Makefile not prompting compiler to use optimization flag - bash

Question

I have a simple makefile that I am using in bash to compile a C++ program and its associated .h files, not every .h file has a .cpp file associated with it. I wrote a makefile where each dependency was called out explicitly and the CFLAG macro was used for each specific dependency and it did compile with the -O3 flag and ran nearly 3 times faster. However, when I use this simpler, but somewhat more sophisticated makefile, it does not compile with the -O3 flag even though it is clearly included with the CFLAG macro. Can someone point out to me what I am missing, I would greatly appreciate it.
OBJS = main.o Output_Files.o Calendar.o Random_Number_Generator.o \
Algorithm.o Statistics.o
DEPS = Output_Files.h Calendar.h Random_Number_Generator.h Algorithm.h \
Statistics.h
CC=c++
CFLAGS=-c -Wall -O3
all: economics
%o: %.cpp $(DEPS)
$(CC) $(CFLAGS) $# $<
economics: $(OBJS)
$(CC) $(OBJS)
main.o: main.cpp Data_Parser.h PDF_and_CDF.h
$(CC) $(CFLAGS) main.cpp

Answer 1

The rule:
%o: %.cpp $(DEPS)
$(CC) $(CFLAGS) $# $<
should be written with an extra dot:
%.o: %.cpp $(DEPS)
$(CC) $(CFLAGS) $<
Also, you don't want $# in the command line, or (if you must have it) you need to prefix it with -o.
The makefile is not using the faulty rule but instead uses the default rule for building C++ object files, and that most probably doesn't use $(CFLAGS) but uses $(CXXFLAGS) instead.
CC is the macro for the C compiler, not the C++ compiler. Normally, that is CXX. Also, the rule to build economics actually creates a.out and not economics.
I'd prefer it if you wrote:
SRCS = main.cpp Output_Files.cpp Calendar.cpp Random_Number_Generator.cpp \
Algorithm.cpp Statistics.cpp
OBJS = ${SRCS:.cpp=.o}
…
economics: $(OBJS)
$(CC) -o $# $(OBJS)
Putting it all together gives this new.makefile:
SRCS = main.cpp Output_Files.cpp Calendar.cpp Random_Number_Generator.cpp \
Algorithm.cpp Statistics.cpp
OBJS = ${SRCS:.cpp=.o}
DEPS = Output_Files.h Calendar.h Random_Number_Generator.h Algorithm.h \
Statistics.h
CC = c++
CFLAGS = -c -Wall -O3
all: economics
%.o: %.cpp $(DEPS)
$(CC) $(CFLAGS) $<
economics: $(OBJS)
$(CC) -o $# $(OBJS)
main.o: main.cpp Data_Parser.h PDF_and_CDF.h
$(CC) $(CFLAGS) main.cpp
Running make -n with the old makefile
$ make -n -f old.makefile
c++ -c -Wall -O3 main.cpp
c++ -c -o Output_Files.o Output_Files.cpp
c++ -c -o Calendar.o Calendar.cpp
c++ -c -o Random_Number_Generator.o Random_Number_Generator.cpp
c++ -c -o Algorithm.o Algorithm.cpp
c++ -c -o Statistics.o Statistics.cpp
c++ -o economics main.o Output_Files.o Calendar.o Random_Number_Generator.o Algorithm.o Statistics.o
$
Running make -n with the new makefile
$ make -n -f new.makefile
c++ -c -Wall -O3 main.cpp
c++ -c -Wall -O3 Output_Files.cpp
c++ -c -Wall -O3 Calendar.cpp
c++ -c -Wall -O3 Random_Number_Generator.cpp
c++ -c -Wall -O3 Algorithm.cpp
c++ -c -Wall -O3 Statistics.cpp
c++ -o economics main.o Output_Files.o Calendar.o Random_Number_Generator.o Algorithm.o Statistics.o
$
This is still an abnormal way of writing the make rules on a number of grounds, one being the $(CC) vs $(CXX) change. Normally, the -c option is not included in $(CFLAGS) or $(CXXFLAGS). Normally, you include $(CFLAGS) or $(CXXFLAGS) in the link line too (because some of the flags might affect linking). Often, you need libraries and related flags in the linker line too.
This leads to a more orthodox naming convention:
SRCS = main.cpp Output_Files.cpp Calendar.cpp Random_Number_Generator.cpp \
Algorithm.cpp Statistics.cpp
OBJS = ${SRCS:.cpp=.o}
DEPS = Output_Files.h Calendar.h Random_Number_Generator.h Algorithm.h \
Statistics.h
CXX = c++
CXXFLAGS = -Wall -O3
LDFLAGS =
LDLIBS =
all: economics
%.o: %.cpp $(DEPS)
$(CXX) -c $(CXXFLAGS) $<
economics: $(OBJS)
$(CXX) -o $# $(CXXFLAGS) $(OBJS) $(LDFLAGS) $(LDLIBS)
main.o: main.cpp Data_Parser.h PDF_and_CDF.h
$(CXX) -c $(CXXFLAGS) main.cpp