CODEWITHSUNDEEP
qtpointers
Frank
Frank

Reputation: 2696

Error passing pointer in QT

In QT have the following code that starts a thread to send out commands. The thread takes a char * and int as arguments. In the "run" I use the pointer that is given by the constuctor. The code is:

MyThread::MyThread(char * payld, int payld_size)
{
    payload_size = payld_size;
    payload_p = payld;
}

void MyThread::run()
{
    while(...)
    {
        sendCommand(payload_p, payload_size);
    }
}

Unfortunately this doesn´t work and my application crashes when I try to use thread.start(). But when I change it to:

MyThread::MyThread(char * payld, int payld_size)
{
    payload_size = payld_size;
    payload_p = payld;

    for(int i=0; i<payload_size; i++)
    {
        payload[i] =  payld[i];
    }
}

void MyThread::run()
{
    while(...)
    {
        sendCommand(payload, payload_size);
    }
}

The code does run and only crashes sometimes (looks pretty random to me). Can anybody Explain me why version one doesnt work and version two does? And any ideas on why the second code sometimes crashes? Could it be because the size of payload is not predefined (in the header file I defined it as 

char payload[];

When I define it as:

char payload[10];

it seems to work better, but it is annoying to test since the crashes are pretty random.

Upvotes: 1

Views: 153

Answers (1)

CapelliC
CapelliC

Reputation: 60014

instead of fiddling with char*, I would switch to QString (since you're using Qt). It takes a bit of learning, but it's almost mandatory to get code working smoothly in this framework. Then declare

QString payload;

and depending on sendCommand implementation, use one of the member functions QString to get the char*, like payload.toLatin1()

Upvotes: 2

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