QT calling external program

QT Practical course ：

• QT Preliminary timer
• QT Signal and slot
• QT Multithreading practice
• QT File read and write

Source code address ： QT Call the external program

Call system instructions

For similar replication 、 Mobile and other functions , Obviously, the operating system provides more complete instructions .QT Provides QProcess class , Used to call system instructions , It's like C In language system equally .

for example , stay Windows Copy commands are also provided in copy, Then drag a button , Renamed as btnCopyFile, Then go to slot , add to click action

void MainWindow::on_btnCopyFile_clicked()
{
    
    QString oldName = QFileDialog::getOpenFileName(this," Please select a file ");
    QString newName = QFileDialog::getSaveFileName(this," Please enter filename ");
    QProcess cpPro(this);
    QString code = "copy";
    ui->txtContent->setText(code);
    QStringList para;
    para << oldName << newName;
    foreach(QString item, para)
        ui->txtContent->append(item);
    cpPro.start(code, para);
}

among ,cpPro It's just one. QProcess, Used in the final call cpPro.start(code,para), among code It's an instruction ready to execute , The format is QString;para It's a list of instructions , The type is QStringList, That is to say QList<QString>.

The effect is

The return value of the system instruction

QProcess The power of , It can not only execute the command line instructions of the system , It can also capture the return value of the command line . With ls Command as an example （ Of course ,Windows There is no self ls Of , You can use dir）

The effect is

The code is

void MainWindow::on_btnListFiles_clicked()
{
    
    QString folder = QFileDialog::getExistingDirectory(this," Please select a folder ");
    ui->lineTitle->setText(folder);
    QProcess cmd;
    cmd.start("dir",QStringList()<<folder);
    cmd.waitForStarted();
    cmd.waitForFinished();
    ui->txtContent->append(cmd.readAllStandardOutput());
}

Compared to the previous code , Two more wait, One read, seeing the name of a thing one thinks of its function , The former is used to wait for the command to start and complete , The latter is used to get the standard output of the command line .

This involves QProcess Life cycle of ：

1. waitForStarted()： Blocking , Until the external program starts
2. waitForReadyRead()： Blocking , Until the new data in the output channel is readable
3. waitForBytesWritten()： Blocking , Until the data in the input channel is written
4. waitForFinished()： Blocking , Until the end of the external program