Question

I’ve found some code on here that lists all the USB devices on a computer. Here’s the code:

#include <windows.h>
#include <devguid.h>    // for GUID_DEVCLASS_CDROM etc
#include <setupapi.h>
#include <cfgmgr32.h>   // for MAX_DEVICE_ID_LEN, CM_Get_Parent and CM_Get_Device_ID
#define INITGUID
#include "c:\WinDDK\7600.16385.1\inc\api\devpkey.h"
#include <tchar.h>
#include <stdio.h>
#include <iostream>

#define ARRAY_SIZE(arr)     (sizeof(arr)/sizeof(arr[0]))

#pragma comment (lib, "setupapi.lib")

typedef BOOL (WINAPI *FN_SetupDiGetDeviceProperty)(
  __in       HDEVINFO DeviceInfoSet,
  __in       PSP_DEVINFO_DATA DeviceInfoData,
  __in       const DEVPROPKEY *PropertyKey,
  __out      DEVPROPTYPE *PropertyType,
  __out_opt  PBYTE PropertyBuffer,
  __in       DWORD PropertyBufferSize,
  __out_opt  PDWORD RequiredSize,
  __in       DWORD Flags
);

// List all USB devices with some additional information
void ListUsbDevices(void)
{
    unsigned i, j;
    DWORD dwSize, dwPropertyRegDataType;
    DEVPROPTYPE ulPropertyType;
    OSVERSIONINFO osvi;
    CONFIGRET r;
    HDEVINFO hDevInfo;
    SP_DEVINFO_DATA DeviceInfoData;
    const static LPCTSTR arPrefix[3] = {TEXT("VID_"), TEXT("PID_"), TEXT("MI_")};
    TCHAR szDeviceInstanceID [MAX_DEVICE_ID_LEN];
    TCHAR szDesc[1024];
    LPTSTR pszToken, pszNextToken;
    TCHAR szVid[MAX_DEVICE_ID_LEN], szPid[MAX_DEVICE_ID_LEN], szMi[MAX_DEVICE_ID_LEN];

#ifdef UNICODE
    FN_SetupDiGetDeviceProperty fn_SetupDiGetDeviceProperty = (FN_SetupDiGetDeviceProperty)
        GetProcAddress (GetModuleHandle (TEXT("Setupapi.dll")), "SetupDiGetDevicePropertyW");
#else
    FN_SetupDiGetDeviceProperty fn_SetupDiGetDeviceProperty = (FN_SetupDiGetDeviceProperty)
        GetProcAddress(GetModuleHandle(TEXT("Setupapi.dll")), "SetupDiGetDevicePropertyA");
#endif

    // List all connected USB devices
    hDevInfo = SetupDiGetClassDevs (NULL, TEXT("USB"), NULL, DIGCF_PRESENT|DIGCF_ALLCLASSES);
    if (hDevInfo == INVALID_HANDLE_VALUE)
        return;

    // Find the ones that are driverless
    for (i = 0; ; i++)  {
        DeviceInfoData.cbSize = sizeof (DeviceInfoData);
        if (!SetupDiEnumDeviceInfo(hDevInfo, i, &DeviceInfoData))
            break;

        r = CM_Get_Device_ID(DeviceInfoData.DevInst, szDeviceInstanceID , MAX_PATH, 0);
        if (r != CR_SUCCESS)
            continue;

        _tprintf (TEXT("%s\n"), szDeviceInstanceID );

        if (SetupDiGetDeviceRegistryProperty (hDevInfo, &DeviceInfoData, SPDRP_DEVICEDESC,
                                              &dwPropertyRegDataType, (BYTE*)szDesc,
                                              sizeof(szDesc),   // The size, in bytes
                                              &dwSize))
            _tprintf (TEXT("    Device Description: \"%s\"\n"), szDesc);

