How to add compile flag -g to a make file? - c++

Question

I got a C++ program for which someone else made a make file. I want to compile the program with flag -g, but I don't know where to add it. Below is the make file.
CC = g++
LOADLIBES = -lm
CFLAGS = -Wall -O2
SRC1 = Agent.cpp Breeder.cpp CandidateSolution.cpp \
Cupid.cpp FateAgent.cpp Grid.cpp Reaper.cpp \
fitness.cpp
SRC2 = main.cpp
SRC = $(SRC1) $(SRC2)
OBJS = $(SRC1:.cpp = .o)
AUX = $(SRC1:.c = .h)
main: $(OBJS)
# $(CC) $(CFLAGS) -o $(SRC) $(AUX)
.PHONY: clean
clean:
rm -f *.o main
Where should I add that I want to use -g?

Answer 1

$(CC) is used for compiling C programs. $(CXX) is used for compiling C++ programs. Similarly $(CFLAGS) is used for C programs, $(CXXFLAGS) is used for compiling C++.
Change the first few lines to this:
#CC = g++
LOADLIBES = -lm
CXXFLAGS = -Wall -O2 -g
(But see others' notes about incompatibilities between -O2 and -g.)
Get rid of the spaces inside the parentheses in this line:
OBJS = $(SRC1:.cpp=.o)
Change the main lines to this:
main: $(OBJS) $(SRC2)
# Built by implicit rules
The resulting makefile should look like this:
#CC = g++
LOADLIBES = -lm
CXXFLAGS = -Wall -O2 -g
SRC1 = Agent.cpp Breeder.cpp CandidateSolution.cpp \
Cupid.cpp FateAgent.cpp Grid.cpp Reaper.cpp \
fitness.cpp
SRC2 = main.cpp
SRC = $(SRC1) $(SRC2)
OBJS = $(SRC1:.cpp=.o)
AUX = $(SRC1:.c=.h)
main: $(OBJS) $(SRC2)
# Built by implicit rules
.PHONY: clean
clean:
rm -f *.o main
and the output should look like this:
$ make
g++ -Wall -O2 -g -c -o Agent.o Agent.cpp
g++ -Wall -O2 -g -c -o Breeder.o Breeder.cpp
g++ -Wall -O2 -g -c -o CandidateSolution.o CandidateSolution.cpp
g++ -Wall -O2 -g -c -o Cupid.o Cupid.cpp
g++ -Wall -O2 -g -c -o FateAgent.o FateAgent.cpp
g++ -Wall -O2 -g -c -o Grid.o Grid.cpp
g++ -Wall -O2 -g -c -o Reaper.o Reaper.cpp
g++ -Wall -O2 -g -c -o fitness.o fitness.cpp
g++ -Wall -O2 -g main.cpp Agent.o Breeder.o CandidateSolution.o Cupid.o FateAgent.o Grid.o Reaper.o fitness.o -lm -o main
For completeness, this is the version of make I am using on Ubuntu 10.04:
$ make -v
GNU Make 3.81
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
This program built for i486-pc-linux-gnu

Answer 2

You need to uncomment the line:
# $(CC) $(CFLAGS) -o $(SRC) $(AUX)
(remove the hash sigh):
$(CC) $(CFLAGS) -o $(SRC) $(AUX)
And change
CFLAGS = -Wall -O2
to
CFLAGS = -Wall -O2 -g
But you may find debugging easier if you disable optimization by removing -O2:
CFLAGS = -Wall -g