User's Guide

4 Preprocessing Directives
HP aC++ has its own, internal, preprocessor which is similar to the HP C preprocessor described
in the HP C/HP-UX Reference Manual. When you issue the aCC command, your source files are
automatically preprocessed.
This Chapter discusses the following topics:
• “Overview of the Preprocessor” (page 119)
• “Syntax” (page 119)
• “Usage Guidelines” (page 119)
• “Source File Inclusion (#include, #include_next)” (page 120)
• “Macro Replacement (#define, #undef)” (page 121)
• “Assertions (#assert, #unassert)” (page 125)
• “Conditional Compilation (#if, #ifdef, .. #endif)” (page 126)
• “Line Control (#line)” (page 128)
• “IOSTREAM Performance Improvement Pragma” (page 129)
• “Pragma Directive (#pragma) and _Pragma Operator” (page 129)
• “Error Directive (#error)” (page 130)
• “Warning Directive” (page 130)
• “Trigraph Sequences” (page 130)
Overview of the Preprocessor
A preprocessor is a text-processing program that manipulates the text within your source file. You
enter preprocessing directives into your source file to direct the preprocessor to perform certain
actions on the source file. For example, the preprocessor can replace tokens in the text, insert the
contents of other files into the source file, or suppress the compilation of part of the file by
conditionally removing sections of the text. It also expands preprocessor macros and conditionally
strips out comments.
Syntax
The general syntax for a preprocessor directive is:
preprocessor-directive ::=
include-directive newline
macro-directive newline
conditional-directive newline
line-directive newline
pragma-directive newline
error-directive newline
trigraph-directive newline
warning-directive newline
Usage Guidelines
Following are rules and guidelines for using preprocessor directives:
• A preprocessor directive must be preceeded by a pound sign (#). White-space characters
may precede the # character.
• The # character is followed by any number of spaces and horizontal tab characters and a
preprocessor directive.
Overview of the Preprocessor 119