CODEWITHSUNDEEP
c++exceptiondirectx
mitchellJ
mitchellJ

Reputation: 734

DirectX Exception handling

I'm following the rastertek tutorial on DirectX while also studying Exception-Safety in Generic Components by David Abrahams (http://www.boost.org/community/exception_safety.html).

Why (to the best of anyone's knowledge) is the exception handling set up the way it is in the rastertek tutorial and what level of protection does it offer?

For instance:

mhresult = D3D11CreateDeviceAndSwapChain(NULL, D3D_DRIVER_TYPE_HARDWARE, NULL, 0, &mfeatureLevel, 1,
    D3D11_SDK_VERSION, &mswapChainDesc, &mswapChain, &mdevice, NULL, &mdeviceContext);

if (FAILED(mhresult))
{
    return false;
}

if an unhandled exception occurs in the call to CreateDevice won't the program crash before we check the result of mhresult?

Does it make a difference whether we're calling a method with an HResult return value or just a boolean?

result = mEstablishHW();
if (!result)
{
    return false;
}

Is there an alternative approach that would provide strong exception safety without a performance impact?

Upvotes: 0

Views: 3039

Answers (2)

Drop
Drop

Reputation: 13003

DirectX is a COM-based API. And exceptions are not allowed to cross COM boundary. So no DirectX function exists that ever throw. Instead, they use C-style return codes, which are called HRESULT, to indicate errors.

To effectively work with DirectX, obviously you should learn at least some basics of COM. But here are tips to start with, to make your initial code safer and to simplify debugging:

  • Always always always check return code. It doesn't mean you should write if/else each time. Write a macro that will check HRESULT, break a debugger in case of "not S_OK", and tell you a file, line and function where it happened. You could also convert HRESULT to readable string and output it (in console).
  • It is a good idea, to check output objects if they are valid (i.e. not "NULL"): mswapChain, mdevice, mdeviceContext in your example.
  • Use DirectX debug layer: D3D11_CREATE_DEVICE_DEBUG
  • Use Graphics diagnostics tools: one is built into Visual Studio since 2012, Nvidia Nsight is very good too
  • Finally, read the docs! MSDN isn't perfect, but DirectX docs are pretty well-written.

Anyway, DirectX is not the API to start to learn exception safety. Maybe Standard library (like trying to write proper swap function for your classes) or Boost (like filesystem) will work better for that purpose.

Upvotes: 7

Ross Ridge
Ross Ridge

Reputation: 39591

DirectX doesn't use exceptions to report errors or anything else. The DirectX interfaces are meant to be compiler agnostic and using C++ exceptions would tie their use to a specific compiler because of ABI differences. Even different versions Microsoft C++ would be incompatible because of ABI differences.

Since most DirectX methods and functions return an HRESULT value, you'll want to check for errors like in your first example. You can then throw an exception in your own code if that makes sense for your project.

Upvotes: 0

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