Trying to add a library to a make file - c++

Question

Hi this is my make file (I have very little make file experience sorry)
PROJECT_ROOT = $(dir $(abspath $(firstword $(MAKEFILE_LIST))))
OBJS = Angle.o \
AppControlTimer.o \
CableAngle.o \
CFunctionObject.o \
SonarDGCUArrayData.o \
SonarDGCUCommsTCP.o \
SonarDGCUEthernetClient.o \
SonarDGCUFinsPacket.o \
SonarDGCUMotorMemoryArea.o \
SonarDGCUSensorsData.o \
SonarDGCUSensorsMemoryArea.o \
SonarDGCUThread.o
LIB = libFins.a
INCPATH = ../../
INSTALL_DIR = /opt/s2193/lib64
ifeq ($(BUILD_MODE),debug)
CFLAGS += -g
else ifeq ($(BUILD_MODE),run)
CFLAGS += -O2
else ifeq ($(BUILD_MODE),linuxtools)
CFLAGS += -g -pg -fprofile-arcs -ftest-coverage
LDFLAGS += -pg -fprofile-arcs -ftest-coverage
else
$(error Build mode $(BUILD_MODE) not supported by this Makefile)
endif
CFLAGS += -MMD -Wall -Wextra -Wpedantic -Wno-vla
CFLAGS += -I$(PROJECT_ROOT)../target/nar/log4cxx-0.11.0.TUS1-noarch/include/ -c -Wall
CFLAGS += -I${INCPATH}include -DLINUX
LDFLAGS += -L$(PROJECT_ROOT)../target/libs/ -llog4cxx
CXXFLAGS += -DBUILD_WITHOUT_HAL -DDBG_LVL=7
CXX += -std=c++11
CC += -std=c11
.PHONY: all clean install
all: $(LIB)
$(LIB): $(OBJS)
$(AR) $(ARFLAGS) -o $# $^
%.o: $(PROJECT_ROOT)src/%.cpp
#echo ".cpp.o!! "$<
$(CXX) -c $(CFLAGS) $(CXXFLAGS) $(CPPFLAGS) -o $# $<
%.o: $(PROJECT_ROOT)src/%.c
#echo ".c.o!! $<"
$(CC) -c $(CFLAGS) $(CPPFLAGS) -o $# $<
clean:
rm -fr $(LIB) $(OBJS) $(OBJS:.o=.d)
install: $(LIB)
install -m 755 -d $(INSTALL_DIR)
install -m 644 $(LIB) $(INSTALL_DIR)
-include $(OBJS:.o=.d)
when I use the file I get undefined reflectances I'm trying to use the library
LDFLAGS += -L$(PROJECT_ROOT)../target/libs/ -llog4cxx
but I'm not sure how to add it to the file for reference when building libfins.a
thanks in advance

Answer 1

liblog4cxx supports pkg-config like any other sanely packaged library.
Stop writing flags by hand for libraries that you haven't made.
CXXFLAGS += $(shell pkg-config --cflags liblog4cxx)
LDFLAGS += $(shell pkg-config --libs liblog4cxx)
If you are really curious about flags your library needs, go ahead and run these two commands in your terminal, then leave it at that. Flags needed on your system are not necessarily flags needed on mine, that's why pkg-config exists, and people who made the library know better than you what it needs or does not need.
At the same time, pkg-config allows to expect a specific version of a library and all dependencies of your dependency are resolved transparently, without you having to do anything about it, and in fact you cannot do anything about it, because you don't know when or how the library or any of its dependencies will change, this becomes even more insane to manage yourself if you're linking statically. When using pkg-config, you just tack on --static and it gives you all the extra necessary flags.