Question

I am attempting to convert a LPTSTR variable to tstring(ie, wstring in a unicode application and string in ANSI).

How do I perform this conversion?

My code attempts to perform the conversion but it causes the error: “Debug Assertion Failed! Expression: invalid null pointer”:

#ifdef UNICODE  
#define tstring std::wstring  
#else  
#define tstring std::string  
#endif 

tstring TVManager::getDevicePropertyTEST(HDEVINFO hDevInfo, SP_DEVINFO_DATA deviceInfoData, DWORD flag)
{
    DWORD dataT      = 0;
    DWORD buffersize = 0;
    LPTSTR buffer    = NULL;

    while (!SetupDiGetDeviceRegistryProperty(hDevInfo,  &deviceInfoData, flag, &dataT,
                                             (PBYTE)buffer, buffersize, &buffersize))
    {
        if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
            // Change the buffer size.
            if (buffer) 
                LocalFree(buffer);
            buffer = (LPTSTR)LocalAlloc(LPTR, buffersize);
        }
        else {
            // Insert error handling here.
            debug_print_ex("Else happened:", buffer);
            break;
        }
    }

    tstring propertyValue = tstring(buffer); // ERROR OCCURS HERE

    if (buffer) 
        LocalFree(buffer);

    return propertyValue;
}

Answer 1

You’re passing a null pointer to std::basic_string<>‘s constructor – no good. Assuming you just want an empty string if buffer is null, then do the following:

tstring propertyValue;
if (buffer)
    propertyValue = buffer;