math.h linkage with file - c

Question

I have a small problem, and I have tried everything to test this function, could you please help me? I need to write a C file that is called "mutual_info.c", and it needs a mathematical function. I have included the library and linked it in the makefile, but it still gives me "undefined reference to log"... my includes look like this: (I'm using Eclipse on Ubuntu)
#include <stdio.h>
#include <stdlib.h>
#include "sample.h"
#include "graph_or.h"
#include <math.h>
and my makefile looks like this:
all:
gcc -g amostra.c sample.h -o amostra.o
gcc -g graph_or.c graph_or.h -o graph_or.o
gcc -g graph_w.c graph_W.h -o graph_W.o
gcc -g mutual_info.c -o mutual_info.o -lm
clean:
rm *.o
I have absolutely no idea what is going on, I have even tried to define the LDFLAGS before the command "all" and putting it like this:
LDFLAGS= -lm
all:
gcc -g amostra.c sample.h -o amostra.o
gcc -g graph_or.c graph_or.h -o graph_or.o
gcc -g graph_w.c graph_W.h -o graph_W.o
gcc -g mutual_info.c -o mutual_info.o -lm
clean:
rm *.o
But it still won't work!! Please anyone, I need help with this! Thanks!

Answer 1

Let's take this in steps.
The usual way to write a makefile is to have a rule for each target, and to use prerequisites:
thing: amostra.o graph_or.o graph_w.o mutual_info.o
gcc -g amostra.o graph_or.o graph_w.o mutual_info.o -o thing -lm
mutual_info.o: mutual_info.c
gcc -g -c mutual_info.c -o mutual_info.o -lm
amostra.o: amostra.c sample.h
gcc -g -c amostra.c -o amostra.o
graph_or.o: graph_or.c graph_or.h
gcc -g -c graph_or.c -o graph_or.o
graph_w.o: graph_w.c graph_w.h
gcc -g -c graph_w.c -o graph_w.o
mutual_info.o: mutual_info.c
gcc -g -c mutual_info.c -o mutual_info.o -lm
(I have guessed that you want the executable to be called thing, and that you meant graph_w, not graph_W.)
That should work, but we can make it tidier. First we introduce automatic variables:
thing: amostra.o graph_or.o graph_w.o mutual_info.o
gcc -g $^ -o $# -lm
mutual_info.o: mutual_info.c
gcc -g -c $< -o $#
amostra.o: amostra.c sample.h
gcc -g -c $< -o $#
graph_or.o: graph_or.c graph_or.h
gcc -g -c $< -o $#
graph_w.o: graph_w.c graph_w.h
gcc -g -c $< -o $#
mutual_info.o: mutual_info.c
gcc -g -c $< -o $#
Then we see that these recipes use the same command, so we create a pattern rule:
thing: amostra.o graph_or.o graph_w.o mutual_info.o
gcc -g $^ -o $# -lm
amostra.o: sample.h
graph_or.o: graph_or.h
graph_w.o: graph_w.h
%.o: %.c
gcc -g -c $< -o $#
Give this a try and tell us if it works.

Answer 2

Is that a snippet from your Makefile? Hav you tried exporting LDFLAGs? I have seen this error before, but it was always fixed with the -lm flag.
gcc -lm -o blah blah.c

Answer 3

you need to:
gcc -c -o amostra.o amostra.c
gcc -c -o graph_or.o graph_or.c
gcc -c -o graph_w.o graph_w.c
gcc -c -o mutual_info.o mutual_info.c
gcc -o YourExecutableName amostra.o graph_or.o graph_w.o mutual_info.o -lm

Answer 4

Here's a generic makefile using my best guess of what you want to achieve: It compiles all *.c files in the current directory and creates a binary mutual_info.
RM := rm -f
CC := gcc
CFLAGS := -g
LDLIBS := -lm
SOURCES := $(wildcard *.c)
OBJECTS := $(SOURCES:%.c=%.o)
DEPS := $(SOURCES:%.c=%.d)
BINARY := mutual_info
FILES_TO_CLEAN := $(OBJECTS) $(DEPS)
.PHONY : all clean realclean
all : $(BINARY)
clean :
$(RM) $(FILES_TO_CLEAN)
realclean : FILES_TO_CLEAN += $(BINARY)
realclean : clean
-include $(DEPS)
$(OBJECTS) : %.o : %.c
$(CC) $(CFLAGS) -c -MMD -o $# $<
$(BINARY) : $(OBJECTS)
$(CC) -o $# $^ $(LDLIBS)
Please clarify if that's not what you want.