compilation problem

This is a discussion on compilation problem within the C Programming forums, part of the General Programming Boards category; hi everyone, I was trying to run a program with three files( file1.c, file2.c and file3.h). I have my main ...

  1. #1
    Registered User
    Join Date
    Apr 2002

    compilation problem

    hi everyone,

    I was trying to run a program with three files( file1.c, file2.c and file3.h). I have my main in the file2.c and I put some prototype call from file1.c by using the keyword extern and at the top of file1.c I also have the same protoypes declerations as the ones called in file2.c or see below what I have:

    file2.c /* calls some funtions infile1.c */
    extern int foo()
    extern byte foo2()
    main () .....

    int foo() /* protoype */
    int foo()...

    it is giving me this type error when run:

    ! ./feal8.o(.text+0x0):feal8.c: multiple definition of `Decrypt'
    ! ./feal8.o(.text+0x0):feal8.c: first defined here
    ! ./feal8.o(.text+0xc4):feal8.c: multiple definition of `DissQ1'

    can anyone tell me why it gives me this error ?

  2. #2
    You need to tell the compiler to include a header file only once.

    In every header file, put tags like this (one at the top and bottom):

    headerfile.h -----------------------------------------

    #ifndef __headerfile__
    #define __headerfile__
    ... typedefs ...
    ... extern declarations ...
    #endif __headerfile__

  3. #3
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    #ifndef __headerfile__
    #define __headerfile__
    ... typedefs ...
    ... extern declarations ...
    #endif __headerfile__
    Why does everyone do this? Leading underscores are reserved for the implementation, so unless you are writing a compiler this is incorrect. Otherwise the solution is good.

    My best code is written with the delete key.

  4. #4
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    I rather suspect that you have actual code (and not just prototypes) in the .h file.

    So whilst the include guards are a good idea, and should be used, I don't think they will solve your problem.

    The solution (if this is the problem) is to make sure your .h contains prototypes only, and all the actual code is in the two .c files.

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