Qint64

[Aide Broeckel]

The header file declares several type definitions that guarantee a specified bit-size on all platforms supported by Qt for various basic types, for example qint8 which is a signed char guaranteed to be 8-bit on all platforms supported by Qt. The header file also declares the qlonglong type definition for long long int.

The header also provides series of macros that make it possible to print some Qt type aliases (qsizetype, qintptr, etc.) via a formatted output facility such as printf() or qDebug() without raising formatting warnings and without the need of a type cast.

Typedef for either qint32 or qint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, qintptr is a typedef for qint32; on a system with 64-bit pointers, qintptr is a typedef for qint64.

In order to print values of this type by using formatted-output facilities such as printf(), qDebug(), QString::asprintf() and so on, you can use the PRIdQINTPTR and PRIiQINTPTR macros as format specifiers. They will both print the value as a base 10 number.

Typedef for either qint32 or qint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, quintptr is a typedef for quint32; on a system with 64-bit pointers, quintptr is a typedef for quint64.

In order to print values of this type by using formatted-output facilities such as printf(), qDebug(), QString::asprintf() and so on, you can use the PRIdQPTRDIFF and PRIiQPTRDIFF macros as format specifiers. They will both print the value as a base 10 number.

In order to print values of this type by using formatted-output facilities such as printf(), qDebug(), QString::asprintf() and so on, you can use the PRIdQSIZETYPE and PRIiQSIZETYPE macros as format specifiers. They will both print the value as a base 10 number.

Typedef for either quint32 or quint64. This type is guaranteed to be the same size as a pointer on all platforms supported by Qt. On a system with 32-bit pointers, quintptr is a typedef for quint32; on a system with 64-bit pointers, quintptr is a typedef for quint64.

The type definitions are partly convenience definitions for basic types (some of which guarantee certain bit-sizes on all platforms supported by Qt), partly types related to Qt message handling. The functions are related to generating messages, Qt version handling and comparing and adjusting object values. And finally, some of the declared macros enable programmers to add compiler or platform specific code to their applications, while others are convenience macros for larger operations.

The header file declares several type definitions that guarantee a specified bit-size on all platforms supported by Qt for various basic types, for example qint8 which is a signed char guaranteed to be 8-bit on all platforms supported by Qt. The header file also declares the qlonglong type definition for long long int (__int64 on Windows).

Finally, the QtMsgType definition identifies the various messages that can be generated and sent to a Qt message handler; QtMessageHandler is a type definition for a pointer to a function with the signature void myMessageHandler(QtMsgType, const QMessageLogContext &, const char *). QMessageLogContext class contains the line, file, and function the message was logged at. This information is created by the QMessageLogger class.

The header file contains several functions comparing and adjusting an object's value. These functions take a template type as argument: You can retrieve the absolute value of an object using the qAbs() function, and you can bound a given object's value by given minimum and maximum values using the qBound() function. You can retrieve the minimum and maximum of two given objects using qMin() and qMax() respectively. All these functions return a corresponding template type; the template types can be replaced by any other type.

The remaining functions are qRound() and qRound64(), which both accept a double or float value as their argument returning the value rounded up to the nearest integer and 64-bit integer respectively, the qInstallMessageHandler() function which installs the given QtMessageHandler, and the qVersion() function which returns the version number of Qt at run-time as a string.

The header file provides a range of macros (Q_CC_*) that are defined if the application is compiled using the specified platforms. For example, the Q_CC_SUN macro is defined if the application is compiled using Forte Developer, or Sun Studio C++. The header file also declares a range of macros (Q_OS_*) that are defined for the specified platforms. For example, Q_OS_UNIX which is defined for the Unix-based systems.

The Q_INT64_C() and Q_UINT64_C() macros wrap signed and unsigned 64-bit integer literals in a platform-independent way. The Q_CHECK_PTR() macro prints a warning containing the source code's file name and line number, saying that the program ran out of memory, if the pointer is nullptr. The qPrintable() and qUtf8Printable() macros represent an easy way of printing text.

These functions return the value of the environment variable, varName, as a QString. If no variable varName is found in the environment and defaultValue is provided, defaultValue is returned. Otherwise QString() is returned.

Note: on Unix systems, this function may produce data loss if the original string contains arbitrary binary data that cannot be decoded by the locale codec. Use qgetenv() instead for that case. On Windows, this function is lossless.

It is important to note that qAsConst() does not copy its argument, it just performs a const_cast(t). This is also the reason why it is designed to fail for rvalues: The returned reference would go stale too soon. So while this works (but detaches the returned object):

Note: there's a limit on the length of the value, which is sufficient for all valid values of int, not counting leading zeroes or spaces. Values that are too long will either be truncated or this function will set ok to false.

For members of class type, we can use std::move(), as their move-constructor will do the right thing. But for scalar types such as raw pointers or integer type, move is the same as copy, which, particularly for pointers, is not what we expect. So, we cannot use std::move() for such types, but we can use std::exchange()/qExchange() to make sure the source object's member is already reset by the time we get to the initialization of our next data member, which might come in handy if the constructor exits with an exception.

This is perfectly safe, as the for-loop keeps the result of qExchange() alive for as long as the loop runs, saving the declaration of a temporary variable. Be aware, though, that qExchange() returns a non-const object, so Qt containers may detach.

This function provides an alternative way of doing approximated comparisons of floating-point numbers similar to qFuzzyCompare(). However, it returns the distance between two numbers, which gives the caller a possibility to choose the accepted error. Errors are relative, so for instance the distance between 1.0E-5 and 1.00001E-5 will give 110, while the distance between 1.0E36 and 1.00001E36 will give 127.

The return value can be considered as the "error", so if you for instance want to compare two 32-bit floating point numbers and all you need is an approximated 24-bit precision, you can use this function like this:

This function serves the same purpose as qFloatDistance(float, float), but returns the distance between two double numbers. Since the range is larger than for two float numbers ([-DBL_MAX,DBL_MAX]), the return type is quint64.

Note that comparing values where either p1 or p2 is 0.0 will not work, nor does comparing values where one of the values is NaN or infinity. If one of the values is always 0.0, use qFuzzyIsNull instead. If one of the values is likely to be 0.0, one solution is to add 1.0 to both values.

The message handler is a function that prints out debug messages, warnings, critical and fatal error messages. The Qt library (debug mode) contains hundreds of warning messages that are printed when internal errors (usually invalid function arguments) occur. Qt built in release mode also contains such warnings unless QT_NO_WARNING_OUTPUT and/or QT_NO_DEBUG_OUTPUT have been set during compilation. If you implement your own message handler, you get total control of these messages.

The pattern can also be changed at runtime by setting the QT_MESSAGE_PATTERN environment variable; if both qSetMessagePattern() is called and QT_MESSAGE_PATTERN is set, the environment variable takes precedence.

Note: The message pattern only applies to unstructured logging, such as the default stderr output. Structured logging such as systemd will record the message as is, along with as much structured information as can be captured.

Note: on desktop Windows, qgetenv() may produce data loss if the original string contains Unicode characters not representable in the ANSI encoding. Use qEnvironmentVariable() instead. On Unix systems, this function is lossless.

Warning: This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior.

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