From: Yong-Kwang Goh <ykgoh AT email DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: A beginner's problem...!
Date: Fri, 09 Feb 2001 22:27:55 +0800
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References: <3A7F202C DOT 12549DCB AT tinyworld DOT co DOT uk>
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Well, the linker encounters 2 copies of the function definition of the
function "sqr". When the preprocessor went through your C source code files
(calc.c and list2101.c), the code

#include "calc.h"

would be replaced by the content of "calc.h". So when your C source code
files are sent to the compiler, it actually looks like this:

/*list2101.c*/
... <== replaced by contents of stdio.h (not shown here)
long sqr(int x); <== note that this line has been replaced by preprocessor
too

int main()
{
 int x;

 printf("Enter an integer value: ");
 scanf("%d", &x);
 printf("\nThe square of %d is %ld.\n", x, sqr);
 return;
}
------------------------------
/*calc.c*/
long sqr(int x); <== note that this line has been replaced by the
preprocessor

long sqr(int x)
{
 return ((long)x * x);
}
-------------------------------

So the linker is confused when the same function is defined twice. I would
suggest you edit your "calc.h" as follows:
-------------------------------
#ifndef CALC_H <== Add this line
#define CALC_H <== Add this as well

/*calc.h*/
long sqr(int x);

#endif <== And lastly, don't forget to add this too.
-------------------------------
See if it solves your problem. It should work.

Yong-Kwang Goh
Singapore

KBZDj wrote:

> I am a c/c++ novice, trying to teach myself with the aid of a couple of
> books and DJGPP and RHIDE. I have just been trying my first attempt at
> including my own header files - but cannot get anywhere. So please can
> anyone help - and sorry for bringing up what is probably a very simple
> problem. The problem is described below - could any replies be sent
> direct to me because I have not subscribed to the mailing list.
>
> PROBLEM
> Using RHIDE, I have 2 c files each of which #includes a header file. The
> code is straight from a Teach Yourself C book. The source files compile,
> but I cannot link them to create an EXE. When building (compiling and
> linking) the files I get the following message:
>
> Compiling: calc.c
> no errors
> Compiling: list2101.c
> no errors
> Creating test.exe
> Error: calc.o: In function 'sqr':
> calc.c(4) Error:multiple definition of 'sqr'
> o:calc.c(4) Error:first defined here
> Error: collect2: ld returned 1 exit status
> There were some errors
>
> The source code of the 3 files is:
>
> /*list2101.c*/
> #include <stdio.h>
> #include "calc.h"
>
> int main()
> {
>  int x;
>
>  printf("Enter an integer value: ");
>  scanf("%d", &x);
>  printf("\nThe square of %d is %ld.\n", x, sqr);
>  return;
> }
> ------------------------------
> /*calc.c*/
> #include "calc.h"
>
> long sqr(int x)
> {
>  return ((long)x * x);
> }
> -------------------------------
> /*calc.h*/
> long sqr(int x);
>
> Any help is greatly appreciated.
> Bruce Carlisle