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使用Qt时如何打印到控制台

发布于 2024-09-26 21:52:23 字数 109 浏览 10 评论 0原文

我正在使用 Qt4 和 C++ 来制作一些计算机图形学程序。我需要能够在运行时在控制台中打印一些变量，而不是调试，但即使我添加了库，cout 似乎也不起作用。有办法做到这一点吗？

原文

I'm using Qt4 and C++ for making some programs in computer graphics. I need to be able to print some variables in my console at run-time, not debugging, but cout doesn't seem to work even if I add the libraries. Is there a way to do this?

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评论（12）

熊抱啵儿 2024-10-03 21:52:23

如果打印到 stderr 足够好，您可以使用以下最初用于调试的流：

#include<QDebug>

//qInfo is qt5.5+ only.
qInfo() << "C++ Style Info Message";
qInfo( "C Style Info Message" );

qDebug() << "C++ Style Debug Message";
qDebug( "C Style Debug Message" );

qWarning() << "C++ Style Warning Message";
qWarning( "C Style Warning Message" );

qCritical() << "C++ Style Critical Error Message";
qCritical( "C Style Critical Error Message" );

// qFatal does not have a C++ style method.
qFatal( "C Style Fatal Error Message" );

尽管如注释中所指出，但请记住，如果 QT_NO_DEBUG_OUTPUT ， qDebug 消息将被删除code> 已定义

如果您需要标准输出，您可以尝试类似的操作（正如凯尔·斯特兰德指出的那样）：

QTextStream& qStdOut()
{
    static QTextStream ts( stdout );
    return ts;
}

然后您可以按如下方式调用：

qStdOut() << "std out!";

If it is good enough to print to stderr, you can use the following streams originally intended for debugging:

#include<QDebug>

//qInfo is qt5.5+ only.
qInfo() << "C++ Style Info Message";
qInfo( "C Style Info Message" );

qDebug() << "C++ Style Debug Message";
qDebug( "C Style Debug Message" );

qWarning() << "C++ Style Warning Message";
qWarning( "C Style Warning Message" );

qCritical() << "C++ Style Critical Error Message";
qCritical( "C Style Critical Error Message" );

// qFatal does not have a C++ style method.
qFatal( "C Style Fatal Error Message" );

Though as pointed out in the comments, bear in mind qDebug messages are removed if QT_NO_DEBUG_OUTPUT is defined

If you need stdout you could try something like this (as Kyle Strand has pointed out):

QTextStream& qStdOut()
{
    static QTextStream ts( stdout );
    return ts;
}

You could then call as follows:

qStdOut() << "std out!";
回复 原文
单调的奢华 2024-10-03 21:52:23

我发现这个最有用：

#include <QTextStream>

QTextStream out(stdout);
foreach(QString x, strings)
    out << x << endl;

I found this most useful:

#include <QTextStream>

QTextStream out(stdout);
foreach(QString x, strings)
    out << x << endl;
回复 原文
你如我软肋 2024-10-03 21:52:23

将其添加到您的项目文件中：

CONFIG += console

Add this to your project file:

CONFIG += console
回复 原文
独孤求败 2024-10-03 21:52:23

写入 stdout

如果您想要将 std::cout 等内容写入应用程序的标准输出，您只需执行 以下内容 (归功于 CapelliC）：

QTextStream(stdout) << "string to print" << endl;

如果您想避免创建临时 QTextStream 对象，请按照 Yakk 在下面的注释中的建议创建一个函数以返回 static< stdout 的 /code> 句柄：

inline QTextStream& qStdout()
{
    static QTextStream r{stdout};
    return r;
}

...

foreach(QString x, strings)
    qStdout() << x << endl;

记住定期刷新流以确保实际打印输出。

写入 stderr

请注意，上述技术也可用于其他输出。然而，还有更易读的方式来写入 stderr （归功于 Goz 和下面的评论他的答案）：

qDebug() << "Debug Message";    // CAN BE REMOVED AT COMPILE TIME!
qWarning() << "Warning Message";
qCritical() << "Critical Error Message";
qFatal("Fatal Error Message");  // WILL KILL THE PROGRAM!

