HP 3000 Manuals HP 3000 Manuals
HP C/XL Enhancements by Erryl Johnson Systems Technology Division The HP C/XL compiler, preprocessor, header files, and libraries are enhanced to provide complete conformance to the ANSI standard for the C language, X3.159-1989. A new compiler option, -Aa, allows the programmer to enable ANSI mode. With ANSI mode enabled by the -Aa option, the compiler accepts a number of new language features, many of which are designed to make C a safer language, but without diminishing the freedom which has traditionally been available to the C programmer. It does more thorough error checking, with the result that more bugs will be detected at compile time rather than run time. It also promotes portability by guaranteeing standard handling of certain language features which have frequently been trouble spots, such as macro expansion and integral promotion rules. Another new compiler option, -Ac (the default), is provided for programs which rely on certain nonstandard behaviors of pre-ANSI compilers or preprocessors, including previous releases of HP C. This option allows existing programs which compiled without warning on previous releases of HP C/XL to continue to compile and execute properly. ANSI is the recommended mode of compilation. Many (if not most) existing programs will compile and execute properly under ANSI C with no changes. Unless you need to port your code to a system where an ANSI C compiler is not yet available, it is suggested that you use ANSI mode whenever you need to recompile existing programs. If you would like to override the current default and make ANSI mode the default, you may do so by establishing a CCOPTS CI variable containing the -Aa option (:SETVAR CCOPTS "-Aa"). NEW HP C/XL ANSI FEATURES Following is a partial list of the new features available to the programmer in ANSI mode: Function prototypes provide a means of specifying the number of parameters to a function and the type of each parameter. On calls to the function, the arguments will be checked for compatibility with the parameters, and automatic conversions will be performed where appropriate. The program's namespace is protected. ANSI C provides a well defined list of reserved words, with the guarantee that all other identifiers can be safely used by the programmer. Multicharacter constants, such as 'xyz', are accepted. Concatenation of string literals is supported. The adjacent tokens "abc" and "pqr", even if on separate lines and separated by a comment, will be joined into a single token "abcpqr". The preprocessor supports the new directives #error and #elif, as well as the # and ## operators. Directives can be indented. Compilation date and time are available with the macros __DATE__ and __TIME__. The type qualifiers const and volatile are fully supported. The suffixes "U" (unsigned) and "F" (float) are permitted in arithmetic constants. Automatic arrays and structures can be initialized. Unions can be initialized. Unions can contain bit-fields. The data type "long double" provides 128-bit floating-point arithmetic. Values with type "float" are not promoted automatically to "double". Trigraphs provide a way of representing the basic C character set on non-ASCII terminals and printers. Internationalization is supported by wide character constants, wide string literals, and standard library routines for manipulating strings of multibyte characters and wide characters. OTHER NEW FEATURES Prior to XL Release 2.1, an incorrect result could be returned from the 'ctime' function if the TZ variable and/or the hardware clock were set incorrectly. The 'time' function, which is used in combination with 'ctime', has been modified to eliminate the possibility of an incorrect result. OTHER NEW FEATURES The HP C Reference Manual and the HP C/XL Reference Manual Supplement are combined into a single new manual, the HP C/XL Reference Manual (P/N 31506-60001), which is thoroughly revised to reflect the new features of the language.