Header files

This is a discussion on Header files within the C Programming forums, part of the General Programming Boards category; Hi! I've just created a program (.c) and a header (.h) file with all the functions that I use in ...

  1. #1
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    Header files

    Hi! I've just created a program (.c) and a header (.h) file with all the functions that I use in my program. Of course I don't have any main() function in the header file, which gives me an error: "Undefined symbol _main in module c0.ASM" if I run the .h file. I've also added a line, telling
    Code:
    #include "functions.h"
    to the .c file and if I run the .c file, everything works without errors. So what is the correct way of creating a project? Should the .h file include a main function (which will result to multiple main() declaration) ?

    p.s. I'm using Borland C++ 3.1
    Last edited by nowber; 11-11-2009 at 02:28 PM.

  2. #2
    spurious conceit MK27's Avatar
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    Header files are actually not necessary at all, but if you want to use one, go ahead.

    Anyway, no, there should not be a main() in the .h file. Each program can have only one main(). A header is not intended to used by itself.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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    Ok, so I have a functions.h header file (without the main function) and a main.c file. If I add both of them to a project and run it, I get multiple errors saying:

    _function1 defined in module MAIN.C is duplicated in module FUNCTIONS.H
    _function2 defined in module MAIN.C is duplicated in module FUNCTIONS.H
    etc...

    although I have defined them ONLY in functions.h file. The same error is produced for the array of records, that I've defined in functions.h. Any idea of what I'm doing wrong?

    Here's a small example how it looks in general:

    Code:
    (functions.h)
    
    int number (int low, int high);
    
    struct rec {
    	char name[33];
    	};
    struct rec arr[5]; // array of records
    
    
    int number (int low, int high){
    ... some actions
    }
    
    (main.c)
    
    #include "functions.h"
    
    number(1,50)
    Last edited by nowber; 11-11-2009 at 03:08 PM.

  4. #4
    spurious conceit MK27's Avatar
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    Quote Originally Posted by nowber View Post
    If I add both of them to a project and run it,
    I am not familiar with the Borland compiler, so I presume this means you are doing something with the IDE?

    Anyway, normatively you just include the .h file in your .c file:
    Code:
    #include "myheader.h"
    Note that is not <myheader.h>. This presumes both files are in the same directory.

    Then you just compile the .c file and the .h file will be included.

    [edit] okay, it looks like that is what you are already doing....hmmm
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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