The header <setjmp.h> defines the macro setjmp, and declares one function and one type, for bypassing the normal function call and return discipline.
The type declared is
jmp_buf
which is an array type suitable for holding the information needed to restore a calling environment.
#include <setjmp.h>
int
setjmp (jmp_buf
env );
The setjmp macro saves its calling environment in its jmp_buf argument for later use by the longjmp function.
If the return is from a direct invocation, the setjmp macro returns the value zero. If the return is from a call to longjmp function, the setjmp macro returns a nonzero value.
An invocation of the setjmp macro shall appear in one of the following contexts:
the entire controlling expression of a selection or iteration statement:
one operand of a relational or equality operator with the other operand an integral constant expression, with the resulting expression being the entire controlling expression of a selection or iteration statement:
the operand of a unary ! operator with the resulting expression being the entire controlling expression of a selection or iteration statement: or
the entire expression of an expression statement (possibly cast to void).
If the program is running with expanded memory, then the address state is also saved in the jmp_buf argument.