Exception handling

Exception handling in Delphi
An example of errors and handling them.

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Exception handling in Delphi

Below is some examples of how to implement error handling in Delphi. It's similar to Java (or Java is similiar to Delphi ) with it's try catch blocks. Detailed info on the Exception object is in the Delphi help file, along with a list of standard VCL E* exception objects.

{ ----- Simple Try/Except block ----- }
try
	// try something here
except
	// Exception, throw an error message
end;

{ ----- Try/Except/Finally block ----- }
try
	// Try something
except
	// Exception, throw an error message
finally
	// Do clean up code
end;

{ ----- Catching specific errors (prefered method) ----- }
try
	// Try something
except
	on EInvalidArgument do
	begin
		// Handle an EInvalidArgument exception here
	end;
	on EInvalidPointer do
	begin
		// Handle an EInvalidPointer exception here etc.
	end;
finally
	// Optional final clause
end;

{ ----- Raising an exception ----- }
// You can raise any object instance for an error.
if not i=1 then
begin
	raise EInvalidArgument.Create('Tut tut bad parameters used');
end;

{ ----- Creating your own exception ----- }
// This will derive the class from the Exception object
// which is the best way to do it. This means if you error
// object doesn't handle the error, the Exception object will.

// The exception object has the following methods:
// - Create - takes a string message as its parameter
// - CreateFmt - Variation on the create constructor, different args
// - CreateFmtHelp - Same as above
// - CreateHelp  - All the ones below + this one are the same
// - CreateRes 
// - CreateResFmt
// - CreateResFmtHelp
// - CreateResHelp
type
  EMyException = class(Exception);