qt-C++笔记之QProcess

code review!

一.示例：QProcess来执行系统命令ls -l命令并打印出结果

代码

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    // 创建QProcess实例
    QProcess process;

    QString program_middle = "ls";
    QStringList middle_arguments;
    middle_arguments << "-l";
    // 启动进程执行命令
    process.start(program_middle, middle_arguments);

    // 等待进程结束
    process.waitForFinished();

    // 读取并打印进程的标准输出
    QByteArray result = process.readAllStandardOutput();
    qDebug() << result;

    return 0;
}

or

代码

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    // 创建QProcess实例
    QProcess process;
    // 启动进程执行命令
    process.start("ls", QStringList() << "-l");

    // 等待进程结束
    process.waitForFinished();

    // 读取并打印进程的标准输出
    QByteArray result = process.readAllStandardOutput();
    qDebug() << result;

    return 0;
}

说明

这个简短的示例中：

• 创建了QProcess对象。
• 使用start方法执行了ls -l命令。
• 使用waitForFinished方法等待命令执行完成（请注意，这会阻塞，直到外部命令执行完成）。
• 读取了命令的标准输出，并使用qDebug打印到控制台。

此代码省略了错误处理和信号/槽连接，适用于简单的同步命令执行。如果你想要异步处理或更复杂的错误处理，你需要采用第一个例子中的更详细的方法。

二.示例：QProcess来执行系统命令ls -l命令并打印出结果，代码进一步丰富

代码应该具有清晰的命名，详细的注释，以及适当的输出信息。下面是修改后的示例：

代码

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>

int main(int argc, char *argv[]) {
    QCoreApplication app(argc, argv);

    // 设置要执行的命令
    QString listCommand = "ls";
    // 设置命令的参数，以列出/home目录的详细内容
    QStringList listArguments;
    listArguments << "-l" << "/home";

    // 创建一个QProcess对象来运行外部命令
    QProcess directoryLister;

    // 在控制台输出即将执行的命令和参数
    qDebug() << "Executing command:" << listCommand << "with arguments" << listArguments;

    // 使用指定的命令和参数启动外部进程
    directoryLister.start(listCommand, listArguments);

    // 等待进程完成，最多等待2000毫秒
    bool isFinished = directoryLister.waitForFinished(2000);

    // 检查进程是否在规定时间内完成
    if (isFinished) {
        // 如果完成，读取命令的标准输出
        QByteArray output = directoryLister.readAllStandardOutput();
        // 在控制台输出命令的结果
        qDebug() << "Directory listing for /home:\n" << output;
    } else {
        // 如果没有完成，输出超时消息
        qDebug() << "The process did not finish within the specified 2 seconds.";
    }

    // 获取并输出进程的退出码
    int exitCode = directoryLister.exitCode();
    qDebug() << "The process exited with code:" << exitCode;

    return 0;
}

在这个修改后的代码中：

• 变量app代替了a，表示这是一个应用程序的实例。
• 变量listCommand和listArguments直观地表示了将被执行的命令及其参数。
• 对象directoryLister表示一个能够列出目录内容的进程。
• 注释详细描述了代码的每一个部分，帮助理解每一行代码的作用。
• 输出信息采用了更加清晰和教育性的语言，适合教科书风格。

三.示例：使用 QProcess 在 Qt 中执行 Bash 脚本并处理参数

1.运行

2.文件结构

3.cmd.sh

#!/bin/bash
# 这个脚本接受一个目录作为参数，并列出其内容

DIR=$1

if [ -z "$DIR" ]; then
    echo "Usage: $0 <directory>"
    exit 1
fi

ls $DIR

4.main.cpp

代码

#include <QCoreApplication>
#include <QDebug>
#include <QProcess>

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    // 创建 QProcess 实例
    QProcess process;

    // 脚本文件的路径
    QString scriptPath = "/home/user/qt_cpp_test/qt_test/cmd.sh";

    // 获取目录参数
    QString directory = "/home/user/qt_cpp_test/qt_test";

    // 运行脚本并传递参数
    process.start(scriptPath, QStringList() << directory);

    // 等待进程结束
    if (!process.waitForFinished()) {
        qDebug() << "The process failed to finish.";
        return 1;
    }

    // 获取进程的输出
    QByteArray output = process.readAll();

    // 打印输出
    qDebug() << output;

    return a.exec();
}

5.qt_test.pro

QT += widgets core
TARGET = qt_test
TEMPLATE = app
SOURCES += main.cpp

四.ChatGPT讲解

QProcess is a class provided by the Qt framework to start external programs and communicate with them. It can be used to start, terminate, and communicate with external programs using standard input/output or through specific channels.

Here’s an overview of how you might use QProcess in a Qt application:

Including QProcess

Before using QProcess, you need to include the QProcess header:

#include <QProcess>

Creating a QProcess Object

You can create a QProcess object like any other object in Qt:

QProcess *process = new QProcess(parent);

The parent is a pointer to a parent QObject, which takes ownership of the QProcess object, ensuring that it will be deleted when the parent is.

Starting a Process

You can start a process by calling the start method, providing the command and arguments to run:

process->start("executable", QStringList() << "arg1" << "arg2");

Or if you just need to execute a command without arguments:

process->start("executable");

Reading Output

You can read the standard output and error of the process:

QObject::connect(process, &QProcess::readyReadStandardOutput, [=]() {
    QByteArray standardOutput = process->readAllStandardOutput();
    // Process standard output here
});

QObject::connect(process, &QProcess::readyReadStandardError, [=]() {
    QByteArray standardError = process->readAllStandardError();
    // Process standard error here
});

Writing to the Process

You can write to the standard input of the process:

process->write("input data");

Checking if the Process is Running

You can check if the process is still running:

if (process->state() == QProcess::Running) {
    // Process is running
}

Waiting for the Process to Finish

You can wait synchronously for the process to finish:

process->waitForFinished(); // Waits until the process has finished

Terminating the Process

You can terminate the process:

process->terminate(); // Sends a terminate signal

Or kill the process:

process->kill(); // Kills the process immediately

Getting the Exit Status

Once the process has finished, you can get the exit status:

int exitCode = process->exitCode();
QProcess::ExitStatus exitStatus = process->exitStatus();

Example Usage

Here’s a simple example of using QProcess to run a command and print its output:

#include <QCoreApplication>
#include <QProcess>
#include <QDebug>

int main(int argc, char *argv[]) {
    QCoreApplication a(argc, argv);

    QProcess process;
    process.start("ls", QStringList() << "-l" << "/");

    if (!process.waitForStarted()) // Default timeout is 30 seconds
        return 1;

    if (!process.waitForFinished()) // Default timeout is 30 seconds
        return 2;

    qDebug() << process.readAllStandardOutput().trimmed();

    return a.exec();
}

This example runs the ls -l / command, which lists the contents of the root directory in a detailed format, then prints the output. Remember that the waitForStarted() and waitForFinished() methods are blocking calls; in a GUI application, you would typically connect the finished() signal to a slot to handle the process completion asynchronously.