Error 5 error C2440: 'return' : cannot convert from...

tnorton · #1 24-Oct-2007, 07:00

c++ dll - return/convert to a string from a function that retunds char[]

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 or other string type as the return value.
This will be used in a DLL in a VB app. (Basically because my knowledge of C is very low)

The following code returns this error
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

CPP / C++ / C Code:

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;
}

fakepoo · #2 24-Oct-2007, 07:38

For starters, your function signature suggest that you wish to return a single char, not an array of char. Secondly, if you want to convert it to a string object, most strings will have a constructor that takes a char* (or char[]). Try

CPP / C++ / C Code:

return string(Buffer);

tnorton · #3 24-Oct-2007, 07:47

I had alreay tried that as it seemed logical but get this error
Error 5 error C2440: 'return' : cannot convert from 'std::basic_string<_Elem,_Traits,_Ax>' to 'char *' j:\Indigo Vision\COM\VBserial.dll\IVserial.cpp 198

these are the includes I have. Am I missing one?

CPP / C++ / C Code:

#include "StdAfx.h"
#include "IVserial.h"
#include <stdio.h>
#include <atlstr.h>

#include <string>   //just for testing
#include <cstring> //just for testing
using std::string;

CPP / C++ / C Code:

char* DisplayDeviceInfo( const VBDEVICEINFO *pDeviceInfo )
{
    VBMSRV_PLAYBACKINFO pbInfo;
	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 string(Buffer);

}

fakepoo · #4 24-Oct-2007, 07:50

You have to change your function to return a string, not a char*.

tnorton · #5 24-Oct-2007, 07:53

did that last night too but get this error, which I dont understand
Error 9 error LNK2019: unresolved external symbol "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl DisplayDeviceInfo(struct tagVBDEVICEINFO const *)" (?DisplayDeviceInfo@@YA?AV?$basic_string@DU?$char_ traits@D@std@@V?$allocator@D@2@@std@@PBUtagVBDEVIC EINFO@@@Z) referenced in function "char __stdcall Nortronics::GetMAC(char *)" (?GetMAC@Nortronics@@YGDPAD@Z) IVserial.obj

tnorton · #6 24-Oct-2007, 08:08

OK, I feel like an idiot now.
The second error wasfor a differnet function
sorry

fakepoo · #7 24-Oct-2007, 08:08

I can't really tell without looking at all of the code, but do the function signatures exactly match. In other words...

CPP / C++ / C Code:

// somewhere in the header
string DisplayDeviceInfo( const VBDEVICEINFO *pDeviceInfo );

// in the cpp file
string DisplayDeviceInfo( const VBDEVICEINFO *pDeviceInfo )
{
    VBMSRV_PLAYBACKINFO pbInfo;
	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 string(Buffer);
}

If that doesn't solve the problem, you may want to post your header file as well as the cpp file and I'll give it a better look.

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