User`s guide

Compiler Overview [7]
In separate-module mode, the .o files are true object files. The compiler optimizes
each object file, or module, separate from the others. The link step produces a
program library, although this program library primarily contains information that
directs the debugger to various object files.
Because of the relative sizes of the .o files in the two compilation modes, the
qualifier skinny refers to whole-program mode and its products (such as the .o files)
and the qualifier fat refers to separate-module mode and its products.
During the compilation process, the compiler creates the following files:
a.out The executable file.
a.out.pl The program library.
LOCK.a.out.pl
The temporary lock file. The lock file prevents other compilers from
accessing a program library when it is already in use. The compiler
removes this file after use, unless the compiler terminates before
completion.
*.o Relocatable object files.
7.1.1 File Types Accepted by the Compiler
The compiler accepts files that use the following extensions:
.c C file when invoked with cc, C++ file when invoked with c++.
.cc, .cpp C++ file.
.o In whole-program compilation, time stamp file that does not need
to be compiled but participates in any link step. Also referred to as
a skinny .o file. In separate-module compilation, a true object file.
Also referred to as a fat .o file.
.pl Program library. Used to support incremental recompiling and
debugging. In whole-program compilation, used to support
inter-module analysis.
.a Archive or library file.
File prefixes used in the compilation process include the following:
LOCK Temporary lock file used to prevent concurrent updates to the
associated program library.
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