HP 3000 Manuals HP 3000 Manuals
HP C/XL Enhancements Erryl Johnson Systems Technology Division The 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. Two new libraries have been added for ANSI conformance. In addition, a change was made to the "time" function that assures the correct time will always be returned by "ctime". ANSI MODE The -Aa option enables ANSI mode when compiling a C program. The -Aa option may be used with the CCXL, CCXLLK and CCXLGO commands, or when running the C/XL compiler program CCOMXL.PUB.SYS directly. For example, to compile and link a program using ANSI mode, use CCXLLK MYTEXT,MYPROG;INFO="-Aa". If ANSI mode is not desired, use the -Ac option. If neither option is present ANSI mode will be disabled. ANSI LIBRARIES Two new libraries have been added for ANSI conformance. They are LIBCANSI.LIB.SYS and LIBMANSI.LIB.SYS. LIBCANSI contains a relocatable library that should be linked along with LIBCINIT or LIBC if conformance to ANSI is desired. It contains a flag that specifies that certain functions, primarily those that perform input/ output operations on text files, interrogate this flag and behave accordingly. If you use the CCXLLK or CCXLGO commands, then LIBCANSI.LIB.SYS will automatically be added to the RL list in the link step if you compiled in ANSI mode. LIBMANSI contains an ANSI-conforming version of the existing mathematical library, LIBM. The primary difference between the two libraries is in the way they handle an error, such as attempting to compute the square root of a negative value. The ANSI version of the library will call a user-written function named _matherr if one is provided, and no error message will be displayed. The older version of the library will call a user written function named matherr if one is provided. Otherwise, an error message will be displayed. CHANGE TO TIME FUNCTION Prior to XL Release 2.1, an incorrect result could be returned from the ctime function if either the TZ variable or the hardware clock or both were set incorrectly. The time function, which is used in combination with ctime, has been modified to eliminate the possibility of an incorrect result. How the TZ Variable is Applied In this release ctime works the same, but the time function no longer accesses the hardware clock. Instead, the time function uses the CALENDAR and CLOCK intrinsics to access the system timer, then adjusts that time according to the user's TZ variable to derive Greenwich Mean Time (GMT). When the value returned by the time function is passed to ctime, the TZ variable is applied again, in the opposite direction. This assures that the string returned by ctime will agree with the MPE XL system time, which is the time used by practically all other subsystems on MPE XL. Now, none of the C time functions access the hardware clock, so errors in setting that clock will not affect the C programmer. Likewise, if the TZ variable is not set, or is set incorrectly, the return from ctime will always be correct and agree with the MPE XL system time. Using the Time Function If you use the time function independently of the ctime function, to only obtain GMT, the TZ variable must now be set. Otherwise, the result from the time function may be incorrect. If the TZ variable is not set, or is invalid, the default is Eastern Time.