how to use cat command in QProcess

[renjithmamman]

i have a file in the project dirictory. i wnt to print it using qprocess

i tried like this but not working

void RptPrintBarCodeDlg::pbnOk_clicked()
{
    QString line;
    line="hello world";
    QFile file("print.txt");
    if ( file.open( IO_WriteOnly ) ) 
    {
        QTextStream stream( &file );
        stream<<line;
        file.close();
        QProcess *printbarcode = new QProcess(this);
        printbarcode->setWorkingDirectory(QDir::current());
        printbarcode->addArgument("cat");
        printbarcode->addArgument("print.txt");
        printbarcode->addArgument(">");
        printbarcode->addArgument("/dev/lp0");
 
        if(!printbarcode->start())
        {
            QMessageBox::information(this,"Error", "process not started" ,"Ok");
        }
    }
    else
    {
        QMessageBox::information(this,"Error", "File is not opened" ,"Ok");
 
    }
}

void RptPrintBarCodeDlg::pbnOk_clicked()
{
    QString line;
    line="hello world";
    QFile file("print.txt");
    if ( file.open( IO_WriteOnly ) ) 
    {
        QTextStream stream( &file );
        stream<<line;
        file.close();
        QProcess *printbarcode = new QProcess(this);
        printbarcode->setWorkingDirectory(QDir::current());
        printbarcode->addArgument("cat");
        printbarcode->addArgument("print.txt");
        printbarcode->addArgument(">");
        printbarcode->addArgument("/dev/lp0");
        
        if(!printbarcode->start())
        {
            QMessageBox::information(this,"Error", "process not started" ,"Ok");
        }
    }
    else
    {
        QMessageBox::information(this,"Error", "File is not opened" ,"Ok");

    }
}

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can anybody help me

[wysota]

You can't use ">" and alike in QProcess. They are interpreted by the shell and QProcess doesn't use a shell so all those <, >, |, & etc. are not interpreted.

Can't you just read the file and write it to the printer or even just copy it to the printer directly?

QUrlOperator *op = new QUrlOperator();
op->copy( "print.txt", "/dev/lp0" );

QUrlOperator *op = new QUrlOperator();
op->copy( "print.txt", "/dev/lp0" );

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or

QFile fr("print.txt");
QFile pr("/dev/lp0");
if(fr.open(IO_ReadOnly) && pr.open(IO_WriteOnly)){
    while(!fr.atEnd()){
        pr.putch(fr.getch()); // this is so crude!
    }
}

QFile fr("print.txt");
QFile pr("/dev/lp0");
if(fr.open(IO_ReadOnly) && pr.open(IO_WriteOnly)){
    while(!fr.atEnd()){
        pr.putch(fr.getch()); // this is so crude!
    }
}

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[fullmetalcoder]

what about using system(const char *) ???

[yop]

what about using system(const char *) ???

Not a good choice IMHO as:
a) You don't control the process
b) The event loop freezes until system(...) returns

QUrlOperator *op = new QUrlOperator();
op->copy( "print.txt", "/dev/lp0" );

QUrlOperator *op = new QUrlOperator();
op->copy( "print.txt", "/dev/lp0" );

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Wow this is beautiful, I used the second approach (the QFile("/dev/lp0") one) in a seperate thread to send data to a printer (though I used writeBlock()), but this is just beautiful, if I find a chance I'll use it as well

[dec0ding]

Please note that QProcess does not emulate a shell. This means that QProcess does not do any expansion of arguments: a '*' is passed as a '*' to the program and is not replaced by all the files, a '$HOME' is also passed literally and is not replaced by the environment variable HOME and the special characters for IO redirection ('>', '|', etc.) are also passed literally and do not have the special meaning as they have in a shell.

There is QByteStream or any Q*Stream class for those needs