如果在编译时打开QT_NO_DEBUG_OUTPUT，则qDebug()将关闭。

（Goz 在评论中指出，对于非控制台应用程序，这些应用程序可以打印到与 stderr 不同的流。）

注意： 所有 Qt 打印方法 假设 const char* 参数是 ISO-8859-1 编码的字符串，以 \0 字符结尾。

Writing to stdout

If you want something that, like std::cout, writes to your application's standard output, you can simply do the following (credit to CapelliC):

QTextStream(stdout) << "string to print" << endl;

If you want to avoid creating a temporary QTextStream object, follow Yakk's suggestion in the comments below of creating a function to return a static handle for stdout:

inline QTextStream& qStdout()
{
    static QTextStream r{stdout};
    return r;
}

...

foreach(QString x, strings)
    qStdout() << x << endl;

Remember to flush the stream periodically to ensure the output is actually printed.

Writing to stderr

Note that the above technique can also be used for other outputs. However, there are more readable ways to write to stderr (credit to Goz and the comments below his answer):

qDebug() << "Debug Message";    // CAN BE REMOVED AT COMPILE TIME!
qWarning() << "Warning Message";
qCritical() << "Critical Error Message";
qFatal("Fatal Error Message");  // WILL KILL THE PROGRAM!

qDebug() is closed if QT_NO_DEBUG_OUTPUT is turned on at compile-time.

(Goz notes in a comment that for non-console apps, these can print to a different stream than stderr.)

NOTE: All of the Qt print methods assume that const char* arguments are ISO-8859-1 encoded strings with terminating \0 characters.

回复 原文
九局 2024-10-03 21:52:23

你想打印什么变量？如果您指的是 QString，则需要将其转换为 c-String。尝试：

std::cout << myString.toAscii().data();

What variables do you want to print? If you mean QStrings, those need to be converted to c-Strings. Try:

std::cout << myString.toAscii().data();
回复 原文
不美如何 2024-10-03 21:52:23

它还有类似于 printft 的语法，例如：

qDebug ("message %d, says: %s",num,str);

也非常方便

It also has a syntax similar to prinft, e.g.:

qDebug ("message %d, says: %s",num,str);

Very handy as well

回复 原文
末蓝 2024-10-03 21:52:23

转到项目的 Properties ->;链接器->系统-> SubSystem，然后将其设置为Console(/S)。

Go the Project's Properties -> Linker-> System -> SubSystem, then set it to Console(/S).

回复 原文
樱＆纷飞 2024-10-03 21:52:23

包含 iostream 库 并精确地说 cout 是 std 的对象怎么样：

#include <iostream>

std::cout << "Hello" << std::endl;

What about including iostream library and precise that cout is an object of std like this :

#include <iostream>

std::cout << "Hello" << std::endl;
回复 原文
飞烟轻若梦 2024-10-03 21:52:23

如果您使用 stdio 库打印到 stderr，则调用 fflush(stderr) 应该刷新缓冲区并获得实时日志记录。

If you are printing to stderr using the stdio library, a call to fflush(stderr) should flush the buffer and get you real-time logging.

回复 原文
岁月静好 2024-10-03 21:52:23

好吧，在研究了互联网上描述如何从 Qt 中的 GUI 向 stdout 输出消息的几个示例之后，我改进了一个通过 qDebug() 和安装 qInstallMessageHandler() 将消息重定向到控制台的独立工作示例。控制台将与 GUI 同时显示，并且可以在必要时隐藏。该代码很容易与项目中的现有代码集成。这是完整的示例，只要您遵守 GNU GPL v2 许可证，您可以随意以任何方式使用它。我认为你必须使用某种形式和一个 MainWindow - 否则示例将运行，但在被迫退出时可能会崩溃。注意：无法通过关闭按钮或菜单关闭来退出，因为我已经测试了这些替代方案，并且应用程序最终会时不时地崩溃。如果没有关闭按钮，应用程序将保持稳定，您可以从主窗口将其关闭。享受！

