What is the meaning of below if condition?

Question

i cannot understand below if condition. if anyone know about it then please help me to understand it.

foreach(QNetworkInterface netInterface, QNetworkInterface::allInterfaces())
{
     if(!(netInterface.flags() & netInterface.IsLoopBack))
     {
          qDebug()<<netInterface.humanReadableName();
          qDebug()<<netInterface.hardwareAddress();
     }
}

Answer 1

First lets start with the simple part: The logical negation operator !.

For any logical operation, the ! reverses the status of that operation. So !true is false, and !false is true.

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netInterface.IsLoopBack is the value of a single bit.

netInterface.flags() returns a set of bits.

netInterface.flags() & netInterface.IsLoopBack checks if the specific bit netInterface.IsLoopBack is in the set returned by netInterface.flags().

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Now putting it together, the result of netInterface.flags() & netInterface.IsLoopBack is an integer value. If the bit is in the set then it's non-zero.

In C++ all non-zero integer values is considered "true".

Applying the ! operator on this value reverses the condition.

So the condition !(netInterface.flags() & netInterface.IsLoopBack) will be true is the bit is not in the set.

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Lastly a bit of context: The loop iterates over all network interfaces on the local system.

If an interface is not a loopback interface (the address 127.0.0.1 is a loopback address) then the name and address of the interface is printed.

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Addendum: All of this could have been figured out relatively easy by reading some decent C++ books for the operators. And reading the documentation for QNetworkInterface::flags() and enum QNetworkInterface::InterfaceFlag.