CODEWITHSUNDEEP
qtqprocess
Something Different
Something Different

Reputation: 729

QProcess read and write

I am trying to read and write from a qprocess right now. I made a little test program that takes input and redisplays it on the screen in a loop. Here is my code from Qt

  QString path = "./test";

        tcd = new QProcess(this);
        QStringList args;
        args << "";
        tcd->start(path,args);

        if(!tcd->waitForStarted(3000))
        {
            stdoutput->append("<h1><font color=red>There was a problem starting the software, please try running the program again.</font></h1>");

        }
        tcd->write("hello\n");
        tcd->write("hello\n");
        tcd->write("hello\n");
        tcd->write("hello\n");
        //tcd->write("quit\n");

QObject::connect(tcd, SIGNAL(readyReadStandardOutput()), this, SLOT(appendTextBox()));

This won't work unless I send that last quit command (which terminates my test program).

Here's my read command:

void TCD2_GUI::appendTextBox(){
    stdoutput->append("new output available: \n");
    QByteArray newData = tcd->readAllStandardOutput();
    stdoutput->append(QString::fromLocal8Bit(newData));
}

if I send quit, I will get all the output from the program at once, including everything I have sent it.

What am I doing wrong here?

As per request, here is the code from the program:

int main(int argC[], char* argV[]){
    printf("Welcome!\n");
    char* input = malloc(160);
    gets(input);

    while(strcmp(input,"quit") != 0)
    {
        printf("Got input %s\n", input);
        gets(input);

    }

}

Upvotes: 2

Views: 6661

Answers (1)

ctd
ctd

Reputation: 1793

From the doc:

Certain subclasses of QIODevice, such as QTcpSocket and QProcess, are asynchronous. This means that I/O functions such as write() or read() always return immediately, while communication with the device itself may happen when control goes back to the event loop. QIODevice provides functions that allow you to force these operations to be performed immediately, while blocking the calling thread and without entering the event loop.

...

waitForBytesWritten() - This function suspends operation in the calling thread until one payload of data has been written to the device.

...

Calling these functions from the main, GUI thread, may cause your user interface to freeze.

link

Upvotes: 1

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