Can't append to a string in a COM Dll Strange behaviour - c++

Question

I am creating a Windows Shell Extension to add some options in the explorer context menu by making a COM dll but I get a strange problems with a vector.
I'm trying to append contents of a std::vector (member of the class) which contains paths into a std::wstring but at the end, only one path is added to the string. I know this is a problem with the vector itself because if I replace the vector by a local one instead of m_selectedFiles, it works.
Here is the code :
HRESULT FilesEncryptContextMenuHandler::InvokeCommand(CMINVOKECOMMANDINFO *pici) {
wchar_t filename[MAX_PATH] = {0};
GetModuleFileName((HMODULE)g_hInstance, filename, MAX_PATH);
std::wstring str = filename;
std::wstring exe = str.substr(0, str.find_last_of('\\')) + L"\\FilesEncrypt.exe";
std::basic_stringstream<wchar_t> ss;
for (std::vector<std::wstring>::iterator it = m_selectedFiles.begin(); it != m_selectedFiles.end(); ++it) {
MessageBox(NULL, it->c_str(), L"Test", MB_OK);
ss << *it << L" ";
}
std::wstring args = ss.str();
MessageBox(NULL, args.c_str(), L"Test", MB_OK);
args = args.substr(0, args.size() - 1);
ShellExecute(NULL, L"open", exe.c_str(), args.c_str(), NULL, SW_SHOWNA);
return S_OK;
}
Here, The MessageBox in the for loop is called multiple times with the paths but the second MessageBox only shows PATH1. For a reason I really don't know, the other elements in the vector are not appended.

Answer 1

It's because the line:
ss << *it << L" ";
places a NUL in the stream, the message box stops there. You will need to copy it->begin() to it->end()-1 to the stream.