int setjmp (jmp_buf
void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__
While the C language has the dreaded goto statement, it can only be used to jump to a label in the same (local) function. In order to jump directly to another (non-local) function, the C library provides the setjmp() and longjmp() functions. setjmp() and longjmp() are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.
setjmp() and longjmp() make programs hard to understand and maintain. If possible, an alternative should be used.
longjmp() can destroy changes made to global register variables (see How to permanently bind a variable to a register?).
For a very detailed discussion of setjmp()/longjmp(), see Chapter 7 of Advanced Programming in the UNIX Environment, by W. Richard Stevens.
int main (void)
if (setjmp (env))
... handle error ...
... main processing loop which calls foo() some where ...
void foo (void)
... blah, blah, blah ...
longjmp (env, 1);
(jmp_buf __jmpb, int __ret)
Non-local jump to a saved stack context.
longjmp() restores the environment saved by the last call of setjmp() with the corresponding __jmpb argument. After longjmp() is completed, program execution continues as if the corresponding call of setjmp() had just returned the value __ret.
longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second argument of 0, 1 will be returned instead.
__jmpb Information saved
by a previous call to setjmp().
__ret Value to return to the caller of setjmp().
This function never returns.
Save stack context for non-local goto.
setjmp() saves the stack context/environment in __jmpb for later use by longjmp(). The stack context will be invalidated if the function which called setjmp() returns.
__jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored.
setjmp() returns 0 if returning directly, and non-zero when returning from longjmp() using the saved context.
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