#include "mainwindow.h"
#include <QApplication>

//GNU GPL V2, 2015-02-07
#include <QMessageBox>
#include <windows.h>
#define CONSOLE_COLUMNS 80
#define CONSOLE_ROWS    5000
#define YOURCONSOLETITLE "Your_Console_Title"

typedef struct{

    CONSOLE_SCREEN_BUFFER_INFOEX conScreenBuffInfoEX;

    HANDLE con_screenbuf;
    HWND hwndConsole;
    HMENU consoleMenu ;
    QString consoleTitle;

    QMessageBox mBox;
    QString localMsg;
    QString errorMessage;
    WINBOOL errorCode;

} consoleT;

static consoleT *console;

BOOL WINAPI catchCTRL( DWORD ctrlMsg ){

        if( ctrlMsg == CTRL_C_EVENT ){

            HWND hwndWin = GetConsoleWindow();
               ShowWindow(hwndWin,SW_FORCEMINIMIZE);
        }

    return TRUE;
}

void removeCloseMenu(){

    int i;

    for( i = 0; i < 10; i++){

        console->hwndConsole = FindWindowW( NULL, console->consoleTitle.toStdWString().data());

        if(console->hwndConsole != NULL)
            break;
    }

    if( !(console->errorCode = 0) && (console->hwndConsole == NULL))
            console->errorMessage += QString("\nFindWindowW error: %1 \n").arg(console->errorCode);

    if( !(console->errorCode = 0) &&  !(console->consoleMenu = GetSystemMenu( console->hwndConsole, FALSE )) )
        console->errorMessage += QString("GetSystemMenu error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = DeleteMenu( console->consoleMenu, SC_CLOSE, MF_BYCOMMAND )))
           console->errorMessage += QString("DeleteMenu error: %1 \n").arg(console->errorCode);
}

void initialiseConsole(){

    console->conScreenBuffInfoEX.cbSize = sizeof(CONSOLE_SCREEN_BUFFER_INFOEX);
    console->consoleMenu = NULL;
    console->consoleTitle = YOURCONSOLETITLE;
    console->con_screenbuf = INVALID_HANDLE_VALUE;
    console->errorCode = 0;
    console->errorMessage = "";
    console->hwndConsole = NULL;
    console->localMsg = "";

    if(!(console->errorCode = FreeConsole()))
        console->errorMessage += QString("\nFreeConsole error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = AllocConsole()))
        console->errorMessage += QString("\nAllocConsole error: %1 \n").arg(console->errorCode);

    if( (console->errorCode = -1) && (INVALID_HANDLE_VALUE ==(console->con_screenbuf = CreateConsoleScreenBuffer( GENERIC_WRITE | GENERIC_READ,0, NULL, CONSOLE_TEXTMODE_BUFFER, NULL))))
        console->errorMessage += QString("\nCreateConsoleScreenBuffer error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = SetConsoleActiveScreenBuffer(console->con_screenbuf)))
        console->errorMessage += QString("\nSetConsoleActiveScreenBuffer error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = GetConsoleScreenBufferInfoEx(console->con_screenbuf, &console->conScreenBuffInfoEX)))
        console->errorMessage += QString("\nGetConsoleScreenBufferInfoEx error: %1 \n").arg(console->errorCode);

    console->conScreenBuffInfoEX.dwSize.X = CONSOLE_COLUMNS;
    console->conScreenBuffInfoEX.dwSize.Y = CONSOLE_ROWS;

    if(!(console->errorCode = SetConsoleScreenBufferInfoEx(console->con_screenbuf, &console->conScreenBuffInfoEX)))
       console->errorMessage += QString("\nSetConsoleScreenBufferInfoEx error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = SetConsoleTitleW(console->consoleTitle.toStdWString().data())))
        console->errorMessage += QString("SetConsoleTitle error: %1 \n").arg(console->errorCode);

