Delphi in a Nutshell

Name

ExceptClsProc Variable

Syntax

var ExceptClsProc: Pointer;

function ExceptClassProc(var Rec: TExceptionRecord): TClass;
begin
  ...
end;
ExceptClsProc := @ExceptClassProc;

Description

Delphi calls the function that ExceptClsProc points to when a Windows exception occurs inside a try-except block that contains exception handlers (that is, where Delphi must test which exception handler matches the exception raised).

The sole argument to the ExceptClsProc function is a pointer to an exception record.

The class that ExceptClsProc returns must be the same type as the object that ExceptObjProc returns. Delphi uses the class from ExceptClsProc to identify which exception handler to use before it calls ExceptObjProc to create the exception object.

Tips and Tricks

• The Windows unit defines the TExceptionRecord type.

• The SysUtils unit sets ExceptClsProc to a function that maps all the Windows exceptions to appropriate Delphi exceptions, e.g., Status_Integer_Overflow becomes EIntOverflow.

Example

// Simple example of mapping Windows exceptions to custom exceptions. class CustomException = class(Exception); class CustomMathException = class(CustomException); class CustomRangeException = class(CustomException); function CustomExceptClsFunc(var Ex: TExceptionRecord): TClass; begin case Ex.ExceptionCode of STATUS_ARRAY_BOUNDS_EXCEEDED, STATUS_INTEGER_OVERFLOW: Result := CustomRangeException; STATUS_INTEGER_DIVIDE_BY_ZERO, STATUS_FLOAT_INEXACT_RESULT, STATUS_FLOAT_INVALID_OPERATION, STATUS_FLOAT_STACK_CHECK, ...