using #ifndef

[John Hanley]

I have a program where both my main.c and program.c files use the program.h
file. So I #include "program.h" in both the .c files. The program.h file
has
#ifndef PROGRAM_H
#define PROGRAM_H
....
#endif

Yet when I build my program, the DJGPP compiler tells me there are multiple
definitions of each of my functions.

Any ideas as to what I doing wrong here?

Thanks!

John

[Richard Tobin]

In article <10************ ***@proxy2.srv. ualberta.ca>,
John Hanley <jd******@telus planet.net> wrote:

Yet when I build my program, the DJGPP compiler tells me there are multiple
definitions of each of my functions.

What's *in* the .h file? It should just be function prototypes, not
complete function definitions.

-- Richard

[Gordon Burditt]

>I have a program where both my main.c and program.c files use the program.h

file. So I #include "program.h" in both the .c files. The program.h file
has
#ifndef PROGRAM_H
#define PROGRAM_H
...
#endif

Yet when I build my program, the DJGPP compiler tells me there are multiple
definitions of each of my functions.

You put the functions in program.h? That's why. Header files are
generally used for function PROTOTYPES, type definitions, #defines,
and sometimes global variables (with "extern"). Defining a function
in a header file, then including it in more than one file which
will be linked together into the same program, is a problem. As
you observed, you get multiple definitions of functions.

#ifndef only works within the same compilation unit. For example,
it WILL protect you from including "program.h" twice, or from
including "program.h" and "foo.h" which includes "program.h" . It
will NOT protect you from "program.h" already being included in
another compilation unit. The compiler is not psychic. It does
not know that you are going to link that compilation unit you already
did and the current one together into the same program. And even if
it was, that's not how #ifndef is supposed to work. You start with
a clean slate at the start of every compilation unit.

Gordon L. Burditt

[Keith Thompson]

"John Hanley" <jd******@telus planet.net> writes:

I have a program where both my main.c and program.c files use the program.h
file. So I #include "program.h" in both the .c files. The program.h file
has
#ifndef PROGRAM_H
#define PROGRAM_H
...
#endif

Yet when I build my program, the DJGPP compiler tells me there are multiple
definitions of each of my functions.

Any ideas as to what I doing wrong here?

Yes, you've got a typo on line 137 of program.c.

Seriously, I don't see anything wrong in what you've posted. Try
narrowing your program down to a set of very small files (say 10-20
lines each) that still exhibits the problem. You just might discover
the problem while you're doing this; if not, post again.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[John Hanley]

You put the functions in program.h? That's why. Header files are
Actually, I didn't. That kind of confuses me too. I just have the
prototypes, 3 structs, and some extern global variables in the header file.
I define these in my program.c file.
#ifndef only works within the same compilation unit. For example,
it WILL protect you from including "program.h" twice, or from
including "program.h" and "foo.h" which includes "program.h" . It
will NOT protect you from "program.h" already being included in
another compilation unit. The compiler is not psychic. It does

I see what you mean. The compiler compiles them each individually
and can't see in to the future to see the .o files will be linked.

I will try a different approach.

Thanks so much!

John

[E. Robert Tisdale]

John Hanley wrote:

I have a program where both my main.c and program.c files use the program.h
file. So I #include "program.h" in both the .c files. The program.h file
has
#ifndef PROGRAM_H
#define PROGRAM_H
...
#endif

Yet when I build my program, the DJGPP compiler tells me there are multiple
definitions of each of my functions.

Any ideas as to what I doing wrong here? cat program.h #ifndef GUARD_PROGRAM_H
#define GUARD_PROGRAM_H 1
#include <stdio.h>
void my_function(voi d); // declaration
#endif//GUARD_PROGRAM_H
cat program.c #include "program.h"

void my_function(voi d) {// definition
fprintf(stdout, "Hello from my_function(voi d)!\n");
}
cat main.c #include <stdlib.h>
#include "program.h"

int main(int argc, char* argv[]) {
my_function();
return EXIT_SUCCESS;
}
gcc -Wall -std=c99 -pedantic -o main main.c program.c

