5 Preprocessor Directives

The DEC C preprocessor provides the ability to perform macro substitution, conditional compilation, and inclusion of named files. Preprocessor directives, lines beginning with # and possibly preceded by white space, are used to communicate with the preprocessor. The DEC C Language Reference Manual describes the ANSI-compliant preprocessor directives available with the DEC C compiler. This chapter describes the preprocessor directives that are either specific to DEC C on OpenVMS systems, or that are used in an implementation-specific way:

• The #dictionary directive, used for CDD/Repository extraction (Section 5.4.2, Section 5.1)

• The #include directive, used for file inclusion (Section 5.2)

• The #module directive, for specifying an alternative name and identification for the object module (Section 5.3, Section 5.4.11)

• The #pragma directive and pragmas specific to OpenVMS systems (Section 5.4)

If you plan to port programs to and from other C implementations, take care in choosing which preprocessor directives to use within your programs. See the DEC C Language Reference Manual for more information about using preprocessor directives for conditional compilation. For a complete discussion of portability concerns, see the DEC C Run-Time Library Reference Manual for OpenVMS Systems.

Preprocessor directives are independent of the usual scope rules; they remain in effect from their occurrence until the end of the compilation unit. For more information about the compilation unit, see Chapter 1.