# std::longjmp

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< cpp‎ | utility‎ | program

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 `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)

No destructors for automatic objects are called. If replacing of `std::longjmp` with throw and setjmp with catch would execute a non-trivial destructor for any automatic object, the behavior of such `std::longjmp` is undefined.

### 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

`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

Run this code

    #include <iostream>
    #include <csetjmp>

    std::jmp_buf jump_buffer;

    [[noreturn]] void a(int count)
    {
        std::cout << "a(" << count << ") called\n";
        std::longjmp(jump_buffer, count+1);  // setjmp() will return count+1
    }

    int main()
    {
        volatile int count = 0; // local variables must be volatile for setjmp
        if (setjmp(jump_buffer) != 9) {
            a(count++);  // This will cause setjmp() to exit
        }
    }

Output:

    a(0) called
    a(1) called
    a(2) called
    a(3) called
    a(4) called
    a(5) called
    a(6) called
    a(7) called
    a(8) called

### See also

setjmp | saves the context (function macro)

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