Makefiles!

Can't get my head around them!
I have myfunctions.h:

Code:

#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

extern int triangularnumber (int number);
#endif

myfunctions.c:

Code:

#include <stdio.h>

int triangularnumber ( int number )
{
int result, i, number_adj;
result = number;
for (i = 1; i < number; i++)
{
number_adj = number - i;
result = result + number_adj;
}
return result;
}

And a program disjointsubset.c:
Which is quite big but has this line:

Code:

if(number_equal >= triangularnumber (no_of_rows_count - 1))
{
//code
}

My makefile is called Makefile:

Code:

CFLAGS=-g

default: disjointsubset

myfunctions.o: myfunctions.c myfunctions.h

disjointsubset.o: disjointsubset.c myfunctions.h

main: disjointsubset.o myfunctions.o
	gcc -g -o disjointsubset disjointsubset.o myfunctions.o
clean:
	rm -f *.o disjointsubset
backup:
	tar cf backup.tar disjointsubset.c myfunctions.h myfunctions.c Makefile

And my error:
(From terminal)

Code:

:>make
cc   disjointsubset.o   -o disjointsubset
disjointsubset.o(.text+0x9ed): In function `main':
/home/shill/cprogramming/disjointsubset.c:184: undefined reference to `triangularnumber'
collect2: ld returned 1 exit status
make: *** [disjointsubset] Error 1

Not sure what i'm doing wrong as this is about as simple as i can get it!
Can you spot anything i'm doing wrong?
It all worked when the function was declared inside disjointsubset.c!
Thanks

Code:

#ifndef MYFUNCTIONS_H
#define MYFUNCTIONS_H

extern int triangularnumber (int number);
#endif

I don't think you need extern there (it's just a function prototype, it's not supposed to be have the code in this file).
And I'm assuming you've #include'd "myfunctions.h" in your big file.

default: disjointsubset

should be

default: main

Or better, rename the main target to be disjointsubset.

I suspect you are not including myfunctions.h in your disjointsubset.c. That's what that warning says, anyways.

tabstop is right, you don't need extern for function prototypes [but there's nothing wrong with having the extern there either - it's optional, and it's best if you are consistant - either always or never!]

Also, the "default" target should really be called "all", as that's the common target to use for "make this thing"

Code:

$ make all

--
Mats

Also (but not causing any problems), you have:

Code:

CFLAGS=-g

but you never use CFLAGS. Instead you have this:

Code:

gcc -g -o disjointsubset disjointsubset.o myfunctions.o

A better way would be to use your CFLAGS variable (especially once you start writing larger makefiles):

Code:

CFLAGS=-g -Wall -c
LDFLAGS=-o

default: disjointsubset

myfunctions.o: myfunctions.c myfunctions.h
	gcc $(CFLAGS) myfunctions.c

disjointsubset.o: disjointsubset.c myfunctions.h
	gcc $(CFLAGS) disjointsubset.c

disjointsubset: disjointsubset.o myfunctions.o
	gcc $(LDFLAGS) disjointsubset disjointsubset.o myfunctions.o
clean:
	rm -f *.o disjointsubset
backup:
	tar cf backup.tar disjointsubset.c myfunctions.h myfunctions.c Makefile

Also turn on some warnings (or all warnings with -Wall).

You often replace gcc with $(CC) as well.

It should be noted that Make has built-in rules for compiling C files. It knows that a .o file can be generated from a .c file with

Code:

$(CC) $(CFLAGS) -c file.c -o file.o

So cpjust's Makefile is much more concisely written with

Code:

CFLAGS=-g -Wall -c
LDFLAGS=-o

default: disjointsubset

myfunctions.o: myfunctions.h

disjointsubset.o: myfunctions.h

disjointsubset: disjointsubset.o myfunctions.o
	gcc $(LDFLAGS) disjointsubset disjointsubset.o myfunctions.o
clean:
	rm -f *.o disjointsubset
backup:
	tar cf backup.tar disjointsubset.c myfunctions.h myfunctions.c Makefile

Note that, for example, in the rule disjointsubset.o, you don't have to depend on disjointsubset.c, because that's part of the built-in rule.

Wow, thanks guys, i hadn't included the header file properly, and i've changed the makefile main to disjointsubset.

Works a treat now.
And i've copied dwks makefile example and understand it (which is always good)!

Thanks again everyone.