DLL function not working in a VBA environment but working in Excel VBA

Question

I have the following function contained in a DLL I wrote (c++) that I debugged in Excel, and worked just fine:

float _stdcall ReturnT(LPCSTR FileName)
{

// Extracts the generic language string from the (importing BSTR  
// would import kanji or whatever) and converts it into a wstring
wstring str = CA2T(FileName);

// Sets the string to find as _t or _T followed by 2 or 3 digits and a subsequent _ or .
wregex ToFind(L"_[tT]\\d{2,3}(_|.)");
wsmatch TStr;

regex_search(str, TStr, ToFind);    // Now the wsmatch variable contains all the info about the matching
wstring T = TStr.str(0).erase(0, 2);    // Removes the first 2 characters
T.erase(T.end() - 1);               // Removes the last character

// Checks if T is 3 digits or not (2 digits) and eventually add a "."
wstring TVal = L"";
if (T.size() == 3)
{
    TVal += T.substr(0, 2) + L"." + T.substr(2, 3);
}
else if (T.size() == 2)
{
    TVal += T;
}

// Converts T string to a float
const float TValue = (float) _wtof(TVal.c_str());

return TValue;
}

If FileName is for example foo_T024.lol, this function correctly returns a float (in C++, or Single in VBA) with the value of 2.4 .

I call the function from VBA (both from Excel and the other environment) as:

Private Declare Function ReturnT Lib "[myDLLname]" (ByVal FileName As String) As Single

If I do the same from the other environment and use the function on the same string, I get an **ERROR** and sadly nothing else, because I can't debug (being this a proprietary application).

What could be the problem?

EDIT: I found out that this other environment is actually SAX, which is basically identical to VBA.

EDIT: I managed to link Visual Studio with the application, so I could check what's imported and what is wrong. FileName looks correctly imported, (I used also a VARIANT-input approach to see if that was the issue, which it wasn't) but I receive an error at this line:

wregex ToFind(L"_[tT]\\d{2,3}(\\_|\\.)");

The error is:

Unhandled exception at 0x75F0C54F in NSI2000.exe: Microsoft C++ exception: std::regex_error at memory location 0x0018E294.

And it stops by xthrow.cpp at this point:

#if _HAS_EXCEPTIONS

#include <regex>

_STD_BEGIN
_CRTIMP2_PURE _NO_RETURN(__CLRCALL_PURE_OR_CDECL _Xregex_error(regex_constants::error_type _Code))
    {   // report a regex_error
    _THROW_NCEE(regex_error, _Code);
    }                                     <--- Code stops here
_STD_END
 #endif /* _HAS_EXCEPTIONS */

EDIT: My VS version is 2013, the platformtoolset is the "Visual Studio 2013 - Windows XP (v120_xp)". My compiler version is: "Version 18.00.21005.1 for x64"

Answer 1

Turns out something was wrong with the string I've been importing. I do not understand what, since when I debugged the program, they looked fine. I solved by importing a SAFEARRAY of strings (which required me to change the whole function and the VBA code as well), whose BSTR value could be accessed as follows:

int _stdcall FilenameSort(LPSAFEARRAY* StringArray)
{
    // Fills a vector with the wstring values
    char** StrPtr = 0;
    long LowerBound = 0;  SafeArrayGetLBound(*StringArray, 1, &LowerBound);
    long UpperBound = 0;  SafeArrayGetUBound(*StringArray, 1, &UpperBound);
    const long Dimension = UpperBound - LowerBound;
    SafeArrayAccessData(*StringArray, reinterpret_cast<void**>(&StrPtr));

    BSTR element;
    vector<wstring> wstrArr;

    for (long i = 0; i <= Dimension; ++i)
    {
        SafeArrayGetElement(*StringArray, &i, &element);
        wstring ws(element, SysStringLen(element));
        wstrArr.push_back(ws);
    }

Having converted all the BSTRs in wstrings correctly, I could work with wregexs without any problem.