This example returns an array containing two cells: the book name and the sheet name contained in the argument FullName.

// Function:    SheetTest 
// Purpose:     Split a full sheet name into book and sheet name parts 
 
//{{XLP_SRC(SheetTest) 
    // NOTE - the FunctionWizard will add and remove mapping code here. 
    //    DO NOT EDIT what you see in these blocks of generated code!
IMPLEMENT_XLLFN3(SheetTest, SheetTest_4, SheetTest_12, "RC", "UC%", L"SheetTes"
    L"t", 0, L"FullName", 0, L"14", 0, L"Split a full sheet name into book and"
    L" sheet name parts", 0, L"No description provided\0", 0, 0, L"{SheetTest,"
    L",,Split a full sheet name into book and sheet name parts,14,1,132,U,{{0,"
    L"{FullName,String,0,,No description provided,,,,}}},{},3,,0,0}", 1)
CXlOper* SheetTest_Impl(CXlOper&, const CXlStringArg&);

extern "C" __declspec(dllexport)
LPXLOPER12 SheetTest_12(const XCHAR* FullName)
{
    XLL_FIX_STATE;
    CXlOper xloResult;
    CXlStringArg FullName__port(FullName);
    try {
        CXlStructuredExceptionHandler _seh_;
        xloResult.HandleResult(SheetTest_Impl(xloResult, FullName__port));
    }
    catch(const CXlRuntimeException& ex) {
        CXllApp::Instance()->DisplayException(xloResult, ex);
    }
    return xloResult.Ret12();
}
extern "C" __declspec(dllexport)
LPXLOPER4 SheetTest_4(const char* FullName)
{
    XLL_FIX_STATE;
    CXlOper xloResult;
    CXlStringArg FullName__port(FullName);
    try {
        CXlStructuredExceptionHandler _seh_;
        xloResult.HandleResult(SheetTest_Impl(xloResult, FullName__port));
    }
    catch(const CXlRuntimeException& ex) {
        CXllApp::Instance()->DisplayException(xloResult, ex);
    }
    return xloResult.Ret4();
}

CXlOper* SheetTest_Impl(CXlOper& xloResult, const CXlStringArg& FullName)
{
    // End of generated code 
//}}XLP_SRC

    CString bookName, sheetName;
    CXllApp::SplitSheetName(FullName, bookName, sheetName);

    xloResult.AllocArray(1, 2);
    xloResult.Cell(0, 0) = bookName;
    xloResult.Cell(0, 1) = sheetName;
    return xloResult.Ret();
}

Uses

CXllApp::SplitSheetName