

class BoldParagraph : public Paragraph
{
public:
  BoldParagraph(const Paragraph& inParagraph) :
    Paragraph(""), mWrapped(inParagraph) {}

  virtual string getHTML() const {
    return "<B>" + mWrapped.getHTML() + "</B>";
  }

protected:
  const Paragraph& mWrapped;
};

class ItalicParagraph : public Paragraph
{
public:
  ItalicParagraph(const Paragraph& inParagraph) :
    Paragraph(""), mWrapped(inParagraph) {}

  virtual string getHTML() const {
    return "<I>" + mWrapped.getHTML() + "</I>";
  }

protected:
  const Paragraph& mWrapped;
};



int main(int argc, char** argv)
{
  Paragraph p("A party? For me? Thanks!");

  // Bold
  cout << BoldParagraph(p).getHTML() << endl;

  // Bold and Italic
  cout << ItalicParagraph(BoldParagraph(p)).getHTML() << endl;
}

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Output:

Quote:

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<B>A party? For me? Thanks!</B>
<I><B>A party? For me? Thanks!</B></I>

---

I'll be the tutorials here at cprogramming can.

Read up on

1. Constructors.
2. Inheritance
3. Virtual member functions

highly recommend

Accelerated C++: Practical Programming by Example by Andrew Koenig and Barbara E. Moo

Kuphryn

Quote:

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Originally Posted by Dante Shamest

Read up on

1. Constructors.
2. Inheritance
3. Virtual member functions

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I know about all those things.

What I don't get is why apparently .getHTML() is getting called twice in the last line. What's happening?

And further more the following line only calls .getHTML() twice, because of something to do with copy constructors:

cout << BoldParagraph(BoldParagraph(p)).getHTML() << endl;

BoldParagraph is-a Paragraph, which allows it to be passed to the ItalicParagraph constructor. You call ItalicParagraph::getHtml which internally calls Paragraph::getHtml

Quote:

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Originally Posted by King Mir

What I don't get is why apparently .getHTML() is getting called twice in the last line.

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ItalicParagraph's getHTML() adds <I></I> around BoldParagraphy's getHTML() which adds <B></B> around Paragraph's getHTML() which is "A party? For me? Thanks!"

I get it now. Thanks. I simmply missed the fact that BoldParagraph and ItalicParagraph call the wrapped Paragraph's .getHTML.