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Warning C26811

Lifetime of the memory referenced by parameter 'var' might end by the time the coroutine is resumed.

Remarks

Warning C26811 is triggered when a variable might be used after its lifetime ended in a resumed coroutine.

Code analysis name: COROUTINES_USE_AFTER_FREE_PARAM

Example

The following code generates C26811.

#include <experimental/generator>
#include <future>

using namespace std::experimental;

// Simple awaiter to allows to resume a suspended coroutine
struct ManualControl
{
  coroutine_handle<>& save_here;

  bool await_ready() { return false; }
  void await_suspend(coroutine_handle<> h) { save_here = h; }
  void await_resume() {}
};

coroutine_handle<> g_suspended_coro;

std::future<void> async_coro(int &a)
{
  co_await ManualControl{g_suspended_coro};   // @expected(26811), Lifetime of 'a' might end by the time this coroutine is resumed.
  ++a;
}

To fix this warning, consider taking the argument by value:

std::future<void> async_coro(int a)
{
  co_await ManualControl{g_suspended_coro};
  ++a;
}

Alternatively, when the lifetime of a is guaranteed to outlive the lifetime of the coroutine, suppress the warning using gsl::suppress and document the lifetime contracts of the code.

See also

C26810