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std::longjmp(3)		      C++ Standard Libary	       std::longjmp(3)

NAME
       std::longjmp - std::longjmp

Synopsis
	  Defined in header <csetjmp>
	  void	longjmp(  std::jmp_buf env, int	status );		(until
       C++17)
	  [[noreturn]] void longjmp( std::jmp_buf env, int status  );	(since
       C++17)

	  Loads	 the execution context env saved by a previous call to setjmp.
       This function
	  does not return. Control is transferred to  the  call	 site  of  the
       macro setjmp that
	  set  up  env.	That setjmp then returns the value, passed as the sta-
       tus.

	  If the function that called setjmp has exited, the behavior is unde-
       fined (in other
	  words, only long jumps up the	call stack are allowed)

	  No destructors for automatic objects are  called.  If	 replacing  of
       std::longjmp with
	  throw	 and  setjmp with catch	would execute a	non-trivial destructor
       for any automatic
	  object, the behavior of such std::longjmp is undefined.

Parameters
	  env	 - variable referring to the execution state  of  the  program
       saved by	setjmp
	  status  - the	value to return	from setjmp. If	it is equal to 0, 1 is
       used
		   instead

Return value
	  (none)

Notes
	  longjmp is the mechanism used	in C to	handle unexpected error	condi-
       tions where the
	  function cannot return meaningfully. C++  generally  uses  exception
       handling	for this
	  purpose.

Example
       // Run this code

	#include <iostream>
	#include <csetjmp>

	std::jmp_buf my_jump_buffer;

	[[noreturn]] void foo(int count)
	{
	    std::cout << "foo("	<< count << ") called\n";
	    std::longjmp(my_jump_buffer,  count+1);   //  setjmp() will	return
       count+1
	}

	int main()
	{
	    volatile int count = 0; // modified	locals in setjmp scope must be
       volatile
	    if (setjmp(my_jump_buffer) != 5) { //  equality  against  constant
       expression in an	if
		count	=   count  +  1;  //  ++count,	count  +=  1,  etc  on
       'volatile'-qualified
				   // left operand are deprecated since	 C++20
       (P1152)
		foo(count); // This will cause setjmp()	to exit
	    }
	}

Output:
	foo(1) called
	foo(2) called
	foo(3) called
	foo(4) called

See also
	  setjmp saves the context
		 (function macro)

http://cppreference.com		  2022.07.31		       std::longjmp(3)

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