### 23.3 Non-Local Exits and Signals

In BSD Unix systems, `setjmp` and `longjmp` also save and restore the set of blocked signals; see Blocking Signals. However, the POSIX.1 standard requires `setjmp` and `longjmp` not to change the set of blocked signals, and provides an additional pair of functions (`sigsetjmp` and `siglongjmp`) to get the BSD behavior.

The behavior of `setjmp` and `longjmp` in the GNU C Library is controlled by feature test macros; see Feature Test Macros. The default in the GNU C Library is the POSIX.1 behavior rather than the BSD behavior.

The facilities in this section are declared in the header file `setjmp.h`.

— Data Type: sigjmp_buf

> This is similar to `jmp_buf`, except that it can also store state information about the set of blocked signals.

— Function: int sigsetjmp (sigjmp_buf state, int savesigs)

> This is similar to `setjmp`. If savesigs is nonzero, the set of blocked signals is saved in state and will be restored if a `siglongjmp` is later performed with this state.

— Function: void siglongjmp (sigjmp_buf state, int value)

> This is similar to `longjmp` except for the type of its state argument. If the `sigsetjmp` call that set this state used a nonzero savesigs flag, `siglongjmp` also restores the set of blocked signals.