Runtime Error (Exception) Handling

ADA handles programmer defined exceptions and system defined exceptions

Some of the system defined exceptions are like 

1. NUMERIC_ERROR – raised whenever the abnormal precision in the program like divide by zero 
2. STORAGE-ERROR – raised whenever the program runs out of memory space
3. CONSTRAINT_ERROR – asserts when a variable goes out of its bound
4. TASKING_ERROR – raised during the incorrect use of tasks
5. PROGRAM_ERROR- raised whenever an exception is not captured by any other conditions

Example on Exceptions

//Program to create two programmer defined exceptions

declare 

P,PRESSURE:float;

HIGH_PRESSURE, LOW_PRESSURE:exception;

begin 

 loop

    P:=READ_PRESSURE(PRESSURE);

    if P

raise LOW_PRESSURE;

    elseif P>150 then 

raise HIGH_PRESSURE;

end if;

end loop;

exception 

when LOW_PRESSURE => put(“Warning: Very Low Pressure”);

when HIGH_PRESSURE => put (“Warning: High Pressure”);

• When exceptions are raised in multiple procedures or block and Procedures, handling the exceptions can be done using any of the procedure 
• For Example, If there are three procedures X,Y and Z. X calls Y and Y calls Z, now there is an exception at Z (which does not have exception handler), the control will transfer the previous procedure Y (Which contains the exception handling mechanism) and handled over there.
• Similary if a block does not have an exception handler, then the procedure which includes the block handles the expection , if that procedure contains the exception handler