<QtLogging> - Qt Logging Types

Macro Documentation

qCritical(const char *message, ...)

Calls the message handler with the critical message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

It exits if the environment variable QT_FATAL_CRITICALS is not empty.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

void load(const QString &fileName)
{
    QFile file(fileName);
    if (!file.exists())
        qCritical("File '%s' does not exist!", qUtf8Printable(fileName));
}

If you include <QtDebug>, a more convenient syntax is also available:

qCritical() << "Brush:" << myQBrush << "Other value:" << i;

A space is inserted between the items, and a newline is appended at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

Note: This macro is thread-safe.

See also qDebug(), qInfo(), qWarning(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.

qDebug(const char *message, ...)

Calls the message handler with the debug message message. If no message handler has been installed, the message is printed to stderr. Under Windows the message is sent to the console, if it is a console application; otherwise, it is sent to the debugger. On QNX, the message is sent to slogger2. This function does nothing if QT_NO_DEBUG_OUTPUT was defined during compilation.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.

Example:

qDebug("Items in list: %d", myList.size());

If you include <QtDebug>, a more convenient syntax is also available:

qDebug() << "Brush:" << myQBrush << "Other value:" << i;

With this syntax, the function returns a QDebug object that is configured to use the QtDebugMsg message type. It automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

Note: This macro is thread-safe.

See also qInfo(), qWarning(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.

qFatal(const char *message, ...)

Calls the message handler with the fatal message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2.

If you are using the default message handler this function will abort to create a core dump. On Windows, for debug builds, this function will report a _CRT_ERROR enabling you to connect a debugger to the application.

This function takes a format string and a list of arguments, similar to the C printf() function.

Example:

int divide(int a, int b)
{
    if (b == 0)                                // program error
        qFatal("divide: cannot divide by zero");
    return a / b;
}

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

See also qDebug(), qInfo(), qWarning(), qCritical(), qInstallMessageHandler(), and Debugging Techniques.

qInfo(const char *message, ...)

Calls the message handler with the informational message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the console, if it is a console application; otherwise, it is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_INFO_OUTPUT was defined during compilation.

If you pass the function a format string and a list of arguments, it works in similar way to the C printf() function. The format should be a Latin-1 string.

Example:

qInfo("Items in list: %d", myList.size());

If you include <QtDebug>, a more convenient syntax is also available:

qInfo() << "Brush:" << myQBrush << "Other value:" << i;

With this syntax, the function returns a QDebug object that is configured to use the QtInfoMsg message type. It automatically puts a single space between each item, and outputs a newline at the end. It supports many C++ and Qt types.

To suppress the output at runtime, install your own message handler using qInstallMessageHandler().

Note: This macro is thread-safe.

See also qDebug(), qWarning(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.

qWarning(const char *message, ...)

Calls the message handler with the warning message message. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. On QNX the message is sent to slogger2. This function does nothing if QT_NO_WARNING_OUTPUT was defined during compilation; it exits if at the nth warning corresponding to the counter in environment variable QT_FATAL_WARNINGS. That is, if the environment variable contains the value 1, it will exit on the 1st message; if it contains the value 10, it will exit on the 10th message. Any non-numeric value is equivalent to 1.

This function takes a format string and a list of arguments, similar to the C printf() function. The format should be a Latin-1 string.

Example:

void f(int c)
{
    if (c > 200)
        qWarning("f: bad argument, c == %d", c);
}

If you include <QtDebug>, a more convenient syntax is also available:

qWarning() << "Brush:" << myQBrush << "Other value:" << i;

This syntax inserts a space between each item, and appends a newline at the end.

To suppress the output at runtime, install your own message handler with qInstallMessageHandler().

Note: This macro is thread-safe.

See also qDebug(), qInfo(), qCritical(), qFatal(), qInstallMessageHandler(), and Debugging Techniques.