Rexx - Error Handling


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Rexx has the ability to also work on Error handling as in other programming languages.

The following are some of the various error conditions that are seen in Rexx.

  • ERROR − This even is raised whenever a command which is sent to the operating system results in an error.

  • FAILURE − This even is raised whenever a command which is sent to the operating system results in a failure.

  • HALT − This is normally raised whenever an operation is dependent on another operation. An example is if an I/O operation is being halted for any reason.

  • NOVALUE − This event is raised when a value has not been assigned to a variable.

  • NOTREADY − This is raised by any I/O device which is not ready to accept any operation.

  • SYNTAX − This event is raised if there is any syntax error in the code.

  • LOSTDIGITS − This event is raised when an arithmetic operation results in a loss of digits during the operation.

Trapping Errors

Errors are trapped with the help of the signal command. Let’s take a look at the syntax and an example of this.

Syntax

signal on [Errorcondition]

Where,

  • Errorcondition − This is the error condition which is given above.

Example

Let’s take a look at an example on this.

/* Main program */ 
signal on error 
signal on failure 
signal on syntax 
signal on novalue beep(1) 
signal off error 
signal off failure
signal off syntax 
signal off novalue 
exit 0 
error: failure: syntax: novalue: 
say 'An error has occured'

In the above example, we first turn the error signals on. We then add a statement which will result in an error. We then have the error trap label to display a custom error message.

The output of the above program will be as shown below.

An error has occurred.

An example of error codes is shown in the following program.

/* Main program */ 
signal on error 
signal on failure 
signal on syntax 
signal on novalue beep(1) 
exit 0 
error: failure: syntax: novalue: 

say 'An error has occured' 
say rc 
say sigl 

The output of the above program will be as shown below.

An error has occured 
40 
6


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