How to std::mutex::lock until function returns

Question

I want to return a std::vector. This std::vector may be accessed from other threads (read and write). How can I unlock my std::mutex just after the function has finished returning?

For example in something like:

// Value.cpp
std::vector<int> GetValue()
{
  std::lock_guard<std::mutex> lock(mutex);

  // Do super smart stuff here
  // ...

  return m_value;
}

// MyThread.cpp
auto vec = myVec.GetValue();

Now what if "Do super smart stuff here" is empty:

// Value.cpp
std::vector<int> GetValue()
{
  std::lock_guard<std::mutex> lock(mutex);
  return m_value;
}

// MyThread.cpp
auto vec = myVec.GetValue();

Then is the lock still mandatory? Why?

Answer 1

Use a std::lock_guard to handle locking and unlocking the mutex via RAII, that is literally what it was made for.

int foo()
{
    std::lock_guard<std::mutex> lg(some_mutex);  // This now locked your mutex
    for (auto& element : some_vector)
    {
        // do vector stuff
    }
    return 5;
}  // lg falls out of scope, some_mutex gets unlocked

After foo returns, lg will fall out of scope, and unlock some_mutex when it does.