where can i find out a detailed information about How to write a header file ?

A header file is made up of pre-processor directives, classes, namespaces etc. a good place to look at is cplusplus.com. look at the classes, objects and namespaces chapters...

My God I even had a comp science teacher ask me this.Arrrg one will go mad.

It's simple.Cut a few funtions out of you code and paste them in a file with a .h extension and call #include "your_header_name.h" to include that.

Note: not < > but " " if it's in the current directory else you have to supply the full or relative path.

All the rules are same as normal C++ syntax.

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That was very simple thing.Headers can be used for more things.They can just contain funtions declarations without definitions.In that case it will be used to link to a static library.

Eg.Make a header file with 2 funtion declarations like fun1(); fun2(); only
Include it with a cpp file and call the funtions and compile.

You will get no errors on compile but on linking you will see an error similar to the following:

undefined module fun1() refferenced from Module main.cpp
undefined module fun2() refferenced from Module main.cpp

I hope you understand a header in not really diffrent from a cpp file.Btw you can also include .cpp files.

Eg: #include "wow.cpp"

It is very very simple:


write some functions||define some macros||define structures/classes etc...
DO NOT include a main() function
save it with the name you want
e.g header.txt/cpp/in/out/...
you use it through: #include "..."
if you have variables in your header, do not redeclare them in your programs or it will give you an error "Multiple declaration for variable..."
:p

Even if you include main() in a header and dont declare main() in any other funtion the program will complie and work properly.Headers are just a way to organise code.

well if you include main() in a header that would be more like a program than like a header but anyway you can