WIndows MAPI unicode issue - windows

Question

It seems to me that MAPI (Windows Mail API) has issues with UTF8 (or maybe I did something wrong).
Code sample:
HMODULE m_hLib = LoadLibraryA("MAPI32.DLL");
if (m_hLib == NULL)
return SEND_MAIL_CANCELED;
LPMAPISENDMAIL SendMail;
SendMail = (LPMAPISENDMAIL) GetProcAddress(m_hLib, "MAPISendMail");
if (!SendMail)
return;
MapiFileDesc fileDesc;
ZeroMemory(&fileDesc, sizeof(fileDesc));
fileDesc.nPosition = (ULONG) -1;
fileDesc.lpszPathName = (LPSTR) filePath.toUtf8();
fileDesc.lpszFileName = (LPSTR) fileName.toUtf8();
MapiRecipDesc recipientData;
ZeroMemory(&recipientData, sizeof(recipientData));
recipientData.lpszName = (LPSTR) recipient.toUtf8();
recipientData.ulRecipClass = MAPI_TO;
MapiMessage message;
ZeroMemory(&message, sizeof(message));
message.ulReserved = CP_UTF8;
message.lpszSubject = (LPSTR) title.toUtf8();
message.nFileCount = 1;
message.lpFiles = &fileDesc;
message.nRecipCount = 1;
message.lpRecips = &recipientData;
int nError = SendMail(0, NULL, &message, MAPI_LOGON_UI | MAPI_DIALOG, 0);
title, filePath, fileName and recipient are all std::strings. As far as I know, UTF8 is compatible with ASCII (also NULL terminated), so its string can hold such values without any problems.
I'm converting to UTF8 from wstring in this way:
int requiredSize = WideCharToMultiByte(CP_UTF8, 0, data.c_str(), -1, 0, 0, 0, 0);
if(requiredSize > 0)
{
std::vector<char> buffer(requiredSize);
WideCharToMultiByte(CP_UTF8, 0, data.c_str(), -1, &buffer[0], requiredSize, 0, 0);
this->container.append(buffer.begin(), buffer.end() - 1);
}
container is a std::string object.

Answer 1

MAPISendMail() does not support UTF-8, only Ansi. If you need to send Unicode data, you have to use MAPISendMailHelper() on Windows 7 and earlier, or MAPISendMailW() on Windows 8 and later. This is clearly stated in the MAPISendMail() documentation.
On a side note, WideCharToMultiByte() includes the null terminator when you set the cchWideChar parameter to -1. As such, you are encoding and including that null terminator in your container data. You should instead set cchWideChar to the actual length of the string to avoid the null terminator completely:
int requiredSize = WideCharToMultiByte(CP_UTF8, 0, data.c_str(), data.length(), 0, 0, 0, 0);
if (requiredSize > 0)
{
std::vector<char> buffer(requiredSize);
WideCharToMultiByte(CP_UTF8, 0, data.c_str(), data.length(), &buffer[0], requiredSize, 0, 0);
container.append(buffer.begin(), buffer.end());
}
On http://msdn.microsoft.com/en-us/library/windows/desktop/dd296721.aspx it states "On Windows 7 and earlier: Use MAPISendMailHelper to send a message" but at the bottom of http://msdn.microsoft.com/en-us/library/windows/desktop/hh802867.aspx it states "Minimum supported" is Windows 8. Seems like contradictory information and therefore it's unclear whether MAPISendMailHelper is really for Windows 7 and earlier.