return a char array from a function

[tnorton]

Hi all,

Need a little help here.

I am trying to return the MAC of a codec using the following function but cant work out how to convert the Buffer from char[5] to char as the return value.


Error 5 error C2440: 'return' : cannot convert from 'char [5]' to 'char' j:\Indigo Vision\COM\VBserial.dll\IVserial.cpp 194


Its probably obvious but I can seem to convert it


Tim Norton

char DisplayDeviceInfo( const VBDEVICEINFO *pDeviceInfo )
 
{
    VBMSRV_PLAYBACKINFO pbInfo;
    UINT nValue;
    int  nSize;
    char Buffer[5];
 
     sprintf(Buffer,
        "%02X:%02X:%02X:%02X:%02X:%02X\n",
        pDeviceInfo->macAddress.abMacAddr[ 0 ],
        pDeviceInfo->macAddress.abMacAddr[ 1 ],
        pDeviceInfo->macAddress.abMacAddr[ 2 ],
        pDeviceInfo->macAddress.abMacAddr[ 3 ],
       pDeviceInfo->macAddress.abMacAddr[ 4 ],
        pDeviceInfo->macAddress.abMacAddr[ 5 ]
        );
 
       return Buffer;
}
 

[weaknessforcats]

Your function is returning a char.

The name Buffer is a char*.

That's because the name of the array is the address of element 0.

You could change your function to return a char* but you would just crash again since you would return the address of a local variable.

The solution here is to have a char** argument and you allocate your Buffer on the heap using the char** argument:

void DisplayDeviceInfo( const VBDEVICEINFO *pDeviceInfo, char** Buffer )
 
{
    VBMSRV_PLAYBACKINFO pbInfo;
    UINT nValue;
    int  nSize;
 
    delete *Buffer;      //delete the current Buffer
    char* *Buffer = new char[5];  //allocate a new one
 
     sprintf(*Buffer,
        "%02X:%02X:%02X:%02X:%02X:%02X\n",
        pDeviceInfo->macAddress.abMacAddr[ 0 ],
        pDeviceInfo->macAddress.abMacAddr[ 1 ],
        pDeviceInfo->macAddress.abMacAddr[ 2 ],
        pDeviceInfo->macAddress.abMacAddr[ 3 ],
       pDeviceInfo->macAddress.abMacAddr[ 4 ],
        pDeviceInfo->macAddress.abMacAddr[ 5 ]
        );
 
}
 

[tnorton]

Thsnks for the response.
I will try that but there is something I iver looked mentioning that I think will impact on this.
I am creating a DLL that is returning the value to VB,
how do I get the charr** to output from the DLL?

May other public Functins all look like this
[code]ccp[
int __stdcall VbCleanup1()
bool __stdcall VbCloseDevice1(HANDLE m_hDevice)
bool __stdcall VbAuxChannelConnect1(HANDLE m_hDevice,const char *IPAddressSerial, VBAUXTYPE SerialPort, int Priority, bool Persistant, VBAUXCHANCALLBACK myCallback)

/CODE]

[Cucumber]

Thsnks for the response.
I will try that but there is something I iver looked mentioning that I think will impact on this.
I am creating a DLL that is returning the value to VB,
how do I get the charr** to output from the DLL?

May other public Functins all look like this
[code]ccp[
int __stdcall VbCleanup1()
bool __stdcall VbCloseDevice1(HANDLE m_hDevice)
bool __stdcall VbAuxChannelConnect1(HANDLE m_hDevice,const char *IPAddressSerial, VBAUXTYPE SerialPort, int Priority, bool Persistant, VBAUXCHANCALLBACK myCallback)

/CODE]

I never created a DLL for visual basic in C, but as far as I know visual basic uses BSTR strings rather than chars.

[tnorton]

Forgive my ignorence but what does that mean?

[weaknessforcats]

Forgive my ignorence but what does that mean?

It usually means your dll is a COM object that supports IDispatch and you address is returned in a VARIANT. If you support IDispatch, then your DLL object will appear in the Visual Basci Object Browser.

The BSTR that Cucumber mentioned is a Basic STRing. That is, it is a char array where the length of the array is at the beginning and it may contain any number of C-style strings separated by a \0. At the very end, the BSTR terminator is a \0\0.

You will need to read up on this.