wstring to wchar_t conversion

I am using Namedpipes communication(C++) to transfer data between two processes. For the sake of comfort, I am using wstring to transfer the data and everything is fine at the transfer end. I am not able to receive the total data on the receiving end. The following is the transfer end code.

wstringstream send_data;        
send_data << "10" << " " << "20" << " " << "30" << " " << "40" << " " << "50" << " " << "60" << "\0" ;
DWORD numBytesWritten = 0;
result = WriteFile(
    pipe, // handle to our outbound pipe
    send_data.str().c_str(), // data to send
    send_data.str().size(), // length of data to send (bytes)
    &numBytesWritten, // will store actual amount of data sent
    NULL // not using overlapped IO
);

The following is the receiving end code.

wchar_t buffer[128];
DWORD numBytesRead = 0;
BOOL result = ReadFile(
    pipe,
    buffer, // the data from the pipe will be put here
    127 * sizeof(wchar_t), // number of bytes allocated
    &numBytesRead, // this will store number of bytes actually read
    NULL // not using overlapped IO
);

if (result) {
    buffer[numBytesRead / sizeof(wchar_t)] = '\0'; // null terminate the string
    wcout << "Number of bytes read: " << numBytesRead << endl;
    wcout << "Message: " << buffer << endl;

}

The result in buffer contains only 10 20 30 Can someone please explain me why the data is truncated.