HP C Programmer's Guide (92434-90009)

Chapter 5 121
Programming for Portability
5 Programming for Portability
The syntax of C is well defined as a result of the efforts of the ANSI X3J11 Technical
Committee. The standard C function libraries are rich with features that isolate programs
from operating system specific function calls. These factors make C programs highly
portable between various combinations of hardware platforms and operating systems.
The C programming language was first described in The C Programming Language, by
Brian Kernighan and Dennis Ritchie. This original language definition has proven
powerful enough to provide the functionality that programmers need. The HP C compiler
supports this language definition, including some Berkeley Software Distribution (BSD)
extensions.
S.C. Johnson developed the Portable C Compiler (pcc) that became available on a wide
range of systems, including the VAX and the HP 9000 Series 300/400 computers. The
syntax and semantics of HP C are closely compatible with those of pcc.
In December, 1989, the American National Standards Institute (ANSI) approved a
standard for the C programming language. The ANSI standard clarified a number of areas
that were ambiguous and tended to vary among C compilers. It gave full specifications for
the required library and codified a number of extensions that have been added to C over
the years. (ANSI mode first became available with release 7.0 on the Series 800, release
7.40 on Series 300/400, and release 8.05 on Series 700. Compatibility mode supports the C
syntax and semantics of previous releases.)
The ANSI standard specifies which aspects of C are required to work the same on
conforming implementations, and which can work differently. Since many
ANSI-conforming compilers are available on a wide variety of platforms, it is easy to
develop portable programs. HP C, when invoked in ANSI mode and used with the
preprocessor (cpp), headers, libraries, and linker, conforms fully with the standard.
Portable C programs are clear, reliable, and easily maintainable and can be easily
transported from one machine to another. With few modifications, C programs written
with portability in mind can be recompiled and run on different computers. For specific
information on system dependencies, refer to the HP C/HP-UX Reference Manual.
The ANSI C standard document American National Standard for Information Systems -
Programming Language C, ANSI/ISO 9899-1990 contains complete details on the
language including an appendix with a comprehensive list of portability issues. This
document is available from ANSI at 11 West 42nd Street, New York City, New York, 10036,
telephone [phone].
This chapter discusses some guidelines for making your C programs more portable.
Emphasis is placed on HP C specific portability issues, especially as they relate to porting
from pre-ANSI mode HP C (Kernighan and Ritchie plus BSD extensions) to ANSI mode
HP C.