Leaving Routine in ON ERROR in FoxBASE+ or FoxPro

• Microsoft Visual FoxPro for Windows, version 3.0
• Microsoft FoxBASE+ for MS-DOS, versions 1.21 and 2.1
• Microsoft FoxPro for MS-DOS, versions 1.0, 1.01, 1.02, 2.0, 2.5, and 2.5a
• Microsoft FoxPro for Windows, versions 2.5 and 2.5a

SUMMARY

You can use the following methods to leave the routine specified in an ON ERROR command:

• Use the RETURN TO MASTER command to return to the highest level program. For example, if the Run menu pad is present on the FoxPro system menu bar (FOXSTART.APP was executed on startup), the RETURN TO MASTER command returns control to FOXSTART.APP.
• Use the RETURN command to return to the program that had the error and continue execution on the next line. For example, the RETURN command terminates execution of a program or a user-defined function (UDF) and returns control to either the calling program, the highest level calling program, another program, or the Command window.

  Using a RETURN command at the end of a program or a user-defined function is optional because an implicit RETURN command automatically follows the last statement in a program file. Private memory variables are released when the RETURN command is executed.

• Use the RETRY command to return to the program that had the error and execute the line that had the error. For example, the RETRY command returns control to the calling program and reexecutes the last line that was executed in that program. The RETRY command is similar to the RETURN command except that the RETURN command causes the next line in the calling program to be executed rather than reexecuting the most recently executed line. RETRY is especially useful in error-handling routines or when a set of commands should be repeated until a certain condition is true.

  In FoxPro/LAN (the networked version of FoxPro), the RETRY command is frequently used to repeat a command until a record or file becomes available for use. The SET REPROCESS command can be used to control the number of times a command is repeated when it is unable to access a record or a file. In most network situations, the SET REPROCESS command is preferred.

MORE INFORMATION

The ON ERROR command traps errors that occur during program execution. When an error occurs, the trap is triggered and the specified command is executed. An ON ERROR routine may be deactivated by issuing another ON ERROR command that does not specify a command to run.

If the command specified in the ON ERROR command is DO <program>, specifying the ERROR(), LINENO(), MESSAGE(), and PROGRAM() functions as parameters passes the cause of the error, the line number where the error occurred, the error message, and the name of the program that had the error to the error handling function. This information can be valuable during the process of debugging an application.

After the ON ERROR routine completes, program execution resumes on the line immediately following the line that causes the error. However, if the specified command is DO <program> and the <program> ends with a RETRY command, execution resumes on the line on which the error occurred.

In FoxPro/LAN, an ON ERROR routine may be used to trap for errors created when a command that attempts to lock a record or a file is unsuccessful. If an ON ERROR routine is not in effect, FoxPro displays an error message that indicates why the record lock or file lock is unsuccessful (for example, "Record is in use by another"). If an ON ERROR routine is in effect, FoxPro does not display an error message and it executes the ON ERROR routine. Note that an unsuccessful lock attempt by the explicit locking functions [FLOCK(), LOCK(), and RLOCK()] does not trigger an ON ERROR routine or cause an error message to be displayed. Instead, these functions return a logical truth value (.F. or .T.) to indicate the failure or success of the lock attempt.

Sample Code

   ON ERROR DO errhand WITH ;
      ERROR(), MESSAGE(), MESSAGE(1), PROGRAM(), LINENO()

   *** The next line should cause an error. ***

   USE nodatabase

   PROCEDURE errhand
   PARAMETER merror, mess, mess1, mprog, mlineno
   ? 'Error number: ' + LTRIM(STR(merror))
   ? 'Error message: ' + mess
   ? 'Line of code with error: ' + mess1
   ? 'Line number of error: ' + LTRIM(STR(mlineno))
   ? 'Program with error: ' + mprog