        // Retreive the device description as reported by the device itself
        memset(&osvi, 0, sizeof(OSVERSIONINFO));
        osvi.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
        if ( (GetVersionEx(&osvi) != 0)
            && (osvi.dwBuildNumber >= 7000) ) {
                // On Vista and earlier, we can use only SPDRP_DEVICEDESC
                // On Windows 7, the information we want ("Bus reported device description") is
                // accessed through DEVPKEY_Device_BusReportedDeviceDesc
                if (fn_SetupDiGetDeviceProperty && fn_SetupDiGetDeviceProperty (hDevInfo, &DeviceInfoData, &DEVPKEY_Device_BusReportedDeviceDesc,
                                                                                &ulPropertyType, (BYTE*)szDesc, sizeof(szDesc), &dwSize, 0))
                    _tprintf (TEXT("    Bus Reported Device Description: \"%s\"\n"), szDesc);
        }

        pszToken = _tcstok_s (szDeviceInstanceID , TEXT("\\#&"), &pszNextToken);
        while(pszToken != NULL)
        {
            szVid[0] = TEXT('\0');
            szPid[0] = TEXT('\0');
            szMi[0] = TEXT('\0');
            for (j = 0; j < 3; j++) {
                if (_tcsncmp(pszToken, arPrefix[j], lstrlen(arPrefix[j])) == 0) {
                    switch(j) {
                        case 0:
                            _tcscpy_s(szVid, ARRAY_SIZE(szVid), pszToken);
                            break;
                        case 1:
                            _tcscpy_s(szPid, ARRAY_SIZE(szPid), pszToken);
                            break;
                        case 2:
                            _tcscpy_s(szMi, ARRAY_SIZE(szMi), pszToken);
                            break;
                        default:
                            break;
                    }
                }
            }
            if (szVid[0] != TEXT('\0'))
                _tprintf (TEXT("    vid: \"%s\"\n"), szVid);
            if (szPid[0] != TEXT('\0'))
                _tprintf (TEXT("    pid: \"%s\"\n"), szPid);
            if (szMi[0] != TEXT('\0'))
                _tprintf (TEXT("    mi: \"%s\"\n"), szMi);
            pszToken = _tcstok_s (NULL, TEXT("\\#&"), &pszNextToken);

            //VID and PID for the playstation Move.
            if( szVid[4] == TEXT('8') && 
                szVid[5] == TEXT('8') && 
                szVid[6] == TEXT('8') && 
                szVid[7] == TEXT('8') &&
                szPid[4] == TEXT('0') &&
                szPid[5] == TEXT('3') &&
                szPid[6] == TEXT('0') &&
                szPid[7] == TEXT('8'))
            {
                std::cout << "PlayStation Move Detected!" << std::endl;
                break;
            }
        }

    }

    return;
}

int main()
{
    int iQuit;
    ListUsbDevices();
    std::cin >> iQuit;

    return 0;
}

How come we need to define the FN_SetupDiGetDeviceProperty block of code first? And what does it acturly do? I thought that the SetupDiGetDeviceProperty function is part of the WDK so we can use it straight away??

Answer 1

typedef BOOL (WINAPI *FN_SetupDiGetDeviceProperty)(
  __in       HDEVINFO DeviceInfoSet,
  __in       PSP_DEVINFO_DATA DeviceInfoData,
  __in       const DEVPROPKEY *PropertyKey,
  __out      DEVPROPTYPE *PropertyType,
  __out_opt  PBYTE PropertyBuffer,
  __in       DWORD PropertyBufferSize,
  __out_opt  PDWORD RequiredSize,
  __in       DWORD Flags
);

The above code is defining FN_SetupDiGetDeviceProperty as a pointer to a function taking that (long) list of parameters and returning a BOOL. WINAPI is a macro specifying the calling convention (__stdcall, __cdecl etc.) of the function.

Later on in your code, the function pointer fn_SetupDiGetDeviceProperty is being conditionally set to either SetupDiGetDevicePropertyW or SetupDiGetDevicePropertyA depending on whether you’re compiling with the UNICODE macro defined or not.

There is actually no function named SetupDiGetDeviceProperty exported by the DLL. If you dig through the headers of the library you’re using you’ll find something like this:

#ifdef UNICODE
#define SetupDiGetDeviceProperty SetupDiGetDevicePropertyW
#else
#define SetupDiGetDeviceProperty SetupDiGetDevicePropertyA
#endif

So, when you call SetupDiGetDeviceProperty you’re actually calling one of the 2 variants (A/W) of the function.