HP 3000 Manuals HP 3000 Manuals
MPE XL Trap Handling Intrinsics In MPE XL, all access to user-defined trap handling routines is controlled by system intrinsics. The MPE XL trap handling intrinsics deal with the following types of trap situations: * Arithmetic trap * Software Library trap * Software System trap * CONTROL-Y trap Trap intrinsics can be invoked from within trap handling procedures. Arithmetic Traps An arithmetic trap handler reacts to arithmetic errors that occur as a result of arithmetic operations. The ARITRAP intrinsic enables or disables arithmetic traps. The XARITRAP intrinsic arms or disarms the user-written arithmetic trap handler. The HPENBLTRAP is similar in function to ARITRAP, but allows you greater flexibility in selectively enabling or disabling arithmetic traps. Software Library Traps A software library trap handler reacts to errors that occur during execution of procedures from the compiler libraries. You can arm or disarm your software library trap handler with the XLIBTRAP intrinsic. Software System Traps A software system trap handler reacts to certain errors that occur when user programs call intrinsics incorrectly. You arm or disarm your software system trap handler by means of the XSYSTRAP intrinsic. CONTROL-Y Traps If you are running a program in an interactive session, you can invoke a special trap that transfers control in the program to an armed, user-defined trap handling procedure when you enter a CONTROL-Y subsystem break signal from the terminal. On most terminals, this signal is transmitted by pressing the [[Y]] key while holding down the [[CTRL]] key. The XCONTRAP intrinsic arms or disarms the user-written CONTROL-Y trap handling procedure. If you send another CONTROL-Y signal, MPE XL ignores it unless you call the RESETCONTROL intrinsic at some point prior to the signal. Code-related Traps Code-related traps are handled solely by the MPE XL trap subsystem (that is, users cannot define their own routines to handle these traps). Code-related traps can occur as a result of illegal or incorrect coding practices.