open_file_for_read_alow_delete.hpp

#include <io.h>
#include <fcntl.h>
#include <Windows.h>

auto open_file_for_read_alow_delete(const wchar_t filename[]) {
	struct result {
		FILE* fp;
		long long size;
		int error;
	};

	auto h = ::CreateFileW(filename,
		GENERIC_READ,
		FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
		nullptr, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, nullptr);
	if (h == INVALID_HANDLE_VALUE) {
		auto win32_error = ::GetLastError();
		return result{ nullptr, 0, HRESULT_FROM_WIN32(win32_error) };
	}

	LARGE_INTEGER size = {};
	if (!::GetFileSizeEx(h, &size)) {
		auto win32_error = ::GetLastError();
		::CloseHandle(h);
		return result{ nullptr, size.QuadPart, HRESULT_FROM_WIN32(win32_error) };
	}

	auto fd = _open_osfhandle(
		reinterpret_cast<intptr_t>(h), _O_RDONLY | _O_BINARY | _O_SEQUENTIAL);
	if (fd == -1) {
		const auto e = errno;
		::CloseHandle(h);
		return result{ nullptr, size.QuadPart, e };
	}

	auto fp = _fdopen(fd, "rb");
	if (!fp) {
		const auto e = errno;
		_close(fd);
		return result{ nullptr, size.QuadPart, e };
	}

	return result{ fp, size.QuadPart, 0 };
}