editBox 过滤特定字符

void RegisterLayer::editBoxReturn(CCEditBox* editBox){    // 安全检查~    if (!editBox)    {        return;    }    string text = editBox->getText();    if (text.length() <= 0)    {        return;    }    // 过滤非法字符~    stringstream strStream;    for (int i = 0; i < text.length(); i ++)    {        unsigned char ch = text.at(i);        if ((ch >= 'a' && ch <= 'z') ||            (ch >= 'A' && ch <= 'Z') ||            (ch >= '0' && ch <= '9'))        {            strStream << ch;        }    }    string strResult = strStream.str();    editBox->setText(strResult.c_str());}