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Date: Mon, 8 Mar 93 16:22:00 -0500
From: mccorkle@oasis1 (Sean McCorkle)
Message-Id: <9303082122.AA07181@oasis1.phy.bnl.gov>
To: nepsee
Subject: How to get started with C page
Status: RO


Essentials
----------

    C programs are usually both compiled *and* linked with the cc command.
Although unix does not have a file type or extension field, the compiler
recognizes the suffix .c to indicate a C source file, and .o to indicate
an object file.  Executable (or binary) files generally do not have a suffix.

    A typical command to compile and link the main program prog.c and its
associated subroutines may look like this:

            cc -o prog  prog.c  sub1.c  sub2.o  sub3.c

The "-o prog" instructs the compiler to call the executable file "prog".  If
this is not specified, the name "a.out" will be used (this is an historical
idiosyncracy).  The compiler looks at the suffix of the subsequent arguments
and will compile .c files, producing .o files (which are erased after linking)
and linking them with any .o files specified.

    Often, it is desirable to only compile a .c file without linking.
This is accomplished with the -c option:

            cc -c  prog.c 

This produces the object file prog.o which may be linked at a later in
this way:

            cc -c  prog.o  sub1.c  sub2.o  sub3.c


    Note that although the linking can be accomplished manually with
the unix loader "ld",  almost nobody does it this way, since cc does this
for you.


More Suffix Types
-----------------

In addition to .c and .o, cc recognizes .s to be an assembly source file,
.a to be a library archive, .f to be a fortran program (in which case f77
.s invoked to produce a .o file), .i to be C source file produced by running
the C preprocessor on it.   CC can also produce ucode object files, with the
extension .u if you specify the -j option.


Using Libraries
---------------

In addition to linking with user created archive libraries (.a files) a user
may also link with one of the many system libraries with the -l option.
By specifing -labc on the cc command, the compiler will link with the system
library libabc.a;  this will be searched for in the directories /lib,
/usr/lib and /usr/local/lib.  You can have additional directories searched
by specifing -L "dir" before any -l options.

Important libraries which are not searched by default include -lm (the
math library: cos(), exp(), tan(), etc) and -LX11 (the X11 library).


Other Useful Options
--------------------

#include files are searched for in the source file's directory first, 
and then in the standard directory /usr/include.  You can suppress this
by specifying -I  or you can add additional directories to be seached 
by specifying -Idir.

The -P option runs only the preprocessor on each source file and puts
the output in .i files.  This is useful if you have problems with macros.


For Additional Information
--------------------------

            man cc     -  C compiler documentation
            man ld     -  loader (linker) documentation
            man "func" -  documentation on library function "func"
                          ( i.e,  man cos  or   man exp )