Google Benchmark, how to call code only once?

Question

I have a code snippet I need to benchmark composed of 2 parts, first the state needs to be set exactly once, next I need to actually benchmark a function.

My code looks like this:

static void BM_LoopTime(benchmark::State& state) 
{
    MasterEngine engine;
    for (auto _ : state)
    {
        engine.LoopOnce();
    }
}
BENCHMARK(BM_LoopTime);

In my output I am getting:

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Pointer already set                                                             
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Multiple times, which is a custom error message that indicates a very important pointer that should only ever be touched once is trying to be overwritten.

Calling that code multiple times is undefined behaviour in my implementation. How can I call the object initialization exactly once and then tell it to call the loop?

Answer 1

This is a work around that I found that's good enough for my use case but I am still looking for better solutions:

class MyFixture : public benchmark::Fixture 
{
public:
    std::unique_ptr<MasterEngine> engine;

    void SetUp(const ::benchmark::State& state) 
    {
        if(engine.get() == nullptr)
            engine = std::make_unique<MasterEngine>();
    }

    void TearDown(const ::benchmark::State& state) 
    {
    }
};