    SetConsoleCtrlHandler(NULL, FALSE);
    SetConsoleCtrlHandler(catchCTRL, TRUE);

    removeCloseMenu();

    if(console->errorMessage.length() > 0){
        console->mBox.setText(console->errorMessage);
        console->mBox.show();
    }

}

void messageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg){


    if((console->con_screenbuf != INVALID_HANDLE_VALUE)){

        switch (type) {

        case QtDebugMsg:
            console->localMsg = console->errorMessage + "Debug: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtWarningMsg:
            console->localMsg = console->errorMessage + "Warning: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length() , NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtCriticalMsg:
            console->localMsg = console->errorMessage + "Critical: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtFatalMsg:
            console->localMsg = console->errorMessage + "Fatal: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            abort();
        }
    }
}



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

    qInstallMessageHandler(messageHandler);

    QApplication a(argc, argv);

    console = new consoleT();
    initialiseConsole();

    qDebug() << "Hello World!";

    MainWindow w;
    w.show();

    return a.exec();
}

Well, after studying several examples on the Internet describing how to output messages from a GUI in Qt to stdout, I have refined a working stand-alone example on redirecting messages to a console, via qDebug() and installing qInstallMessageHandler(). The console will be showed at the same time as the GUI and can be hidden if deemed necessary. The code is easy to integrate with existing code in your project. Here is the full sample and feel free to use it in any way as you like, as long as you adhere to the License GNU GPL v2. You have to use a form of some sort and a MainWindow I think - otherwise the sample will run, but probably crash when forced to quit. Note: there is no way to quit via a close button or a menu close because I have tested those alternatives and the application will crash eventually every now and then. Without the close button the application will be stable and you can close it down from the main window. Enjoy!

#include "mainwindow.h"
#include <QApplication>

//GNU GPL V2, 2015-02-07
#include <QMessageBox>
#include <windows.h>
#define CONSOLE_COLUMNS 80
#define CONSOLE_ROWS    5000
#define YOURCONSOLETITLE "Your_Console_Title"

typedef struct{

    CONSOLE_SCREEN_BUFFER_INFOEX conScreenBuffInfoEX;

    HANDLE con_screenbuf;
    HWND hwndConsole;
    HMENU consoleMenu ;
    QString consoleTitle;

    QMessageBox mBox;
    QString localMsg;
    QString errorMessage;
    WINBOOL errorCode;

} consoleT;

static consoleT *console;

BOOL WINAPI catchCTRL( DWORD ctrlMsg ){

        if( ctrlMsg == CTRL_C_EVENT ){

            HWND hwndWin = GetConsoleWindow();
               ShowWindow(hwndWin,SW_FORCEMINIMIZE);
        }

    return TRUE;
}

void removeCloseMenu(){

    int i;

    for( i = 0; i < 10; i++){

        console->hwndConsole = FindWindowW( NULL, console->consoleTitle.toStdWString().data());

        if(console->hwndConsole != NULL)
            break;
    }

    if( !(console->errorCode = 0) && (console->hwndConsole == NULL))
            console->errorMessage += QString("\nFindWindowW error: %1 \n").arg(console->errorCode);

    if( !(console->errorCode = 0) &&  !(console->consoleMenu = GetSystemMenu( console->hwndConsole, FALSE )) )
        console->errorMessage += QString("GetSystemMenu error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = DeleteMenu( console->consoleMenu, SC_CLOSE, MF_BYCOMMAND )))
           console->errorMessage += QString("DeleteMenu error: %1 \n").arg(console->errorCode);
}

void initialiseConsole(){

    console->conScreenBuffInfoEX.cbSize = sizeof(CONSOLE_SCREEN_BUFFER_INFOEX);
    console->consoleMenu = NULL;
    console->consoleTitle = YOURCONSOLETITLE;
    console->con_screenbuf = INVALID_HANDLE_VALUE;
    console->errorCode = 0;
    console->errorMessage = "";
    console->hwndConsole = NULL;
    console->localMsg = "";

