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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 status.

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

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
	std::longjmp  is the mechanism used in C to handle unexpected error con-
     ditions where
	the function cannot return meaningfully. C++  generally  uses  exception
     handling for
	this purpose.

Example
     // Run this code

      #include <array>
      #include <cmath>
      #include <csetjmp>
      #include <cstdlib>
      #include <format>
      #include <iostream>

      std::jmp_buf solver_error_handler;

      std::array<double,  2> solve_quadratic_equation(double a, double b, double
     c)
      {
	  const double discriminant = b * b - 4.0 * a * c;
	  if (discriminant < 0)
	      std::longjmp(solver_error_handler, true); // Go to error handler

	  const double delta = std::sqrt(discriminant) / (2.0 * a);
	  const double argmin = -b / (2.0 * a);
	  return {argmin - delta, argmin + delta};
      }

      void show_quadratic_equation_solution(double a, double b, double c)
      {
	  std::cout << std::format("Solving {}xA^2 + {}x + {} = 0...\n",  a,  b,
     c);
	  auto [x_0, x_1] = solve_quadratic_equation(a, b, c);
	  std::cout << std::format("xa = {}, xa = {}\n\n", x_0, x_1);
      }

      int main()
      {
	  if (setjmp(solver_error_handler))
	  {
	      // Error handler for solver
	      std::cout << "No real solution\n";
	      return EXIT_FAILURE;
	  }

	  for (auto [a, b, c] : {std::array{1, -3, 2}, {2, -3, -2}, {1, 2, 3}})
	      show_quadratic_equation_solution(a, b, c);

	  return EXIT_SUCCESS;
      }

Output:
      Solving 1xA^2 + -3x + 2 = 0...
      xa = 1, xa = 2

      Solving 2xA^2 + -3x + -2 = 0...
      xa = -0.5, xa = 2

      Solving 1xA^2 + 2x + 3 = 0...
      No real solution

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	  DR	Applied to	   Behavior  as  published		 Correct
     behavior
	LWG  619  C++98       the wording of the extra restrictions improved the
     wording
			   in C++ was vague
			   the behavior was undefined if	 the behavior is
     only
			   replacing				 undefined
	LWG 894 C++98	   std::longjmp with throw and setjmp	 if a  non-triv-
     ial destructor
			   with 				 for
			   catch  would  destroy any automatic	   any automatic
     object is
			   object				 invoked

See also
	setjmp saves the context
	       (function macro)
	C documentation for
	longjmp

http://cppreference.com 	   2024.06.10			 std::longjmp(3)
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