# setjmp

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Defined in header `<csetjmp>` |  |
#define setjmp(env) /* implementation-defined */ |  |

Saves the current execution context into a variable env of type std::jmp_buf. This variable can later be used to restore the current execution context by std::longjmp function. That is, when a call to std::longjmp function is made, the execution continues at the particular call site that constructed the std::jmp_buf variable passed to std::longjmp. In that case `setjmp` returns the value passed to std::longjmp.

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

1. the entire controlling expression of `if`, `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 of `if`, `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 of `if`, `switch`, `while`, `do-while`, `for`.

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

4. the entire expression of an expression statement (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 coroutine 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 std::longjmp was executed,
- except for the non-volatile 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 std::longjmp.

### 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 <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
        }
    }

Output:

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

### See also

longjmp | jumps to specified location (function)

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