|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 contextenv saved by a previous call tosetjmp. This function does not return. Control is transferred to the call site of the macrosetjmp that set upenv. Thatsetjmp then returns the value, passed as thestatus.
If the function that calledsetjmp has exited, the behavior is undefined (in other words, only long jumps up the call stack are allowed).
Contents |
On top of Clongjmp, C++std::longjmp has more restricted behavior.
If replacingstd::longjmp withthrow andsetjmp withcatch would invoke anon-trivial destructor for any automatic object, the behavior of suchstd::longjmp is undefined.
The behavior is undefined if | (since C++20) |
| env | - | variable referring to the execution state of the program saved bysetjmp |
| status | - | the value to return fromsetjmp. If it is equal to0,1 is used instead |
(none)
std::longjmp is the mechanism used in C to handle unexpected error conditions where the function cannot return meaningfully. C++ generally usesexception handling for this purpose.
#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){constdouble discriminant= b* b-4.0* a* c;if(discriminant<0) std::longjmp(solver_error_handler,true);// Go to error handler constdouble delta=std::sqrt(discriminant)/(2.0* a);constdouble 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 {}x² + {}x + {} = 0...\n", a, b, c);auto[x_0, x_1]= solve_quadratic_equation(a, b, c);std::cout<<std::format("x₁ = {}, x₂ = {}\n\n", x_0, x_1);} int main(){if(setjmp(solver_error_handler)){// Error handler for solverstd::cout<<"No real solution\n";returnEXIT_FAILURE;} for(auto[a, b, c]:{std::array{1,-3,2},{2,-3,-2},{1,2,3}}) show_quadratic_equation_solution(a, b, c); returnEXIT_SUCCESS;}
Output:
Solving 1x² + -3x + 2 = 0...x₁ = 1, x₂ = 2 Solving 2x² + -3x + -2 = 0...x₁ = -0.5, x₂ = 2 Solving 1x² + 2x + 3 = 0...No real solution
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 619 | C++98 | the wording of the extra restrictions in C++ was vague | improved the wording |
| LWG 894 | C++98 | the behavior was undefined if replacingstd::longjmp withthrow andsetjmp withcatch would destroy any automatic object | the behavior is only undefined if a non-trivial destructor for any automatic object is invoked |
| saves the context (function macro)[edit] | |
C documentation forlongjmp | |
