Works On Windows/Fails On Linux?

//-------------------------------------------------------------------------------------------------
bool Logic::CheckSelectedLettersForWord(void)
{
char filename[256];
char *base_path = SDL_GetBasePath();
std::string letterASCII;
int numberOfSelectedLetters = 0;
std::string userWord;
bool returnValue = false;

    if (SelectedLetterPlayfieldX[2] == -1 && SelectedLetterPlayfieldY[2] == -1)  return(returnValue);

    int letter = 0;
    while (letter < 11 && SelectedLetterPlayfieldX[letter] != -1 && SelectedLetterPlayfieldY[letter] != -1)
    {
        numberOfSelectedLetters++;

        letterASCII = (char)(Playfield[ SelectedLetterPlayfieldX[letter] ][ SelectedLetterPlayfieldY[letter] ] + 96);
        userWord += letterASCII;

        letter++;
    }

    strcpy(filename, base_path);
    strcat(filename, "data/dictionary/");
    int firstLetterASCII = ('A' + Playfield[ SelectedLetterPlayfieldX[0] ][ SelectedLetterPlayfieldY[0] ] - 1);
    char firstLetter[2];
    sprintf(firstLetter, "%c", firstLetterASCII);
    strcat( filename, firstLetter );
    strcat(filename, "-Words.txt");

    std::stringstream ss;
    GetDataFromFile(filename, ss);

    std::string data;
    while ( std::getline(ss, data) )
    {
        if (userWord == data) // <-- Works on Windows, fails on Linux?
        {
            returnValue = true;
            break;
        }
    }

    return(returnValue);
}

//-------------------------------------------------------------------------------------------------