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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). 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 conditions where the function cannot return meaningfully. C++ generally uses excep- tion 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 han- dler 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 {}x + {}x + {} = 0...\n", a, b, c); auto [x_0, x_1] = solve_quadratic_equation(a, b, c); std::cout << std::format("x = {}, x = {}\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 1x + -3x + 2 = 0... x = 1, x = 2 Solving 2x + -3x + -2 = 0... x = -0.5, x = 2 Solving 1x + 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 Cor- rect behavior LWG 619 C++98 the wording of the extra restrictions improved the wording in C++ was vague the behavior was undefined if the behav- ior is only replacing undefined LWG 894 C++98 std::longjmp with throw and setjmp if a non- trivial destructor with for catch would destroy any automatic any auto- matic 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)
NAME | Synopsis | Parameters | Return value | Notes | Example | Output: | See also
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