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

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.

Answer 1

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

Answer 2

$(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