Qt5 - C++11: 'This' cannot be implicitly captured in this context

Question

I am trying to pass the result of a qDebug() statement into a QTextEdit but without success because I am getting a compiler error of 'This' cannot be implicitly captured in this context and I have never got this error before.

Then output is coming after executing a QProcess and would like to show it on the QTextEdit I have below:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    startLidar();
    ui->textEditLidar->setText("[STATUS] NO PROCESS STARTED: ");
    ui->textEditGUI->setText("[STATUS] NO PROCESS STARTED: ");
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::startLidar()
{
    // Execution of the QProcess to make sure Lidar App Launcher opens:
    this->executeROSLidarApp = new QProcess(this);
    this->executeROSLidarApp->setProcessChannelMode(QProcess::MergedChannels);
    connect(this->executeROSLidarApp, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished),
            [script = this->executeROSLidarApp](int exitCode, QProcess::ExitStatus exitStatus){
            qDebug() << "[EXEC] FINISHED: " << exitCode << exitStatus;
            if(script->bytesAvailable() > 0) qDebug() << "[EXEC] buffered DATA:" << script->readAll();

            ui->textEditLidar->setText("would like to see the output of the exitCode and exitStatus"); // <-- error here

    });
    connect(this->executeROSLidarApp, &QProcess::errorOccurred, [script = this->executeROSLidarApp](QProcess::ProcessError error) {
            qDebug() << "[EXEC] error on execution: " << error << script->errorString();

            ui->textEditLidar->setText("would like to see the output of the error"); // <-- error here
    });
}

I think this is connected to the different C++ edition I am using. I have been using C++11 and it seems to be connected to a possible lambda function compilation error. I have been trying to research this error and came across this source , this additional source and everything seems to be leading to a mismatch between the different editions. In case needed I could also include my .pro file.

Thanks for shedding light on this issue and point to the right direction for solving this problem.

Answer 1

Your lambda does not capture this (as the error message tells you) but you're trying to access it (ui->textEditLidar->...)

Answer 2

Your lambda does not capture ui or this , so there's no way to call ui->textEditLidar->setText .

Change this

connect(this->executeROSLidarApp, &QProcess::errorOccurred, [script = this->executeROSLidarApp](QProcess::ProcessError error) {
        qDebug() << "[EXEC] error on execution: " << error << script->errorString();

        ui->textEditLidar->setText("would like to see the output of the error"); // <-- error here
});

to this

connect(this->executeROSLidarApp, &QProcess::errorOccurred, [this, script = this->executeROSLidarApp](QProcess::ProcessError error) {
        qDebug() << "[EXEC] error on execution: " << error << script->errorString();

        ui->textEditLidar->setText("would like to see the output of the error"); // <-- error here
});

or this

connect(this->executeROSLidarApp, &QProcess::errorOccurred, [ui, script = this->executeROSLidarApp](QProcess::ProcessError error) {
        qDebug() << "[EXEC] error on execution: " << error << script->errorString();

        ui->textEditLidar->setText("would like to see the output of the error"); // <-- error here
});