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Exceptions are exceptional conditions that require special handling. They include errors that occur at run time, such as divide by zero, and the exhaustion of free store. Exception handling provides a standard way of dealing with errors, discovering both anticipated and unanticipated problems, and enables developers to recognize, track down, and fix bugs.
When an error occurs, the program raises an exception, meaning it creates an exception object and rolls back the stack to the first point it finds where you have code to handle the exception. The exception object usually contains information about what happened. This allows another part of the program to diagnose the cause of the exception.
To make your applications robust, your code needs to recognize exceptions when they occur and respond to them. If you don't specify a response, the application presents a message box describing the error. Your job, then, is to recognize places where errors might happen, and define responses, particularly in areas where errors could cause the loss of data or system resources.
When you create a response to an exception, you do so on blocks of code. When you have a series of statements that all require the same kind of response to errors, you can group them into a block and define error responses that apply to the whole block.
Blocks with specific responses to exceptions are called protected blocks because they can guard against errors that might otherwise either terminate the application or damage data.
See Defining Protected Blocks for details on how to create and handle exceptions.
For information on using exceptions with the routines and classes in VCL, see Handling Exceptions in VCL Applications.