Saves the current execution context into a variableenv of typestd::jmp_buf. This variable can later be used to restore the current execution context bystd::longjmp function. That is, when a call tostd::longjmp function is made, the execution continues at the particular call site that constructed thestd::jmp_buf variable passed tostd::longjmp. In that casesetjmp returns the value passed tostd::longjmp.

The invocation ofsetjmp must appear only in one of the following contexts:

1. the entire controlling expression ofif,switch,while,do-while,for.

   switch(setjmp(env)){// ...

2. 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 ofif,switch,while,do-while,for.

   if(setjmp(env)>0){// ...

3. the operand of a unary ! operator with the resulting expression being the entire controlling expression ofif,switch,while,do-while,for.

   while(!setjmp(env)){// ...

4. the entire expression of anexpression statement (possibly cast tovoid).

   setjmp(env);

Ifsetjmp appears in any other context, the behavior is undefined.

Upon return to the scope ofsetjmp:

• all accessible objects, floating-point status flags, and other components of the abstract machine have the same values as they had whenstd::longjmp was executed,
• except for the non-volatile local variables in the function containing the invocation ofsetjmp, whose values are indeterminate if they have been changed since thesetjmp invocation.

[edit]Parameters

[edit]Return value

​0​ if the macro was called by the original code and the execution context was saved toenv.

Non-zero value if a non-local jump was just performed. The return value is the same as passed tostd::longjmp.

[edit]Notes

Above requirements forbid using return value ofsetjmp 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.

[edit]Example

#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;}

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

[edit]See also

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