RPG - MONITOR - RPG School

MONITOR is a way to perform any set of instructions and then catch any eventual errors.
Useful when you know there is a risk of an error and you don’t want to blow up the program in the users face.

It’s a way of performing a “try-catch” sequence. Try something and if it didn’t work, catch the error and do something else.

It consists of 3 main elements:

monitor – States the beginning of the monitor group.
on-error – States that you catch any errors and allows you to write code to be run in the event of an error.
endmon – States the end of the monitor scope.

Example:

dcl-s counter int(5) inz;

counter = *hival;

monitor;
    // You can add as many lines of code you want here...
    counter += 3; // Try this
on-error;
    counter = 1234; // If an error occurred, just set the value to 1234
endmon;

dcl-s counter int(5) inz;

counter = *hival;

monitor;

// You can add as many lines of code you want here...

counter += 3; // Try this

on-error;

counter = 1234; // If an error occurred, just set the value to 1234

endmon;