How do I disable GCC optimization when using makefiles?

Question

I've just started learning Linux and I'm having some trouble disabling GCC's optimization for one of my C++ projects.

The project is built with makefiles like so...

make -j 10 && make install

I've read on various sites that the command to disable optimization is something along the lines of...

gcc -O0 <your code files>

Could someone please help me apply this to makefiles instead of individual code? I've been searching for hours and have come up empty handed.

Answer 1

In some standard makefile settings you could

make -j10 -e CPPFLAGS=-O0

But the makefile might use other substitution variables or override the environment. You need to show us the Makefile in order to propose edits

Answer 2

The simplest (useful) makefile that allows debug/release mode is:

#
# Define the source and object files for the executable
SRC     = $(wildcard *.cpp)
OBJ     = $(patsubst %.cpp,%.o, $(SRC))

#
# set up extra flags for explicitly setting mode
debug:      CXXFLAGS    += -g
release:    CXXFLAGS    += -O3

#
# Link all the objects into an executable.
all:    $(OBJ)
    $(CXX) -o example $(LDFLAGS) $(OBJ) $(LOADLIBES) $(LDLIBS)

#
# Though both modes just do a normal build.
debug:      all
release:    all

clean:
    rm $(OBJ)

Usage Default build (No specified optimizations)

> make
g++    -c -o p1.o p1.cpp
g++    -c -o p2.o p2.cpp
g++ -o example p1.o p2.o

Usage: Release build (uses -O3)

> make clean release
rm p1.o p2.o
g++ -O3   -c -o p1.o p1.cpp
g++ -O3   -c -o p2.o p2.cpp
g++ -o example p1.o p2.o

Usage: Debug build (uses -g)

> make clean debug
rm p1.o p2.o
g++ -g   -c -o p1.o p1.cpp
g++ -g   -c -o p2.o p2.cpp
g++ -o example p1.o p2.o