std::longjmp

             void longjmp( std::jmp_buf env, int status );

[[noreturn]] void longjmp( std::jmp_buf env, int status );

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).

Extra restrictions in C++

On top of C longjmp, C++ std::longjmp has more restricted behavior.

If replacing std::longjmp with throw and setjmp with catch would invoke a non-trivial destructor for any automatic object, the behavior of such std::longjmp is undefined.

Parameters

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 exception handling for this purpose.

Example

#include <csetjmp>
#include <iostream>
 
std::jmp_buf my_jump_buffer;
 
[[noreturn]] void foo(int status) 
{
    std::cout << "foo(" << status << ") called\n";
    std::longjmp(my_jump_buffer, status + 1); // setjmp() will return status + 1
}
 
int main()
{
    volatile int count = 0; // modified locals in setjmp scope must be volatile
    if (setjmp(my_jump_buffer) != 5) // equality against constant expression in an if
    {
        count += 1; // Increment of a volatile variable is deprecated since C++20 (P1152)
        foo(count); // This will cause setjmp() to exit
    }
}

foo(1) called
foo(2) called
foo(3) called
foo(4) called

Defect reports

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

See also