[John Hanley]

> > cat program.h

#ifndef GUARD_PROGRAM_H
#define GUARD_PROGRAM_H 1
#include <stdio.h>
void my_function(voi d); // declaration
#endif//GUARD_PROGRAM_H

> cat program.c

#include "program.h"

void my_function(voi d) {// definition
fprintf(stdout, "Hello from my_function(voi d)!\n");
}

> cat main.c

#include <stdlib.h>
#include "program.h"

int main(int argc, char* argv[]) {
my_function();
return EXIT_SUCCESS;
}

> gcc -Wall -std=c99 -pedantic -o main main.c program.c

This exactly what I did. But in Rhide, it tells me "multple definitions of
_function", and at the command line it tells me "undefined reference to
_function". Yet what you have above is just how I set it up. I am unsure
why it is doing that. Any other ideas?

Thanks!

John

[Keith Thompson]

"John Hanley" <jd******@telus planet.net> writes:

> cat program.h

#ifndef GUARD_PROGRAM_H
#define GUARD_PROGRAM_H 1
#include <stdio.h>
void my_function(voi d); // declaration
#endif//GUARD_PROGRAM_H

> cat program.c

#include "program.h"

void my_function(voi d) {// definition
fprintf(stdout, "Hello from my_function(voi d)!\n");
}

> cat main.c

#include <stdlib.h>
#include "program.h"

int main(int argc, char* argv[]) {
my_function();
return EXIT_SUCCESS;
}

> gcc -Wall -std=c99 -pedantic -o main main.c program.c

This exactly what I did. But in Rhide, it tells me "multple definitions of
_function", and at the command line it tells me "undefined reference to
_function". Yet what you have above is just how I set it up. I am unsure
why it is doing that. Any other ideas?

It's *exactly* what you did?

Try compiling *exactly* the code above and see whether you get the
same error.

If not, as I suggested elsethread, trim your own code down to a short
example that exhibits the problem.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[E. Robert Tisdale]

John Hanley wrote:

> cat program.h #ifndef GUARD_PROGRAM_H
#define GUARD_PROGRAM_H 1
#include <stdio.h>
void my_function(voi d); // declaration
#endif//GUARD_PROGRAM_H

> cat program.c

#include "program.h"

void my_function(voi d) {// definition
fprintf(stdout, "Hello from my_function(voi d)!\n");
}

> cat main.c

#include <stdlib.h>
#include "program.h"

int main(int argc, char* argv[]) {
my_function();
return EXIT_SUCCESS;
}

> gcc -Wall -std=c99 -pedantic -o main main.c program.c

This exactly what I did.

No it isn't exactly what you did.
But in Rhide, it tells me "multple definitions of _function",
and at the command line it tells me "undefined reference to _function".
Yet what you have above is just how I set it up.
I am unsure why it is doing that.
Any other ideas?

Yes.

Stop being such a twit!

We can't read your mind.
Do as Keith Thompson asked:

"Try narrowing your program down to a set of very small files
(say 10-20 lines each) that still exhibits the problem."

Otherwise, stop bothering us.

[John Hanley]

> No it isn't exactly what you did.

Then perhaps you can point out what I did wrong. What I did was declare my
functions, global variables and structs in the .h file. I then #included
them in my .c files as you have done in the example program.

Yes.

Stop being such a twit!

We can't read your mind.
I thought perhaps there was some broader problem I was overlooking. I am
not an experienced
programmer that is why I am asking questions on the newsgroup.
Do as Keith Thompson asked:

"Try narrowing your program down to a set of very small files
(say 10-20 lines each) that still exhibits the problem."
That's fine. I was only replying to your email as you emailed me.

Otherwise, stop bothering us.

No one is forcing you to read my posts and nobody has a gun to your head
telling you
to answer them. If you don't like my questions, you leave ME alone. I
would really
not be a bit offended if you didn't answer my posts.

I was in no way being rude in asking any questions and I appreciated all the
responses I've received as I realize people take time to try and help. You,
however, were rude. You could've been polite about it, but you weren't. I
guess that's your choice...