C programming Makefile.

**Laerehte** · 02-19-2017

Hey guys my first help thread. Hopefully it's on topic. Basically I'm reading Head First C and coding along. I'm currently at a Makefile exercise for a simple calorie calculator output. Heres the code.

hfcal.h:

Code:

void display(float weight, float distance, float coeff);

hfcal.c:

Code:

#include <stdio.h>
#include <hfcal.h>

void display(float weight, float distance, float coeff)
{
    printf("Weight: %3.2F\nDistance: %3.2F\nCalories: %3.2F\n",weight,distance,coeff * weight * distance);
}

test.c:

Code:

#include <stdio.h>
#include <hfcal.h>

int main()
{
    display(115.23,3.2,0.79);
    return 0;

}

Makefile:

Code:

hfcal.o: hfcal.c hfcal.h
    gcc -I./includes -c hfcal.c -o hfcal.o 
treadmill.o: test.c
    gcc -I./includes -c test.c -o treadmill.o
libcal.a: hfcal.o
    ar -rcs ./libs/libcal.a hfcal.o
tread_mill: hfcal.o libcal.a
    gcc treadmill.o -L./libs -lcal -o tread_mill

Current directory:

Code:

.:
hfcal.c  includes  libs  Makefile  test.c

./includes:
hfcal.h  hfcal.o

./libs:
libcal.a

I get the error "make: *** No rule to make target 'hfcal.h', needed by 'hfcal.o'. Stop."
From a little googling I figure that i'm some how using the "gcc -I" dir option incorrectly, but the Makefile code is literally the answer from the book. I'm new to programming, and trying to soak up as much as possible. So any advice is appreciated.

**algorism** · 02-19-2017

You're telling gcc where to find the include files but you're not letting make in on the secret.
Try:

Code:

hfcal.o: hfcal.c includes/hfcal.h

It should also be noted that the tread_mill rule should go first (making it the "default rule"). Presumably that's how the book did it. Order is important.

And libcal.a needs to be libs/libcal.a everywhere.

And of course the indentations must be actual tab characters (not just spaces).

**Laerehte** · 02-20-2017

Thanks algorism for the reply! Could you expand on the tread_mill being first a bit. I'm just assuming you mean?

Code:

gcc -o tread_mill -L./libs/libcal.a treadmill.o

Also my Makefile now looks like:

Code:

hfcal.o: hfcal.c includes/hfcal.h
    gcc -I./includes -c hfcal.c
treadmill.o: test.c includes/hfcal.h
    gcc -I./includes -c test.c -o treadmill.o
libcal.a: hfcal.o
    ar -rcs ./libs/libcal.a hfcal.o
tread_mill: treadmill.o libs/libcal.a
    gcc -o tread_mill -L./libs/libcal.a treadmill.o

which seems to build everything up to libcal.a. Making tread_mill throws an error stating:

Code:

gcc -o tread_mill -L./libs/libcal.a treadmill.o
treadmill.o: In function `main':
test.c:(.text+0x1d): undefined reference to `display'
collect2: error: ld returned 1 exit status
Makefile:8: recipe for target 'tread_mill' failed
make: *** [tread_mill] Error 1

Did I not link the program properly? How's display undefined? I thought I linked it in hcal.o, treadmill.o through the header and "include <hfcal.h>"?
I checked the libcal.a with the nm command and there is a display function inside. After this book i'am definetly going through the GNU make manual -.-....

**algorism** · 02-20-2017

Try this (ensuring that there are real tabs, which seem to be replaced with spaces here). Also make sure you delete libcal.a and the .o files first.

Code:

tread_mill: treadmill.o libs/libcal.a
    gcc -o tread_mill -L./libs treadmill.o -lcal
hfcal.o: hfcal.c includes/hfcal.h
    gcc -I./includes -c hfcal.c
treadmill.o: test.c includes/hfcal.h
    gcc -I./includes -c test.c -o treadmill.o
libs/libcal.a: hfcal.o
    ar -rcs ./libs/libcal.a hfcal.o

By putting tread_mill rule first, when you just say "make" it will build that program. It defaults to the first one. The way you have it, I assume you need to say "make tread_mill".

The -L switch should just be -L./libs (without the libcal.a). And you need the -l switch, -lcal

I'm also assuming that libcal.a needs to be libs/libcal.a everywhere, including the target name (which I changed above). I'm no expert, though.

**stahta01** · 02-20-2017

Instead of

Code:

gcc -o tread_mill -L./libs/libcal.a treadmill.o

I would guess this is more correct.

Code:

gcc -o tread_mill treadmill.o -L./libs/libcal.a

But, I still question this part "-L./libs/libcal.a";
I think it would more likely be "-l./libs/libcal.a".

An -L is normally followed by a folder.
A -l (lower case L) is followed by a library.

Tim S.

