From cppreference.com
#define setjmp(env) /* implementation-defined */Saves the current execution context into a variable env of type
. This variable can later be used to restore the current execution context by
function. That is, when a call to
function is made, the execution continues at the particular call site that constructed the
variable passed to
. In that case setjmp returns the value passed to
.
The invocation of setjmp must appear only in one of the following contexts:
the entire controlling expression of
,
,
,
,
.switch(setjmp(env)){// ...
one operand of a relational or equality operator with the other operand an integer constant expression, with the resulting expression being the entire controlling expression of
,
,
,
,
.if(setjmp(env)>0){// ...
the operand of a unary ! operator with the resulting expression being the entire controlling expression of
,
,
,
,
.while(!setjmp(env)){// ...
the entire expression of an
(possibly cast to void).setjmp(env);
If setjmp appears in any other context, the behavior is undefined.
Additionally, the behavior is undefined if setjmp is invoked in a
in a place where the co_await operator may be used.
(since C++20)Upon return to the scope of setjmp:
all accessible objects, floating-point status flags, and other components of the abstract machine have the same values as they had when
was executed,
except for the non-
local variables in the function containing the invocation of setjmp, whose values are indeterminate if they have been changed since the setjmp invocation.
Parameters
env - variable to save the execution state of the program to Return value
0 if the macro was called by the original code and the execution context was saved to env.
Non-zero value if a non-local jump was just performed. The return value is the same as passed to
.
Notes
Above requirements forbid using return value of setjmp in data flow (e.g. to initialize or assign an object with it). The return value can only be either used in control flow or discarded.
Example
Run this code
#include<array>#include<cmath>#include<csetjmp>#include<cstdlib>#include<format>#include<iostream>std::jmp_bufsolver_error_handler;std::array<double,2>solve_quadratic_equation(doublea,doubleb,doublec){constdoublediscriminant=b*b-4.0*a*c;if(discriminant<0)std::longjmp(solver_error_handler,true);// Go to error handlerconstdoubledelta=std::sqrt(discriminant)/(2.0*a);constdoubleargmin=-b/(2.0*a);return{argmin-delta,argmin+delta};}voidshow_quadratic_equation_solution(doublea,doubleb,doublec){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);}intmain(){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 See also