#include <setjmp.h>void _longjmp(jmp_buf env, int val);
If _longjmp() is called even though env was never initialized by a call to _setjmp(), or when the last such call was in a function that has since returned, the results are undefined.
No errors are defined.
If _longjmp() is executed and the environment in which _setjmp() was executed no longer exists, errors can occur. The conditions under which the environment of the _setjmp() no longer exists include exiting the function that contains the _setjmp() call, and exiting an inner block with temporary storage. This condition might not be detectable, in which case the _longjmp() occurs and, if the environment no longer exists, the contents of the temporary storage of an inner block are unpredictable. This condition might also cause unexpected process termination. If the function has returned, the results are undefined.
Passing longjmp() a pointer to a buffer not created by setjmp(), passing _longjmp() a pointer to a buffer not created by _setjmp(), passing siglongjmp(3C) a pointer to a buffer not created by sigsetjmp(3C) or passing any of these three functions a buffer that has been modified by the user can cause all the problems listed above, and more.