HP 3000 Manuals HP 3000 Manuals
ERROR HANDLING There are basically two types of errors that can occur as a result of calling VPLUS/V intrinsics. The first type consists of errors in the intrinsic call itself or in an attempt to access a file used by the called intrinsic. The second type are errors detected by editing data entered into FORMSPEC forms. These two error types are handled differently by VPLUS/V. Intrinsic Call or File Errors If a call to a VPLUS/V intrinsic causes an error so that the intrinsic cannot be executed correctly, or if an MPE file error occurs as a result of an attempt to access a file with a VPLUS/V intrinsic, the comarea word cstatus is set to a nonzero value. In addition, the number associated with an MPE file error is stored in the comarea word, filerrnum. When cstatus is not zero, any subsequent VPLUS/V intrinsics called by the application return to the application without executing. As part of good programming practice, check cstatus after each call, report the error, and then reset cstatus. There is one exception--VERRMSG uses cstatus to determine the error number. If cstatus is set to zero (indicating no error) prior to the call to VERRMSG, then no message is returned. Editing Errors Field processing may be specified in the forms description with FORMSPEC and checked by VFIELDEDITS, VINITFORM, or VFINISHFORM; or editing may be provided by user routines in an application. Each field in a FORMSPEC form has an error flag associated with it. When one of the VPLUS/V intrinsics that performs field processing (VFIELDEDITS, VINITFORM or VFINISHFORM) detects a field error, it sets the error flag for that field. It also increments numerrs, the word in comarea that contains the total number of fields with errors in each form. If a user-provided editing routine detects a field error, the program must call the VPLUS/V intrinsic VSETERROR in order to set the field error flag and increment numerrs. The cstatus item is not set when an editing error is detected and subsequent intrinsics may be executed without resetting this comarea item. If new data is written to a field in the data buffer that had an error, the error flag for the field is cleared and numerrs is decremented. VPUTBUFFER, VPUTFIELD, or VPUTtype are the intrinsics that can correct field errors and decrement numerrs. The intrinsic VREADFIELDS resets numerrs to zero when it reads new data into the buffer from the terminal. If numerrs has been set to a nonzero value by one of the VPLUS/V edit intrinsics, then VREADFIELDS with reset it to zero. Also, when VGETNEXTFORM is called, numerrs is reset to zero. Error Messages Messages associated with all VPLUS/V-detected errors can be retrieved by a call to VERRMSG. This intrinsic uses the error message file whose MPE file number is kept in the comarea word, errfilenum The error message file contains internal error numbers linked to particular field errors. Error messages may be general VPLUS/V messages (see Appendix B), or custom messages specified during forms design with FORMSPEC. In either case, the message is returned to the calling program by VERRMSG. VERRMSG determines the type of the error by examining cstatus and numerrs. If cstatus is not zero, its value indicates a particular intrinsic call error. If cstatus is zero and numerrs is set, VERRMSG knows the error is an editing error and uses internal values to locate the error in the error message file. If an editing error is detected by a user routine, the program must provide its own message when it calls VSETERROR to set the error flag for the field. Determining Fields in Error VGETFORMINFO provides a method of determining which fields are flagged in error by the editing routines. VFIELDEDITS sets an error flag for each field that failed edit checks. Only the error number of the first field in error and the number of errors have been returned to an application by VFIELDEDITS via the comarea. All fields in error are enhanced with the error enhancement if VSHOWFORM is called after VFIELDEDITS. To enable applications to determine which fields are in error for a given form at run-time, VGETFORMINFO optionally returns data about these error flags to show which fields failed the edit checks.