使用Qt时如何打印控制台?

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?

我使用Qt4和c++来制作一些计算机图形的程序。我需要能够在运行时在控制台打印一些变量，而不是调试，但是即使我添加了这些库，cout似乎也不会起作用。有没有办法做到这一点?

12 个解决方案

#1

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

如果能够打印到stderr，您可以使用最初用于调试的以下流:

//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

尽管在注释中指出，如果定义QT_NO_DEBUG_OUTPUT，请记住qDebug消息。

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

如果你需要stdout，你可以试试这个(正如Kyle Strand指出的):

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

You could then call as follows:

你可以这样打电话:

qStdOut() << "std out!";

#2

I found this most useful:

我发现这最有用:

#include <QTextStream>

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

#3

Add this to your project file:

将此添加到项目文件中:

CONFIG += console

#4

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):

如果您想要一些像std::cout，写到您的应用程序的标准输出，您可以简单地做以下操作(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:

如果您想避免创建临时的QTextStream对象，请在以下评论中遵循Yakk的建议，创建一个函数来返回stdout的静态句柄:

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.

记住要定期刷新流，以确保输出实际上是打印出来的。

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):

请注意，上述技术也可以用于其他输出。然而，有更可读的方式来给stderr写信(credit to Goz和他的回答下面的评论):

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.

如果在编译时打开QT_NO_DEBUG_OUTPUT，则会关闭qDebug()。

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

(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不同于stderr的流中。)

---

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

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，带有终止\0字符。

#5

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

您想要打印哪些变量?如果你的意思是QStrings，那么这些需要转换成c字符串。试一试:

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

#6

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

它也有类似于prinft的语法，例如:

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

Very handy as well

非常方便的

#7

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

Go项目的属性-> Linker->系统->子系统，然后将其设置为控制台(/S)。

#8

#include <QTextStream>
...
qDebug()<<"Bla bla bla";

#9

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

包括iostream库和cout是std的一个对象:

#include <iostream>

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

#10

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.

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

#11

I tried all of the samples above:

我尝试了上面所有的样本:

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" );

All display except the qDebug() ones; Cannot find where QT_NO_DEBUG might be invoked. qDebug() worked fine for me but disappeared with ubuntu 17.10

除qDebug()之外的所有显示;找不到调用QT_NO_DEBUG的地方。qDebug()对我来说很好，但是在ubuntu 17.10中消失了。

Thanks

谢谢

#12

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!

好，在研究了几个关于如何从Qt到stdout的GUI输出消息的例子之后，我通过qDebug()和安装qInstallMessageHandler()，改进了一个工作独立的例子，将消息重定向到控制台。控制台将与GUI同时显示，如果必要的话可以隐藏。代码很容易与项目中的现有代码集成。这里是完整的示例，您可以随意使用它，只要您坚持使用GNU GPL v2。您必须使用某种形式的某种形式和一个主窗口，否则示例将运行，但可能在*退出时崩溃。注意:没有办法通过关闭按钮或菜单关闭，因为我已经测试了这些替代方案，并且应用程序会时不时地崩溃。如果没有关闭按钮，应用程序将是稳定的，您可以从主窗口关闭它。享受吧!

#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();
}