Unable to open file using CreateFile function - c++

Question

Ok so I've been following this tutorial: http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=4422&lngWId=3
And so far I've gotten everything to work, up until I need the program to load in a .raw audio file.
Here's the relevant code:
LPSTR loadAudioBlock(const char* filename, DWORD* blockSize)
{
HANDLE hFile = INVALID_HANDLE_VALUE;
DWORD size = 0;
DWORD readBytes = 0;
void* block = NULL;
//open the file
if((hFile = CreateFile((LPCWSTR)filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL)) == INVALID_HANDLE_VALUE)
return NULL;
// get it's size, allocate memory, and then read it into memory
size = GetFileSize(hFile, NULL);
block = HeapAlloc(GetProcessHeap(), 0, size);
ReadFile(hFile, block, size, &readBytes, NULL);
CloseHandle(hFile);
*blockSize = size;
return (LPSTR)block;
}
And then my main function which calls it:
int _tmain(int argc, _TCHAR* argv[])
{
HWAVEOUT hWaveOut; //device handle
WAVEFORMATEX wfx; //struct for format info
MMRESULT result; // for waveOut return values
LPSTR block;
DWORD blockSize;
// first let's set up the wfx format struct
wfx.nSamplesPerSec = 44100; // rate of the sample
wfx.wBitsPerSample = 16; //sample size
wfx.nChannels = 2; // 2 channels = stereo
wfx.cbSize = 0; // no extra info
wfx.wFormatTag = WAVE_FORMAT_PCM; //PCM format
wfx.nBlockAlign = (wfx.wBitsPerSample >> 3) * wfx.nChannels;
wfx.nAvgBytesPerSec = wfx.nBlockAlign * wfx.nSamplesPerSec;
// then let's open the device
if(waveOutOpen(&hWaveOut, WAVE_MAPPER, &wfx, 0, 0, CALLBACK_NULL) != MMSYSERR_NOERROR)
{
fprintf(stderr, "unable to open Wave Mapper device.\n");
Sleep(1000);
ExitProcess(1);
}
// if no errors then close it
printf("The Wave Mapper device was opened successfully!\n");
//load and play file
if((block = loadAudioBlock("ding.raw", &blockSize)) == NULL)
{
fprintf(stderr, "Unable to load file\n");
Sleep(1000);
ExitProcess(1);
}
writeAudioBlock(hWaveOut, block, blockSize);
Sleep(1000);
waveOutClose(hWaveOut);
return 0;
}
Everytime I run the program I get the: "Unable to load file" output. I've got the "ding.raw" file in the same directory as my exe. I've also tried doing the full path as "C://path" and "C:/path" but then the compiler just gives me more errors about being unable to load a pdb file.
Any ideas? I'm using the Visual Studio 2012 Professional IDE and compiler.

Answer 1

Instead of using the standard char you should be using e.g. _TCHAR and LPCTSTR everywhere. This will make all string and string pointers you pass around be correct.
Look at the argv argument to _tmain and you will see that it uses _TCHAR instead of char. This is because Windows support both normal characters and Unicode characters depending on a couple of macros. See e.g. here for some more information.
So to solve what is likely your problem (since you don't get the actual error code, see my comment about GetLastError) you should change the function like this:
void *loadAudioBlock(LPCTSTR filename, DWORD* blockSize)
{
// ...
if((hFile = CreateFile(filename, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL)) == INVALID_HANDLE_VALUE)
return NULL;
// ...
}
And call it like this:
// ...
void *block;
if((block = loadAudioBlock(_T("C:\\path\\ding.raw"), &blockSize)) == NULL)
{
fprintf(stderr, "unable to open Wave Mapper device, error code %ld.\n", GetLastError());
Sleep(1000);
ExitProcess(1);
}
// ...
As you can see I also changed the return type, as the file is binary and won't have any readable text.

Answer 2

LPSTR loadAudioBlock(const char* filename, DWORD* blockSize)
{
if((hFile = CreateFile(CA2T(filename), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL)) == INVALID_HANDLE_VALUE)
return NULL;
}
See ATL conversion macros: http://msdn.microsoft.com/en-us/library/87zae4a3%28v=vs.80%29.aspx Just casting const char* LPCWSTR doesn't work.