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Oh dear... I don't understand


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#1 freakyboff   Members   -  Reputation: 122

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Posted 10 August 2001 - 09:12 AM

Can someone either explain to me, or point me in the way of a tutorial or some other information on the net about header files. I''m confused about them. I understand they are used for linking (I think), but in what way. Say if I''m writing an OpenGL application and I want to move all my OpenGL functions to a seperate file. I can just cut & paste the code, but what do I need to put in the header file? I''ve looked at many header files from other sources but I just don''t understand. Please help me!!!

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#2 Pactuul   Members   -  Reputation: 122

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Posted 10 August 2001 - 09:29 AM

In C++ there are two main types of files header files (usually have .h extension) and implementation files (usually have a .c or .cpp extension)

When writing C++ classes esp. you want to put the whole class defination in the .h file and the implementation of each of that classes functions in the .cpp file.

#3 freakyboff   Members   -  Reputation: 122

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Posted 10 August 2001 - 10:05 AM

Ok, thanks for that, now then, what about classes and suchlike? because I have seen headers with variables defined and allsorts of stuff in them

#4 arunvb   Members   -  Reputation: 136

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Posted 10 August 2001 - 10:36 AM

Normally you have all the *Declarations* whether it be variables, functions, classes, structures, enumeration or any other type in the header. All the declarations normally go into the header function.

All the function definitions and all the other implementations go into the cpp file.

E.g .h file will contain :

Sample.h
class CSample
{
int m_iVar;

public:
int add (int iArg);
}

The above is the declaration of the class. It goes into the .h file.

Sample.cpp
int CSample::add (int iArg)
{
m_iVar += iArg;
return m_iVar;
}
The above is the implementation of the class. In our case, the class has only one function. So in the cpp file we just have the implementation of the member function.

But why do we have it this way. Why can''t we have it all in the same file. The reason is C++ is object oriented and you may want to build class hierarchies and sell it so that other developers who can extended or use them in their code. In this case, you need the developer, who is using your class hierarchy, to be able to see what functionality is in the class and you do not want him to see how you''ve implemented the various functionality. So, you build lib files for your class hierarchy and ship both the .h and .lib files to the developer. Now the developer can use your classes by including the .h file in his code but cannot see your implementation since he just has the .lib file and not the .cpp file.
DirectX SDK is a perfect example of this. If you look into the DX folders, you can see a bunch of .h files and .lib files.

Hope this is helps you to get started.
Happy learning C++. It is one of the most interesting languages I''ve come across.
Arun




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