C language compilers

Compilation modes

The compilation system has four compilation modes that correspond to degrees of compliance with ANSI C. The modes are:

ANSI C mode. Specifies standards conformance except that some required warnings are omitted and the name space is expanded to include names that are not specified by the standards. All C constructions behave as specified in the standards. All implemented language and library extensions beyond the standards are also available. This is the default.

Backward compatibility mode. Like -Xa, except that restrict and inline are not taken as C99 keywords.

Conformance mode. Specifies strict standards conformance. Since the name space of the language and headers are reduced from that of -Xa, certain extensions, such as the asm keyword, and some commonly expected header file declarations are not available.

Transition mode. Specifies standards conformance except where the semantics differ from classic C. Under this option, the compiler provides new ANSI C features and supports all extensions that were provided in C Issue 4 (CI4), which was the release made available
with System V Release 3. Where the interpretation of a construct differs between CI4 and the Standard, the compiler issues a warning and follows the CI4 behavior.

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