Installation guide

• The DIGITAL UNIX C compiler supports only predefined macros that
begin with two underscore characters (__) when you use the −std
option. Macro names that do not begin with two underscore characters
are valid when you use the default compilation mode of the DEC C
compiler.
• The DIGITAL UNIX C compiler does not support the VAX C (vcc)
compatibility mode keywords, language interpretations, or extensions.
See Section 7.4.5 for information about differences between the (vcc)
compiler and the DIGITAL UNIX cc compiler.
• The DIGITAL UNIX C compiler does not support the −check option for
checking code similar to the way the lint command checks it. To check
your DIGITAL UNIX C code, use the lint command as described in
lint
(1).
• The DIGITAL UNIX C compiler does not support the
−source_listing or −show options for displaying source code listing
and intermediate and final macro expansions.
7.4.4 Differences Between DIGITAL UNIX C and C on VAX Systems
If you compile an application you wrote for the cc compiler on VAX
ULTRIX systems with the DIGITAL UNIX C compiler, you might notice
some differences in the language definitions the compilers accept. Some of
these differences are hardware specific, others are differences in how the
compilers are implemented.
To minimize the effect of these differences, use the DIGITAL UNIX C
compiler option that offers the most compatibility, as shown in Table 7–5.
Table 7–5: Compilation Option that Is Compatible with C on VAX Systems
If You Use This ULTRIX Option Use This DIGITAL UNIX Option
Default (K&R C) Default (−std0)—K&R C with ANSI extensions.
Some differences exist due to differences
between VAX and RISC systems and differences
between the compilers.
The following list details the differences between the DIGITAL UNIX C
compiler when you use the −std0 option and the cc command on a VAX
machine:
• The pointers on RISC systems are unsigned; on VAX systems they are
signed.
• On RISC systems, you cannot dereference NULL pointers, including
arguments to the strlen function.
Migrating Your ULTRIX Application to a DIGITAL UNIX System 7–29