C Compilation

Source codes for C programs are written as ASCII text. They must be compiled and linked to produce executable programs. The executable files are what you actually run on UNIX.

The compilation of code involves several steps:

parsing of the statements for syntax
translation of the statements into machine language
setting up the addresses of all variables
optimization of the code (if desired)

In most modern computers, various languages, e.g. Fortran and C, have distinct syntax handlers, but share a common translator into assembly language, and a common optimization engine.

The linking step assembles the various routines produced by the compiler during the compilation step, and resolves missing calls to either language-specific libraries or system-wide functions.

We will use the GNU C compiler for this course because it is (a) free and (b) more efficient than the Sun equivalent. This compiler is invoked via the gcc command. Typing

	gcc fname.c

will compile the file fname.c, linked it to the default libraries and produce an executable file called by default a.out.

Several parameters may be used to modify the default in the compilation. Some of these are:

	-o out_file        specify the output file (executable, or
	                   binary) to be out_file

	-O, -O1, -O2, -O3  specify optimization level

	-c fname.c         indicates that you only want to compile
			   the file fname.c, in which case
	                   the output file will be fname.o

	-lname             links with the library libname.a

	-Ldirectory        directs gcc to look for libraries in
	                   directory, in addition to the
	                   standard system library path

We strongly advise that you omit optimization until you are sure a program works. Optimizers tend to change the code around internally for the sake of efficiency, and they can make it extremely difficult to find errors in a complicated program. In addition, many have been known to introduce bugs of their own...

We also maintain the following aliases on newton to facilitate your compilations:


	C fname    will compile and link the C program in
		   the file fname.c with the standard
		   C mathematics library, placing the executable
		   in fname

        Cgfx       will compile the code in fname.c,
		   then link it with the standard C mathematics
		   library and the xutility graphics
		   library.

                   This library contains (among other things)
		   a set of plotting functions written by Biao
		   Lu (a former graduate student who left us
		   in 1994) which form the basis for much of
		   the graphics we will need to do during the
		   quarter.