Unable to compile with gsl on Mac - c

Question

I am trying to implement gsl_rng.h on a Montecarlo simulation on my MacBook Pro (13-inch, Mid 2012). The simulation is all written in C. My problem is that gcc-6 complains it cannot find the gsl library despite the compilation flags which I think are fine.
The top of declare.h, which is included in all .c files I am working on:
/* __________________ LIBRARIES ___________________*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <gsl/gsl_rng.h>
The error:
fatal error: gsl/gsl_rng.h: No such file or directory
The compilation flags included in my makefile:
INCLUDE = -I/usr/local/Cellar/gsl/2.4/include
LINK = -L/usr/local/Cellar/gsl/2.4/lib -lgsl -lgslcblas
I installed both gcc-6 and gsl via Homebrew.
How can I make gcc-6 find gsl? Are my flags wrong?
The makefile:
CC = g++-6
CFLAGS = -lm -O3 -ansi -pedantic -Wall -Wextra\
-Wconversion -Wredundant-decls -fmax-errors=7\
-Wunsafe-loop-optimizations -Wmissing-braces\
-Wparentheses
# -Wdouble-promotion
INCLUDE = -I/usr/local/Cellar/gsl/2.4/include
LINK = -L/usr/local/Cellar/gsl/2.4/lib -lgsl -lgslcblas
../bin/bidimensional_MC: random.o functions.o subroutines.o\
main.o
$(CC) -o ../bin/bidimensional_MC random.o functions.o\
subroutines.o main.o $(CFLAGS) $(LINK) $(INLCUDE)
random.o: random.c
$(CC) -c random.c -lm -O3 $(CFLAGS) $(INCLUDE)
functions.o: functions.c
$(CC) -c functions.c $(CFLAGS) $(INCLUDE)
main.o: main.c
$(CC) -c main.c $(CFLAGS) $(INCLUDE)
suboutines.o: subroutines.c
$(CC) -c subroutines.c $(CFLAGS) $(INCLUDE)
clean:
rm *.o
The output of ls /usr/local/Cellar/gsl/2.4/include/gsl/ is:
/usr/local/Cellar/gsl/2.4/include/gsl/gsl_rng.h
The output of ls /usr/local/Cellar/gsl/2.4/include/ is:
gsl/
The output of ls /usr/local/Cellar/gsl/2.4/include/gsl/ is too long to post, but everything is there, as it should.
EXTRA INFORMATION:
I am using g++-6 instead of gcc-6 because the cluster in which I'm going to finally execute the simulation requires code to be C++ compliant.

Answer 1

In the makefile, you have (or, more precisely, at one time claimed to have):
random.o: random.c
$(CC) -c random.c -lm -O3 $(CFLAGS)
You shouldn't specify the library when compiling the object file. Your CFLAGS do not include the ${INCLUDE} (or $(INCLUDE)) macro. You need something like:
random.o: random.c
$(CC) -c random.c -O3 $(CFLAGS) $(INCLUDE)
This is a minimal change; I'd add $(INCLUDE) to CFLAGS (and remove the -lm again — you don't even need that on a Mac though it does no specific harm). I'd also add -Werror -Wmissing-prototypes -Wstrict-prototypes, and using -ansi (aka -std=c90) isn't sensible — it is an archaic standard. You should be using -std=c11.
CFLAGS = -O3 -g -std=c11 -pedantic -Wall -Wextra \
-Wconversion -Wredundant-decls -fmax-errors=7 \
-Wunsafe-loop-optimizations -Wmissing-braces \
-Wparentheses $(INCLUDE) \
-Werror -Wmissing-prototypes -Wstrict-prototypes
Also, I added -g to get debugging code. Always include -g, even with optimization. It doesn't have a run-time cost; it does have a benefit if you need to debug the code. Granted, it isn't as easy to debug optimized code, but you can do more than if you don't have -g. Include it in both the 'compilation to object' and the 'linking' phases.
(And, in point of detail, I'd have a bunch of separate macros so that each flag can be turned on or off independently, rather than having to rewrite the whole of CFLAGS. However, that can await another day.)