Checking a port if it's in use/open

[squidge]

If the OP is given an answer to write a Firewall rule .. why isn't he given an answer on how Firewalls monitor ports? What I am reading here is the OP wants to write a Firewall like software and port 5500 is just an example.

1) Using a firewall rule is much simpler than writing software, and the OP might not have tried this avenue (Why write software if you don't have to? Your just making work for yourself for no reason)
2) Qt doesn't support writing firewall software, and we are guessing the OP is using Linux/Unix/BSD as his profile only says X-Windows, and nothing about MS-Windows.
3) An alternative way is given above that will work in Qt and be cross-platform, should the OP want to write software on his own.

[prof.ebral]

1) Using a firewall rule is much simpler than writing software, and the OP might not have tried this avenue (Why write software if you don't have to? Your just making work for yourself for no reason)

Because that is how innovations are made .. ?

Sutee, you need to look at the QNetwork classes.

[wysota]

Because that is how innovations are made .. ?

Reinventing the wheel is not an innovation, it's lack of proper research.

[squidge]

Because that is how innovations are made .. ?

This forum is dedicated to the Qt framework or minor other programming tasks. For help on writing a firewall, you should use a website more suited to the task, such as one dedicated to advanced topics of your chosen operating system, as different OSs have wildly different ways of interacting with the network layer.

Nothing in Qt will do anything like a typical firewall application. The only Qt-way of doing what the OP wants has already been described, but as pointed out, it is not the practical way to go about the task.

[wysota]

For help on writing a firewall, you should use a website more suited to the task, such as one dedicated to advanced topics of your chosen operating system, as different OSs have wildly different ways of interacting with the network layer.

The term "network layer" may be used incorrectly here You probably meant "networking stack" as most firewalls used today (especially on Windows systems) are most likely implemented in higher layers than the network layer of both the ISO model and the TCP/IP model. And to position ourselves in the situation described in this thread, a piece of software acting in userspace would reside in the most upper layer - the application layer (so each piece of data would have to go all the way up, decapsulated from each layer's headers until reaching the application listening on the port). Just my five cents...

[sutee84]

Thank you very much!