#define MYCLASS_H ?

In many of the Qt example headers it starts with something like this:

Code:

---

#ifndef MYCLASS_H
#define MYCLASS_H
 
#include ....
 
class myClass : public QSomeClass 
{
...
};

---

What is the meaning and purpouse of the MYCLASS_H definitions?
I have noticed that it does not compile if they don't have the same name as the class in the file.

See Wikipedia: Include guard