Add a source directory to a Makefile - c++

Question

I have the following makefile:
CPP_COMPILER = g++
CPP_COMPILER_FLAGS = -g -O0 -Wall -Wextra -Wpedantic -Wconversion -std=c++17
EXECUTABLE_NAME = mainDebug
CPP_COMPILER_CALL = $(CPP_COMPILER) $(CPP_COMPILER_FLAGS)
INCLUDE_DIR = include
SOURCE_DIR = src1
BUILD_DIR = build
CPP_SOURCES = $(wildcard $(SOURCE_DIR)/*.cpp)
CPP_OBJECTS = $(patsubst $(SOURCE_DIR)/%.cpp, $(BUILD_DIR)/%.o, $(CPP_SOURCES))
build: $(BUILD_DIR)/$(EXECUTABLE_NAME)
TARGET_DEPS = $(CPP_OBJECTS)
$(BUILD_DIR)/$(EXECUTABLE_NAME): $(TARGET_DEPS)
$(CPP_COMPILER_CALL) $^ -o $#
execute:
.$(BUILD_DIR)/$(EXECUTABLE_NAME)
$(BUILD_DIR)/%.o: $(SOURCE_DIR)/%.cpp
$(CPP_COMPILER_CALL) -I $(INCLUDE_DIR) -c $< -o $#
clean:
rm -rf $(BUILD_DIR)/*.o $(BUILD_DIR)/$(EXECUTABLE_NAME)
And the following folder structure:
.
├── build
├── include
│ ├── mylib.h
│ └── test.h
├── Makefile
├── src1
│ ├── main.cc
│ └── mylib.cc
└── src2
└── test.cc
This works correctly with src1 but when adding src2 to SOURCE_DIR,
SOURCE_DIR = src1\
src2
I get the following error:
/usr/bin/ld: cannot find src1: file format not recognized
collect2: error: ld returned 1 exit status
make: *** [Makefile:22: build/mainDebug] Error 1
What am I doing wrong here ?

Answer 1

Look at how you use SOURCE_DIR:
SOURCE_DIR = src1
...
CPP_SOURCES = $(wildcard $(SOURCE_DIR)/*.cpp)
CPP_OBJECTS = $(patsubst $(SOURCE_DIR)/%.cpp, $(BUILD_DIR)/%.o, $(CPP_SOURCES))
...
$(BUILD_DIR)/%.o: $(SOURCE_DIR)/%.cpp
$(CPP_COMPILER_CALL) -I $(INCLUDE_DIR) -c $< -o $#
After you define it, you use it three times, each time as a single directory name. You cannot simply add a second name to the variable and expect Make to iterate properly over the list.
First, use addsuffix to get the right pattern for wildcard:
CPP_SOURCES = $(wildcard $(addsuffix /*.cpp,$(SOURCE_DIR)))
Then use CPP_SOURCES instead of SOURCE_DIR:
CPP_OBJECTS = $(patsubst %.cpp, $(BUILD_DIR)/%.o, $(notdir $(CPP_SOURCES)))
Then use vpath to find the sources:
vpath %.cpp $(SOURCE_DIR)
$(BUILD_DIR)/%.o: %.cpp
$(CPP_COMPILER_CALL) -I $(INCLUDE_DIR) -c $< -o $#