Using QThread , Signal() , Slot() So GUI won't freeze

__d4ve__

I have error with :

pcap_loop(handle, NUM_PACKETS_TO_CAPTURE, packet_handler, nullptr);

the error :
C:\Users\Dave\Desktop\C++ Exercises\Qt Creator Projects\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:88: error: Reference to non-static member function must be called

full code here : Qt Packet Viewer Code

__d4ve__

@__d4ve__

Sum up of all the errors :


\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:55: error: C3861: 'update_gui': identifier not found

\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:88: error: C3867: 'workerobject::packet_handler': non-standard syntax; use '&' to create a pointer to member

\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:55: error: Use of undeclared identifier 'update_gui'

\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:88: error: Reference to non-static member function must be called

jsulm

@__d4ve__ said in Using QThread , Signal() , Slot() So GUI won't freeze:

\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:55: error: C3861: 'update_gui': identifier not found

Please show the code which causes this error...

__d4ve__

@jsulm
full code here : Qt Packet Viewer Code

seems that workerobject.cpp does the error

jsulm

@__d4ve__ Sorry, but I'm not going to search in that link for relevant parts. You can simply post the code (and only that code) which causes this errors...

__d4ve__

@jsulm
The error occurs with packet_handler & pcap_loop(handle, NUM_PACKETS_TO_CAPTURE, packet_handler, nullptr);
which is calling it

void packet_handler(u_char* user_data, const struct pcap_pkthdr* packet_header, const u_char* packet_data)
{
    std::stringstream packetInfo;

    // Add packet information to the stringstream
    packetInfo << std::endl;
    packetInfo << "Packet Information:" << std::endl;
    packetInfo << "Capture Length: " << std::setw(5) << packet_header->caplen << std::endl;
    packetInfo << "Packet Length: " << std::setw(5) << packet_header->len << std::endl;
    packetInfo << "Packet Data:" << std::endl;

    // Print packet data as hexadecimal and ASCII
    int byte_count = 0;
    for (unsigned int i = 0; i < packet_header->caplen; i++)
    {
        packetInfo << std::hex << std::setfill('0') << std::setw(2) << static_cast<int>(packet_data[i]) << " ";
        byte_count++;

        // Add extra space after every 8 bytes for better readability
        if (byte_count % 8 == 0)
            packetInfo << " ";

        // Add newline after every 16 bytes and print ASCII representation
        if (byte_count % 16 == 0)
        {
            packetInfo << "| ";
            for (unsigned int j = i - 15; j <= i; j++)
            {
                if (packet_data[j] >= 32 && packet_data[j] <= 126)
                    packetInfo << static_cast<char>(packet_data[j]);
                else
                    packetInfo << ".";
            }
            packetInfo << std::endl;
        }
    }

    std::string packetInfoString = packetInfo.str();
    QString packetInfoQString = QString::fromStdString(packetInfoString);

    QMutexLocker locker(&Mutex);
    std::cout << packetInfoString << std::endl;
   // emit packetCaptured(packetInfoQString);

    emit update_gui(packetInfoQString);
}

// loop through packets with choosen device ---- should add variable device
// The pcap_loop starter // in current stat device name need to be inputed
void workerobject::packet_looper()
{
    //QString selectedDev_qt; // Initialize it with the selected device name

    char errbuf[PCAP_ERRBUF_SIZE];
    pcap_if_t* alldevs = nullptr;
    pcap_if_t* selectedDev = nullptr;

    // Iterate over the list of interfaces and find the selected adapter
    for (pcap_if_t* dev = alldevs; dev != nullptr; dev = dev->next)
    {
        if (selectedDev_qt == dev->description)
        {
            selectedDev = dev;
            break;
        }
    }

    pcap_t* handle = pcap_open_live(selectedDev->name, BUFSIZ, 1, 1000, errbuf);
    if (handle == nullptr)
    {
        std::cerr << "Error opening interface for packet capture: " << errbuf << std::endl;
        pcap_freealldevs(alldevs);
        return; // Stop further execution if opening handle fails
    }

    QMutexLocker unlock(&Mutex);

    pcap_loop(handle, NUM_PACKETS_TO_CAPTURE, packet_handler, nullptr);

    // Close the packet capture handle
    pcap_close(handle);

    // Free the allocated memory for the interface list
    pcap_freealldevs(alldevs);
}

JonB

@__d4ve__
Sorry, what does "which is calling it" have anything to do with error? It is a compiler error for an undefined identifier.

