Pop3

[DmitryNik]

I have to admit, that I don't understand something in "How does qDebug() << message work?". Apparently, at any one time, when we call qDebug() << something; something suppose to appear in the console, isn't it? But in this piece of code it will not work in a right way:

socket->write("LIST\r\n");
    QString str;
    while(socket->waitForReadyRead())
    {
        str = socket->readAll().data();
        qDebug() << str;
        qDebug() << str.length();
    }

socket->write("LIST\r\n");
    QString str;
    while(socket->waitForReadyRead())
    {
        str = socket->readAll().data();
        qDebug() << str;
        qDebug() << str.length();
    }

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I will not get the length of the string in the console. I tried to put a break-point. Yes, program will stop on that point, but once again there is no result on the screen for some reason. May be I need to include something in .pro file, besides QT += network. I don't know. Could you please explain me, what's going on behind the scene in qDebug() and why it will not show any results?

Thank you beforehand.

p.s. I consider the worst scenario, when message will be received by chunks. In this case either once the length will be shown or nothing at all.
p.p.s. I solved problem in this way:

socket->write("LIST\r\n");
    QByteArray arr;
    while(socket->waitForReadyRead())
    {
        arr.insert(arr.length(), socket->readAll());
        qDebug() << arr.data();
        qDebug() << "Length: " << arr.length();
        if(arr.endsWith(".\r\n"))
            break;
    }

socket->write("LIST\r\n");
    QByteArray arr;
    while(socket->waitForReadyRead())
    {
        arr.insert(arr.length(), socket->readAll());
        qDebug() << arr.data();
        qDebug() << "Length: " << arr.length();
        if(arr.endsWith(".\r\n"))
            break;
    }

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I got the right result. But why for the QString it doesn't work? I'm a bit confused. In the world of C++

std::cout

std::cout

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works perfectly. And we always can grab the right result for the string length... Honestly, I don't get it, how does qt interpret length-function for the QString...

[ChrisW67]

socket->write("LIST\r\n");
    QString str;
    while(socket->waitForReadyRead())
    {
        str = socket->readAll().data();
        qDebug() << str;
        qDebug() << str.length();
    }

socket->write("LIST\r\n");
    QString str;
    while(socket->waitForReadyRead())
    {
        str = socket->readAll().data();
        qDebug() << str;
        qDebug() << str.length();
    }

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You are retrieving a bunch of bytes into a QByteArray using QTcpSocket::readAll(). This may not be any sort of character data (although it should be for POP3) or a complete message. You then assume the content of the array is a C-style string (QByteArray::data()) and assign it to a QString. QString:perator=() runs it through fromAscii() which, depending what is actually in the data and the current codec settings, may do odd things to it. After that QString will report the number of characters in the QString.

On Windows you may need "CONFIG += console" to get console output when a debugger is not present.

[DmitryNik]

Thank you. Now I understand that. I presume, I can use only QByteArray, without QString.

BTW, I have one question: does qt have the class, which is related to readers-writers problem? Or we still need to write something like that:

while(true)
{
 mutex.acqure();
readcount++;
if(readcount == 1) mutex.acqure();
mutex.release();
 
//critical section
 
mutex.acqure();
readcount--;
if(readcount == 0) mutex.release();
mutex.release();
}

while(true)
{
 mutex.acqure();
readcount++;
if(readcount == 1) mutex.acqure();
mutex.release();

//critical section

mutex.acqure();
readcount--;
if(readcount == 0) mutex.release();
mutex.release();
}

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In C#, for instance, we have ReaderWriterLockSlim class, which reduce amount of code.

[ChrisW67]

Have a look at QMutex and the See Also list on that page.

[DmitryNik]

Thank you once again for clarifying.

p.s. yeah, that thread is not only about pop3 now =D