Standard C++ Library Reference ISO/IEC (VERSION3)

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<setjmp.h>
Include the standard header <setjmp.h> to perform control transfers that bypass the normal
function call and return protocol.
#define setjmp(jmp_buf env) <int rvalue>
typedef a-type jmp_buf;
void longjmp(jmp_buf env, int val);
jmp_buf
typedef a-type jmp_buf;
The type is the array type a-type of an object that you declare to hold the context information
stored by setjmp and accessed by longjmp.
longjmp
void longjmp(jmp_buf env, int val);
The function causes a second return from the execution of setjmp that stored the current
context value in env. If val is nonzero, the return value is val; otherwise, it is 1.
The function that was active when setjmp stored the current context value must not have
returned control to its caller. An object with dynamic duration that does not have a volatile type
and whose stored value has changed since the current context value was stored will have a
stored value that is indeterminate.
setjmp
#define setjmp(jmp_buf env) <int rvalue>
The macro stores the current context value in the array designated by env and returns zero. A
later call to longjmp that accesses the same context value causes setjmp to again return, this
time with a nonzero value. You can use the macro setjmp only in an expression that:
has no operators●
has only the unary operator !●
has one of the relational or equality operators (==, !=, <, <=, >, or >=) with the other●