C - Windows Exception Handler Invalid Handle - c

Question

I have a problem about managing an exception. In my code I put hIn = INVALID_HANDLE_VALUE to test the exception, and "null" is a non existing file. My piece of code is
__try
{
hIn = CreateFile (_T("null"), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
hIn = INVALID_HANDLE_VALUE;
ReadFile (hIn, buffer, BUF_SIZE*sizeof(DWORD), &nIn, NULL);
}
__except(GetExceptionCode() == EXCEPTION_INVALID_HANDLE ? EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH)
{
_tprintf (_T("-> Error OPENING FILE <-\n"));
return -1;
}
I don't understand why it doesn't catch the exception. What is the problem?
Thank you in advance

Answer 1

The __except block is never entered because ReadFile does not throw exceptions.
Remember that the Windows API is agnostic of programming language and needs to present an interface that can be consumed by any programming language. And not all languages have support for exceptions, and even those that do use different mechanisms. So for an API like the Windows API, throwing exceptions is simply not an option.
Both of the API calls in your question indicate errors by their return values. You need to check these return values and act accordingly. Not all functions report errors in the same way so you need to pay close attention to the documentation for each API function that you call.

Answer 2

The C-function (Win32 API) ReadFile() doesn't normally throw an exception. Instead check return value of ReadFile and if FALSE, call GetLastError() to get the error code.
Have you btw enabled SEH ? See compiler switch /EHsc
see

Answer 3

As others have stated, your __except does not catch an exception because there is no exception being raised in the first place. You need to check return values and error codes instead:
hIn = CreateFile (_T("null"), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if (hIn == INVALID_HANDLE_VALUE)
{
_tprintf (_T("-> Error %u OPENING FILE <-\n"), GetLastError());
return -1;
}
...
ReadFile (hIn, buffer, BUF_SIZE*sizeof(DWORD), &nIn, NULL);
...
CloseHandle(hIn);