**Laerehte** · 02-21-2017

Wow thanks for the replies guys! I had no idea that you had to use the -l (lib) switch in the recipe with the -L (folder). I thought having libs/libcal.a in the prerequisites was enough. Guess not! I also tried the -l./libs/libcal.a (and many variations). They still gave me the same error as -L./libs/libcal.a. Thanks again for the help!

**Laerehte** · 02-21-2017

Just for fun I fiddled around with the Makefile and options to see what works/doesn't with different prerequisites/recipe combinations. It seems that if your' Makefile is in a different directory it can't tell if the file/files it's compiling are up to date. Here's a little tinker on the Makefile to output the *.o files into an obj folder.

Code:

tread_mill: treadmill.o libs/libcal.a
    gcc -o tread_mill ./obj/treadmill.o -L./libs -lcal
hfcal.o: hfcal.c includes/hfcal.h
    gcc -c hfcal.c -o ./obj/hfcal.o -I./includes
treadmill.o: test.c includes/hfcal.h
    gcc -c test.c -o ./obj/treadmill.o -I./includes
libcal.a: hfcal.o
    ar -rcs ./libs/libcal.a ./obj/hfcal.o

Tested and works for me, but like i said if i run "make hfcal.o" it will just keep re-compiling instead of saying "hfcal.o is up to date.".

**algorism** · 02-21-2017

Originally Posted by Laerehte

Tested and works for me, but like i said if i run "make hfcal.o" it will just keep re-compiling instead of saying "hfcal.o is up to date.".

In that case it doesn't work since that's the whole point of a makefile, to not rebuild something if it's not necessary.

The reason it keeps rebuilding it is because the recipe doesn't actually make the target file. I.e., hfcal.o is not obj/hfcal.o.

Try this:

Code:

PROG = tread_mill
INCS = includes
LIBS = libs
OBJS = obj

$(PROG): $(OBJS)/treadmill.o $(LIBS)/libcal.a
    gcc -o $@ $< -L$(LIBS) -lcal
$(OBJS)/hfcal.o: hfcal.c $(INCS)/hfcal.h
    gcc -o $@ -I$(INCS) -c $<
$(OBJS)/treadmill.o: test.c
    gcc -o $@ -I$(INCS) -c $<
$(LIBS)/libcal.a: $(OBJS)/hfcal.o
    ar -rcs $@ $<

.PHONY: clean
clean:
    rm -f $(LIBS)/*.a
    rm -f $(OBJS)/*.o
    rm -f $(PROG)

I've used the automatic variables $@ (target filename) and $< (first prerequisite filename). I've also given the program and the directories variable names. And "make clean" will delete the object files, the library file, and the executable (normally a clean command wouldn't delete the executable!).

Once you get used to it it's actually simpler with the variables.

To make hfcal.o you need to say "make obj/hfcal.o".

**Laerehte** · 02-22-2017

Reading the code you posted is actually a lot easier then what I had worked on algorism

.I also really like that clean target. It saved my fingers a lot of typing

. I re-configured the Makefile to use the folder/filename last night (sadly only have an hour or so a night to tinker/read/program). Thanks for the explanations guys they've cleared up simple makefiles much more than the book i'am reading. I know I should use variables but just for learning sake this is the Makefile:

Code:

tread_mill: obj/treadmill.o libs/libcal.a
    gcc -o tread_mill ./obj/treadmill.o -L./libs -lcal
obj/hfcal.o: hfcal.c includes/hfcal.h
    gcc  -I./includes -c hfcal.c -o ./obj/hfcal.o
obj/treadmill.o: test.c includes/hfcal.h
    gcc -c test.c -o ./obj/treadmill.o -I./includes
libs/libcal.a: obj/hfcal.o
    ar -rcs ./libs/libcal.a ./obj/hfcal.o
clean:
    rm -f ./libs/*.a
    rm -f ./obj/*.o

**algorism** · 02-22-2017

Just to confuse you a little, here's another possibility that will compile your program using "implicit rules". The object files are not in their own directory, though. I also had to change the goal from tread_mill to treadmill, and to use it you have to rename test.c to treadmill.c.

Code:

prog = treadmill
libdir = libs/
incdir = includes/

# These are special variables used by the implicit rules
CC = gcc
CFLAGS = -I$(incdir)
LDFLAGS = -L$(libdir)
LDLIBS = -lcal
ARFLAGS = -rcsU

$(prog): $(prog).o $(libdir)libcal.a(hfcal.o)
hfcal.o: $(incdir)hfcal.h
$(libdir)libcal.a(hfcal.o): hfcal.o

.PHONY: clean
clean:
    -rm -f $(libdir)*.a *.o $(prog)

**Laerehte** · 02-23-2017

I'll have to do a little more reading in the make manual to understand that :P.

**algorism** · 02-23-2017

Originally Posted by Laerehte

I'll have to do a little more reading in the make manual to understand that :P.

The basic idea is that make can create the recipes automatically from built-in "pattern rules" and using the special variables CC, CFLAGS, etc.

The other little wrinkle is that we can refer to a single object file in a library like this: libcal.a(hfcal.o)

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