adding a dir to the search path

["Fred J." <phddas@yahoo.com>]

Hi
I am trying to link the gsl library to my c++ project. using debian/testing 2.5.16 and g++ 4.0.3-4
the instruction in the library is:
If the directory is not installed on the standard search path of your compiler you will also need to provide its location to the preprocessor as a command line flag.

$g++ -print-search-dirs 
ok, it is not here
I google and search the man pages but could not do it.

please tell me how to:
1) add it to my compiler search path.
2) provide its location to the preprocessor in the makefile below

thanks alot

OBJS = read_data.o read_data_test.o
COMP = g++

#### linker section ####
proj: $(OBJS)
    $(COMP) $(OBJS) -o proj
########################


#### compiler section ####
.SUFFIXES:.o .cpp .h
.h.o:
    $(COMP) -c $<
##########################

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