Code snippet: QLabel to show remote pixmap by URL

Perhaps one of the most often used widgets in Qt is QLabel. It is mainly used to display a plain text as well as rich one (which contains HTML markup). QLabel is also able to show graphics by passing QPixmap instance to it. But what if there is a need to display (using QLabel) a pixmap stored on remote server? There is no such "out of the box" functionality in QLabel. But it can be easily done. Here I want to show you how.

We just make a derivative class of QLabel and add only one new public method -- setRemotePixmap(const QString&) to let the label know that we want to display a remote graphics. Then the label composes HTTP GET request using QNetworkAccessManager class to retrieve the file. When the image is retrieved, it is showed up using setPixmap(const QPixmap&).

Let's see the source code.

QCryptographicHash: code snippet

  When the guys developing Qt applications find themselves in such a case when they need to obtain MD5 hash of a string or an array of bytes, the first thing most of them do is try to use the already implemented 3rd-party libraries like libxcrypt, OpenSSL and others. The talented ones try to get the output of 'md5sum' command.
  But the 'true' way is to use built-in tools: not everyone knows that Qt already has QCryptographicHash class which can help us. Let's see how:


QString password("our super secret password");
QByteArray hashed_password_ba(
     QCryptographicHash::hash(password.toAscii(),
                              QCryptographicHash::Md5));
/* Now 'md5_password' var contains
*  md5-hashed our super secret password 
*/
QString md5_password(hashed_password_ba.toHex().constData());

Very easy, isn't it? Apart from MD5, the class allows to generate MD4 and Sha1 hashes which may also be very helpful in some special cases.