make objects in Makefile - c++

Question

I have the following Makefile:
CXX = g++
CXXFLAGS = -Wall -g
SOURCES := divisor.cpp multiplier.cpp
OBJECTS := ${SOURCES:.cpp=.o}
%.o: %.cpp
$(CXX) -c $(CXXFLAGS) $< -o $#
%: %.o $(OBJECTS)
$(CXX) $(CXXFLAGS) $#.o -o $#.out
$(OBJECTS): %.o: %.cpp
$(CXX) -c $(CXXFLAGS) $< -o $#
clean:
rm -f *.o
What I want this make file is the following:
If I add a source file called 123.cpp to the working directory, I want it to generate its object file and then link the compiled sources specified in $(SOURCES), this means:
g++ -c -Wall -g 123.cpp
g++ multipler.o divisor.o 123.o -o 123
If multiplier.cpp or divisor.cpp has to be generated or updated, I want make to do it.
But I'm failing, because divisor.o and multiplier.o are not automatically generated
How may I achieve this?
Edit
Just to clarify, there are two types of source code files in the working directory: divisor.cpp, multipler.cpp is one type, and any other file, say, 123.cpp is the other type. In a sense, divisor.cpp and multiplier.cpp are requisites to the other source files.
I want to automate the process of compiling the prerequisites and link them when compiling the other files
g++ -c multiplier.cpp
g++ -c divisor.cpp
g++ -c -Wall -g 123.cpp
g++ multipler.o divisor.o 123.o -o 123

Answer 1

Use the wildcard function:
SOURCES := $(wildcard *.cpp)
Then, you can remove your "special" source files:
SPECIAL_SOURCES := divisor.cpp multiplier.cpp
SOURCES := $(filter-out $(SPECIAL_SOURCES),$(SOURCES))
And change your rules to build the stuff you actually want:
$(SPECIAL_OBJECTS) := $(SPECIAL_SOURCES:.cpp=.o)
$(BINARIES) := $(patsubst .cpp,,$(SOURCES))
$(SPECIAL_OBJECTS) : %.o : %.cpp
$(CXX) $(CXXFLAGS) -c -o $# $^
$(BINARIES) : % : %.cpp $(SPECIAL_OBJECTS)
$(CXX) $(CXXFLAGS) -o $# $^