How to include from directory? - compilation

Question

I am trying to add a project's (call it b) code to a different project(call it a). Both projects are compile and run separately. I just copied the folder of project b into project a's folder. In project a's Makefile, I added the lines to compile project b with it. It compiles fine. Now I want to use b's code. But when I try to #include "/bfolder/somefile.h", it cannot find the file. What am I missing about this? If I can just #include "somefileinsamedirectory.h", why can't I do #include "/bfolder/somefile.h"?`
This is a 's Makefile that I have edited to include the irobot_driver code.
INCLUDE = -I/usr/X11R6/include -I/home/sterling/irobot_driver
CC=g++
CFLAGS=-w -D LINUX -fpermissive
CFLAGS_R= -w -D LINUX -O3 -fpermissive
CFLAGS_D=-w -D LINUX -fpermissive
OBJ= obj
OBJ_DEBUG= obj_debug
OBJDIR= release
SRCDIR= src
LDFLAGS= -L/usr/X11R6/lib$(LIBSELECT) -lGL -lfltk -lfltk_gl -lXext -lX11 -lglut -lGLU -lfltk_images
SOURCES_RAW=codeprofiler.cpp gametimer.cpp timer.cpp timeprofile.cpp vector4.cpp matrix.cpp agent.cpp agentcontroller.cpp dummy.cpp evader.cpp pursuer.cpp goal.cpp player.cpp graphdata.cpp graph.cpp cubiccoefs.cpp segment.cpp trajectory.cpp anode.cpp arrayvector4.cpp color.cpp drawcomponent.cpp drawcontroller.cpp flags.cpp global.cpp map_analyzer.cpp minheap.cpp node.cpp quadtree.cpp queue.cpp results.cpp sensor.cpp settings.cpp utility.cpp world.cpp gui.cpp main.cpp logger.cpp parameters.cpp counter.cpp polygon.cpp line.cpp
TARGET:= pursuit_evasion
TARGETD:= pursuit_evasion_d
TARGETP:= pursuit_evasion_p
TARGETW32:= pursuit_evasion_w32
OBJECTS:=$(SOURCES_RAW:.cpp=.o)
OBJECTS:=$(patsubst %.o,$(OBJDIR)/%.o, $(OBJECTS))
SOURCES:=$(SOURCES_RAW)
SOURCES:=$(patsubst %.cpp,$(SRCDIR)/%.cpp, $(SOURCES))
OBJ_DEBUG:=$(SOURCES_RAW:.cpp=.o)
OBJ_DEBUG:=$(patsubst %.o,debug/%.o, $(OBJ_DEBUG))
OBJECTS_P:=$(SOURCES_RAW:.cpp=.o)
OBJECTS_P:=$(patsubst %.o,profile/%.o, $(OBJECTS_P))
OBJDIR=obj
all: $(TARGET)
#--- Release
$(TARGET): $(OBJECTS)
$(CC) -w -D LINUX $(INCLUDE) $^ -o $# $(LDFLAGS)
cd /home/sterling/irobot_driver; sudo make -j2
release/%.o: src/%.cpp
$(CC) -c $< $(CFLAGS_R) -o $#
#--- Debug
debug: $(TARGETD)
$(TARGETD): $(OBJ_DEBUG)
$(CC) -w -D LINUX $(INCLUDE) $^ -o $# $(LDFLAGS)
cd /home/sterling/irobot_driver; sudo make -j2
debug/%.o: src/%.cpp
$(CC) -c -g $< $(CFLAGS)-o $#
#-- Profile
profile: $(TARGETP)
$(TARGETP): $(OBJECTS_P)
$(CC) -w -g -pg -D LINUX $(INCLUDE) $^ -o $# $(LDFLAGS)
profile/%.o: src/%.cpp
$(CC) -c -g -pg $< $(CFLAGS)-o $#
win32: $(TARGETW32)
$(TARGETW32): $(OBJECTS)
$(CC) -w -D WIN32 $(INCLUDE_W32) $^ -o $# $(LDFLAGS)
.PHONY : clean
clean:
rm -f release/*.o
rm -f debug/*.o
rm -f profile/*.o
rm -f $(TARGET) $(TARGETD) $(TARGETP)
cd /home/sterling/irobot_driver; make clean;
The #include "/the/whole/path/to/a/file" that works is -
#include "/home/sterling/irobot_driver/robot_driver_agent.h"

Answer 1

You can, but when you declare the path starting with /some/path/to/file.h it's going to really look for the file at /some/path/to/file.h. If instead you want the bfolder/somefile.h, remove the / from the beginning.
Also, in general, if b is a library that you want to use, it is best to keep it in whatever folder it resides, and include and link using the -I, -L and -l options of gcc, or similar options of other compilers. This way, if you update b you don't need to copy it to every project that uses it.

Answer 2

Try
#include "bfolder/somefile.h"
You are including a leading slash in "/bfolder/somefile.h", which means /bfolder would be in the root directory.

Answer 3

#include "/bfolder/..." would be implying that bfolder is in the root directory of your computer's file system. If bfolder is in the same directory as your source code, then you would just want #include "bfolder/somefile.h"