Exceptions

Table4.adb: Exception handler, overflow, constraint error and data error exceptions

• Table4.adb ( prettified )
• This version handles invalid input and also overflow during the calculations


• This version also uses a procedure to factor out common behavior from table3c.adb ( prettified )


• Exceptions handled by this routine
• Invalid Integer causes Data_Error


• Overflow causes Constraint_Error
• Must be compiled with -gnato to catch overflow


• skip_line skips all input through end of line (needed for interactive operation to skip newline)


• Define before use: declaration must precede call

Exception blocks

• Format:

       begin 
          ... 
       exception 
          when ... => 
             ... 
          when ... => 
             ... 
       end; 
       

• Flow of control:
• when a statement causes an exception, execution flows to the corresponding named when clause, if one exists, and then to the corresponding end.
• If no corresponding when clause exists, the program terminates.


• when others handles any other exceptions (How is this done in Java?)


• Begin-end block can be put anywhere


• Any begin end block can have an exception handler


• Note: any exception can be ignored (Is this true in Java?)

Raising Exceptions and User Defined Exceptions

• This program demonstrates the following:
  • User defined exceptions
  • Raising exceptions
  • Package Ada.Exceptions
  • Exception Names
  • Multiple names on one clause
  • Exceptions in a procedure begin-end block


• Example program: exceptions3.adb ( prettified )