m4_comment([$Id: cxx.so,v 1.3 2002/08/27 02:28:31 bostic Exp $])

m4_ref_title(Upgrading m4_db Applications,
    Release 4.1: C++ exceptions,,
    upgrade.4.1/java, upgrade.4.1/app_dispatch)

m4_p([dnl
With default flags, the C++ m4_refcxx(DbEnv) and m4_refcxx(Db) classes
can throw exceptions from their constructors.  For example, this can
happen if invalid parameters are passed in or the underlying C
structures could not be created.  If the objects are created in an
environment that is not configured for exceptions (that is, the
m4_ref(DB_CXX_NO_EXCEPTIONS) flag is specified), errors from the
constructor will be returned when the handle's open method is called.])

m4_p([dnl
In addition, the behavior of the m4_refcxx(DbEnv) and m4_refcxx(Db)
destructors has changed to simplify exception handling in applications.
The destructors will now close the handle if the handle's close method
was not called prior to the object being destroyed.  The return value
of the call is discarded, and no exceptions will be thrown.
Applications should call the close method in normal situations so any
errors while closing can be handled by the application.])

m4_p([dnl
This change allows applications to be structured as follows:])

m4_indent([dnl
try {
	DbEnv env(0);
	env.open(/* ... */);
	Db db(&env, 0);
	db.open(/* ... */);
	/* ... */
	db.close(0);
	env.close(0);
} catch (DbException &dbe) {
	// Handle the exception, the handles have already been closed.
}])

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