    if(!(console->errorCode = FreeConsole()))
        console->errorMessage += QString("\nFreeConsole error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = AllocConsole()))
        console->errorMessage += QString("\nAllocConsole error: %1 \n").arg(console->errorCode);

    if( (console->errorCode = -1) && (INVALID_HANDLE_VALUE ==(console->con_screenbuf = CreateConsoleScreenBuffer( GENERIC_WRITE | GENERIC_READ,0, NULL, CONSOLE_TEXTMODE_BUFFER, NULL))))
        console->errorMessage += QString("\nCreateConsoleScreenBuffer error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = SetConsoleActiveScreenBuffer(console->con_screenbuf)))
        console->errorMessage += QString("\nSetConsoleActiveScreenBuffer error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = GetConsoleScreenBufferInfoEx(console->con_screenbuf, &console->conScreenBuffInfoEX)))
        console->errorMessage += QString("\nGetConsoleScreenBufferInfoEx error: %1 \n").arg(console->errorCode);

    console->conScreenBuffInfoEX.dwSize.X = CONSOLE_COLUMNS;
    console->conScreenBuffInfoEX.dwSize.Y = CONSOLE_ROWS;

    if(!(console->errorCode = SetConsoleScreenBufferInfoEx(console->con_screenbuf, &console->conScreenBuffInfoEX)))
       console->errorMessage += QString("\nSetConsoleScreenBufferInfoEx error: %1 \n").arg(console->errorCode);

    if(!(console->errorCode = SetConsoleTitleW(console->consoleTitle.toStdWString().data())))
        console->errorMessage += QString("SetConsoleTitle error: %1 \n").arg(console->errorCode);

    SetConsoleCtrlHandler(NULL, FALSE);
    SetConsoleCtrlHandler(catchCTRL, TRUE);

    removeCloseMenu();

    if(console->errorMessage.length() > 0){
        console->mBox.setText(console->errorMessage);
        console->mBox.show();
    }

}

void messageHandler(QtMsgType type, const QMessageLogContext &context, const QString &msg){


    if((console->con_screenbuf != INVALID_HANDLE_VALUE)){

        switch (type) {

        case QtDebugMsg:
            console->localMsg = console->errorMessage + "Debug: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtWarningMsg:
            console->localMsg = console->errorMessage + "Warning: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length() , NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtCriticalMsg:
            console->localMsg = console->errorMessage + "Critical: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            break;

        case QtFatalMsg:
            console->localMsg = console->errorMessage + "Fatal: " + msg;
            WriteConsoleW(console->con_screenbuf, console->localMsg.toStdWString().data(), console->localMsg.toStdWString().length(), NULL, NULL );
            WriteConsoleA(console->con_screenbuf, "\n--\n", 4, NULL, NULL );
            abort();
        }
    }
}



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

    qInstallMessageHandler(messageHandler);

    QApplication a(argc, argv);

    console = new consoleT();
    initialiseConsole();

    qDebug() << "Hello World!";

    MainWindow w;
    w.show();

    return a.exec();
}
回复 原文
终陌 2024-10-03 21:52:23

“构建并运行”>默认为“在终端中运行”--> 使用此命令启用

刷新缓冲区 --> fflush（标准输出）；
您还可以在 printf 或 cout 中使用“\n”。

"build & run" > Default for "Run in terminal" --> Enable

to flush the buffer use this command --> fflush(stdout);
you can also use "\n" in printf or cout.

回复 原文
桜花祭 2024-10-03 21:52:23

对于Qt5 QString必须进行转换，例如：

QString sResultText = lblLineEdit->text(); //<--text from QLineEdit
qInfo(sResultText.toUtf8().data()); //<--show converted result

For Qt5 QString must be converted, for example:

QString sResultText = lblLineEdit->text(); //<--text from QLineEdit
qInfo(sResultText.toUtf8().data()); //<--show converted result
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