Question

I have the following makefile

CXX       = g++
CXXFLAGS  = -c -g -pg -Wall -Wextra
LINK      = g++
TARGET    = ../../Binaries/tests
SOURCES   := ../Src/$(wildcard *.cpp)
OBJS_DIR  := ../Objects
OBJS      = $(sort $(patsubst %.cpp, $(OBJS_DIR)/%.o, $(patsubst %.c, $(OBJS_DIR)/%.o, $(notdir $(SOURCES)))))

tests: $(TARGET)

$(TARGET): $(OBJS)
  $(LINK) $? -o $@

$(OBJS): $(SOURCES)
  $(CXX) $(CXXFLAGS) $? -o $@

which, when run using make tests (or simply just make), gives the following output:

g++  -o ../../Binaries/tests
g++: fatal error: no input files
compilation terminated.
make: *** [../../Binaries/tests] Error 4

This seems to me that make is trying to link the files (that don’t yet exist) without checking the rule for $(OBJS). My goal is to have a Makefile that is entirely self sufficient, being able to find the *.cpp file in ../Src and the *.o file (that it will generate itsef) in ../Objects, however the rule I’ve written doesn’t seem to be working out that way. Can anyone please tell me where I’ve gone wrong here?

Answer 1

Most likely, the problem is on the following line:

SOURCES   := ../Src/$(wildcard *.cpp)

It should be something like this instead:

SOURCES   := $(wildcard ../Src/*.cpp)

Also transforming sources into objects could be rewritten as follows:

OBJS      := $(SOURCES:../Src/%.cpp=$(OBJS_DIR)/%.o)

Finally the compilation rule is usually implemented through pattern rules:

$(OBJS_DIR)/%.o : ../Src/%.cpp
    $(CXX) $(CXXFLAGS) $< -o $@