#please clear this up for me

This is a discussion on #please clear this up for me within the C++ Programming forums, part of the General Programming Boards category; I'm not clear as to the purpose of these preproccer directives in all my header files #ifndef _FILENAME_HPP_ #define _FILENAME_HPP_ ...

  1. #1
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    #please clear this up for me

    I'm not clear as to the purpose of these preproccer directives in all my header files
    #ifndef _FILENAME_HPP_
    #define _FILENAME_HPP_

    also is it neccary to include <iostream> in my header file if it is included in my main file?

  2. #2
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    by using the #ifndef and #define, you will prevent the compiler from linking the header twice, which will cause you an error. sample:

    #ifndef _HELLO_H
    #define _HELLO_H

    #include <stdio.h>
    #include <iostream.h>

    int something;


    #endif

  3. #3
    Registered User matheo917's Avatar
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    #ifndef _HELLO_H
    #define _HELLO_H

    // your code goes here...

    #endif


    this is a preprocessor directive that is used when a file Hello.h is included within another file....especially when Hello.h is used by many different files, the purpose of this is NOT to have multiple declarations of Hello.h......

    those statements mea: if ... hello.h is not yet defined within the program (or a file system) ....then define it (write it in)......at the end you need... #endif.....to end your if statement

    Regards,
    matheo917

  4. #4
    Used Registerer jdinger's Avatar
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    Re: #please clear this up for me

    Originally posted by rip1968
    also is it neccary to include <iostream> in my header file if it is included in my main file?
    If you call a function from <iostream> anywhere in the *.cpp file associated with the header file, then yes you do need to include it.
    Last edited by jdinger; 05-04-2002 at 08:22 AM.

  5. #5
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    Thanks to you all for clearing these points up.

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