What are lines #55 and #88 in workerobject.cpp? That is what we need to know!

If it errors on the line

emit update_gui(packetInfoQString);

you show above (but I only see one occurrence, how can that be both lines?) then update_gui() is not declared to the compiler at that point.

__d4ve__

@JonB
pcap_loop calls packet_handler -> emits update_gui

JonB

@JonB said in Using QThread , Signal() , Slot() So GUI won't freeze:

What are lines #55 and #88 in workerobject.cpp? That is what we need to know!

I give up and am out....

__d4ve__

I'm wondering if there is a better way to accomplish this task maybe using Tins .. but that's and issue by itself

Pl45m4

@__d4ve__ said in Using QThread , Signal() , Slot() So GUI won't freeze:

I'm wondering if there is a better way to accomplish this task maybe using Tins

How should this change something? It doesn't matter what lib you use, whether it's pcap, tins or packet sniffer 9000. If you want to keep your GUI responsive while using a synchronous library or function, you have to move it to a different thread.

Threading in general is a "not-so-easy" task, esp. with limited programming knowledge, but IMO a Worker-Thread is one of the easier approaches and it matches your requirements as well.

Read about how it works (in this topic are already plently of links) and be aware of what you really want to do (what function you want to run? what data should be send from where to where?... etc.)

__d4ve__

@Pl45m4

The task is keep GUI responsive , and yes you are right we achieved at this point the threading stuff the issue now have changed into running pcap_loop() which isn't working because it requires static function and I use non-static function

Pl45m4

@__d4ve__ said in Using QThread , Signal() , Slot() So GUI won't freeze:

which isn't working because it requires static function and I use non-static function

This is probably not the reason behind this issue...
I can only repeat what @JonB and others have said...
Look at the lines 55 and 88 and check what's written there or post it here. Because it's a pain to check your linked archieve when you have the code right in front of you. So probably nobody will dig through your whole project to find these two or more lines which will produce your current error.

__d4ve__

@Pl45m4

line 55 :

emit update_gui(packetInfoQString);

line 88 :

pcap_loop(handle ,NUM_PACKETS_TO_CAPTURE ,packet_handler , nullptr);

jsulm

@__d4ve__ said in Using QThread , Signal() , Slot() So GUI won't freeze:

emit update_gui(packetInfoQString);

Now, look at the first error message:
"\Project 1 - Network Packet GUI\Packet_Capture_GUI\workerobject.cpp:55: error: C3861: 'update_gui': identifier not found"

It tells you that update_gui is not known. Did you declare update_gui as signal in that class?

__d4ve__

@jsulm

Yes,

signals:
    void update_gui(QString packetInfoQString);
};

The issue is here : pcap_loop got call back function named packet_handle - this function emit update_gui

but the problem here that pcap_loop requires static function , while packet_handle can't be static function

try to run the project that's very short code

JonB

@__d4ve__
If you mean that signal update_gui() is a member of MainWindow then you won't be able to call it via

WorkerObject* wo=qobject_cast<WorkerObject*>(user_data);
assert(wo);
wo->update_gui(...);

You presumably need the signal defined somewhere accessible from WorkerObject and then a slot in MainWindow to receive the signal from the worker object.

Get the principle suggested by @mpergand working.

Pl45m4

@__d4ve__ said in Using QThread , Signal() , Slot() So GUI won't freeze:

signals:
void update_gui(QString packetInfoQString);
};

Where is this signal defined?

In the code snippet you've posted here, you have a function called
(I dont know if this is still your current code...)

void workerobject::packet_looper()
{ .... }

so one can assume it's a part of your workerobject.cpp file.
Above that code there is

void packet_handler(u_char* user_data, const struct pcap_pkthdr* packet_header, const u_char* packet_data)
{
    // .....
    emit update_gui(packetInfoQString);
}

Are you aware that packet_handler when written like that, is not a member of any class? It's defined as global function and there it probably wont recognize what update_gui is.
The same applies, when trying to emit that signal from somewhere else other than where it was defined.

SGaist

To add to my fellows, it's typically a good case for the use of invokeMethod.