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11.5 Exception classes

The sysutils unit contains a great deal of exception handling. It defines the following exception types: 

        Exception = class(TObject)
         private
           fmessage : string;
           fhelpcontext : longint;
         public
           constructor create(const msg : string);
           constructor createres(indent : longint);
           property helpcontext : longint read fhelpcontext write fhelpcontext;
           property message : string read fmessage write fmessage;
        end;
        ExceptClass = Class of Exception;
        { mathematical exceptions }
        EIntError = class(Exception);
        EDivByZero = class(EIntError);
        ERangeError = class(EIntError);
        EIntOverflow = class(EIntError);
        EMathError = class(Exception);
The sysutils unit also installs an exception handler. If an exception is unhandled by any exception handling block, this handler is called by the Run-Time library. Basically, it prints the exception address, and it prints the message of the Exception object, and exits with a exit code of 217. If the exception object is not a descendent object of the Exception object, then the class name is printed instead of the exception message.

It is recommended to use the Exception object or a descendant class for all raise statements, since then the message field of the exception object can be used.

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