Simple problem with header file ..

This is a discussion on Simple problem with header file .. within the C Programming forums, part of the General Programming Boards category; Hi, been some time since I programmed in c, so I'm sitting and coding some but I can't seem to ...

  1. #1
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    Oct 2007
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    Simple problem with header file ..

    Hi, been some time since I programmed in c, so I'm sitting and coding some but I can't seem to understand what I do wrong ... my code:

    foo.h:
    Code:
    #ifndef FOO_H_
    #define FOO_H_
    
    extern int getage(char *name);
    
    #endif
    foo.c:
    Code:
    #include "foo.h"
    
    int getage(char *name);
    
    int getage(char *name){
    	return 10;
    }
    wibble.c:
    Code:
    #include "foo.h"
    #include <stdio.h>
    
    int main(){
    	printf("Fred's age: %d\n", getage("Fred"));
    	return 0;
    }

    When I compile: gcc wibble.c -o wibble I get:

    /tmp/ccWbHHtl.o: In function `main':
    wibble.c.text+0xa): undefined reference to `getage'
    collect2: ld returned 1 exit status

    What am I doing wrong?

    thanks.

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    You are not compiling/linking foo.c into your project.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
    Registered User
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    D'OH!

    thanks m8.

  4. #4
    Kernel hacker
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    Code:
    #include "foo.h"
    
    int getage(char *name);
    
    int getage(char *name){
    	return 10;
    }
    Since you are including foo.h (and you should - it makes sure that you don'd mismatch your foo.h prototype and getage's definition), you should not prototype getage() as well as define it.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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