Termination-Handler Syntax - Win32 Programmer's Reference

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Termination-Handler Syntax

The try and finally keywords are used to construct a termination handler. The following example shows the structure of a try-finally termination handler.

try {

// guarded body of code

}

finally {

// finally block

}

As with the try-except statement, both the try block and the finally block require braces ({}), and using a goto statement to jump into either block is not permitted.

The try block contains the guarded body of code that is protected by the termination handler. A function can have any number of try-finally statements, and these termination handling structures can be nested within the same function or in different functions.

The finally block is executed whenever the flow of control leaves the try block. However, the finally block is not executed if either the ExitProcess or ExitThread function is called from within the try block.

If execution of the try block terminates because of an exception that invokes the exception-handling block of a frame-based exception handler, the finally block is executed before the exception-handling block is executed. Similarly, a call to the standard C longjmp function from the try block causes execution of the finally block before execution resumes at the target of the longjmp operation. If try block execution terminates due to a normal control statement (return, break, continue, or goto), the finally block is executed.

The AbnormalTermination function can be used within the finally block to determine whether the try block terminated sequentially

that is, whether it reached the closing brace (}). Leaving the try block because of a call to longjmp, a jump to an exception handler, or a return, break, continue, or goto statement, is considered an abnormal termination. Note that failure to terminate sequentially causes the system to search backward through all stack frames to determine whether any termination handlers must be called. This can result in performance degradation due to the execution of hundreds of instructions.

Execution of the finally block can terminate by any of the following means.

Execution of the last statement in the block and continuation to the next instruction
Use of a normal control statement (return, break, continue, or goto)
Use of longjmp or a jump to an exception handler

The finally block is executed in the context of the function in which the try-finally statement is located. This means that the finally block can access that function's local variables.

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