usinggsl.txt

I figured out how to use the GSL libraries once and don't want to do it again, so here are some instructions.
Note: these instructions should apply with obvious modifications to other libraries.

First, assume you have a file with C code in it that uses a function from GSL.
Then you'll have the include statment in the file:

#include <gsl/header.h>

Where header.h is the particular header file with the particular function you need.
Lets assume the file is called file.c. Then compiling and linking is done in two
separate steps. First, run

gcc -Wall -I/apps/include file.c -c

-Wall is for error control and not necessary for compiling to work. 
-Idirectory just gives the directory of the gsl header files since they aren't in the compiler's path.
	    In this case, /apps/include is that directory.
file.c is the name of the file containing the C code.
-c tells the compiler not to link - this will be done in a discrete second step.
The output, by default, is an object file: file.o.

Now for the linking step. 

gcc -L/apps/lib file.o -lgsl -lgslcblas -lm -o file_c.out

-Ldirectory just gives the directory of the gsl libraries since they aren't in the compiler's path.
file.o is the name of the object file from the previous step.
-llibraryname or equivalently -l libraryname tells the compiler to search the library named "libraryname"
	      when linking. In this case, it's searching the gsl, gslcblas, and m libraries. (The "m" 
	      library is the system math library.) Note that order of the .o file and the libraries affects 
	      the output: it searches from left to right.
-o file_c.out just tells the compiler what to name the output file. This file can be run with ./file_c.out