try-finally statement (C)
try-finally statement is a Microsoft extension to the C language that enables applications to guarantee execution of cleanup code when execution of a block of code is interrupted. Cleanup consists of such tasks as deallocating memory, closing files, and releasing file handles. The
try-finally statement is especially useful for routines that have several places where a check is made for an error that could cause premature return from the routine.
The compound statement after the
__try clause is the guarded section. The compound statement after the
__finally clause is the termination handler. The handler specifies a set of actions that execute when the guarded section is exited. It doesn't matter whether the guarded section is exited by an exception (abnormal termination) or by standard fall through (normal termination).
Control reaches a
__try statement by simple sequential execution (fall through). When control enters the
__try statement, its associated handler becomes active. Execution proceeds as follows:
The guarded section is executed.
The termination handler is invoked.
When the termination handler completes, execution continues after the
__finallystatement. No matter how the guarded section ends (for example, via a
gotostatement out of the guarded body or via a
returnstatement), the termination handler is executed before the flow of control moves out of the guarded section.
__leave keyword is valid within a
try-finally statement block. The effect of
__leave is to jump to the end of the
try-finally block. The termination handler is immediately executed. Although a
goto statement can be used to accomplish the same result, a
goto statement causes stack unwinding. The
__leave statement is more efficient because it doesn't involve stack unwinding.
try-finally statement using a
return statement or the
longjmp run-time function is considered abnormal termination. It's not legal to jump into a
__try statement, but legal to jump out of one. All
__finally statements that are active between the point of departure and the destination must be run. It's called a local unwind.
The termination handler isn't called if a process is killed while executing a
Structured exception handling works with C and C++ source files. However, it isn't specifically designed for C++. For portable C++ programs, C++ exception handling should be used instead of structured exception handling. Also, the C++ exception handling mechanism is much more flexible, in that it can handle exceptions of any type. For more information, see Exception handling in the C++ Language Reference.
See the example for the
try-except statement to see how the
try-finally statement works.