- Qt 6.9
- Qt Core
- Qt 6.9.3 Reference Documentation

# Qt Core

The Qt Core module adds these features to C++:

- a very powerful mechanism for seamless object communication called signals and slots
- queryable and designable object properties
- hierarchical and queryable object trees that organize object ownership in a natural way with guarded pointers (QPointer)
- a dynamic cast that works across library boundaries

The following pages provide more information about Qt's core features:

- The Meta-Object System
- The Property System
- Object Model
- Object Trees & Ownership
- Signals & Slots

## Using the Module

Using a Qt module's C++ API requires linking against the module library, either directly or through other dependencies. Several build tools have dedicated support for this, including CMake and qmake.

### Building with CMake

Use the `find_package()` command to locate the needed module component in the `Qt6` package:

     find_package(Qt6 REQUIRED COMPONENTS Core)
     target_link_libraries(mytarget PRIVATE Qt6::Core)

For more details, see the Build with CMake overview.

### Building with qmake

If you use qmake to build your projects, Qt Core is linked by default.

## Threading and Concurrent Programming

Qt provides thread support in the form of platform-independent threading classes, a thread-safe way of posting events, and signal-slot connections across threads. Multithreaded programming is also a useful paradigm for performing time-consuming operations without freezing the user interface of an application.

The Multi-threading in Qt page contains information on implementing threads in applications. Additional concurrent classes are provided by the Qt Concurrent module.

## Input/Output, Resources, and Containers

Qt provides a resource system for organizing application files and assets, a set of containers, and classes for receiving input and printing output.

- Container Classes
- Serializing Qt Data Types
- Implicit Sharing

In addition, Qt Core provides a platform-independent mechanism for storing binary files in the application's executable.

- The Qt Resource System

## Additional Frameworks

Qt Core also provides some of Qt's key frameworks.

- The Animation Framework
- JSON Support in Qt
- CBOR Support in Qt
- Inter-Process Communication
- How to Create Qt Plugins
- The Event System
- Application Permissions

## Reference

- C++ Classes
  - Animation Classes
  - Threading Classes
  - Container Classes
  - Plugin Classes
  - Implicitly Shared Classes
  - Input/Output Classes
  - Event Classes
- CMake API
  - CMake Commands
  - CMake Variables
  - CMake Target Properties

## Module Evolution

Changes to Qt Core lists important changes in the module API and functionality that were made for the Qt 6 series of Qt.

## Licenses and Attributions

Qt Core is available under commercial licenses from The Qt Company. In addition, it is available under free software licenses: The GNU Lesser General Public License, version 3, or the GNU General Public License, version 2. See Qt Licensing for further details.

Executables on Windows potentially link against The QtEntryPoint Library. This library is available under commercial licenses and also under the BSD 3-clause "New" or "Revised" License.

Furthermore, Qt Core in Qt 6.9.3 may contain third party modules under the following permissive licenses:

Apache Tika MimeType Definitions, version 5101bc7fb090ed7deffe56837d7633c9485a1e5d | Apache License 2.0
BLAKE2 (reference implementation), version ed1974ea83433eba7b2d95c5dcd9ac33cb847913 | Creative Commons Zero v1.0 Universal or Apache License 2.0
Data Compression Library (zlib), version 1.3.1 | zlib License
Easing Equations by Robert Penner | BSD 3-clause "New" or "Revised" License
Efficient Binary-Decimal and Decimal-Binary Conversion Routines for IEEE Doubles, version 3.3.1 | BSD 3-clause "New" or "Revised" License
MD4 | Public Domain
MD5 | Public Domain
PCRE2 - Stack-less Just-In-Time Compiler, version 10.46 | BSD 2-clause "Simplified" License
PCRE2, version 10.46 | BSD 3-clause "New" or "Revised" License with PCRE2 binary-like Packages Exception
QEventDispatcher on macOS | BSD 3-clause "New" or "Revised" License
Secure Hash Algorithm SHA-1 | Public Domain
Secure Hash Algorithm SHA-3 - Keccak, version 3.2 | Creative Commons Zero v1.0 Universal
Secure Hash Algorithm SHA-3 - brg_endian, version 4b9e13ead2c5b5e41ca27c65de4dd69ae0bac228 | BSD 2-clause "Simplified" License
Secure Hash Algorithms SHA-384 and SHA-512 | BSD 3-clause "New" or "Revised" License
SipHash Algorithm | Creative Commons Zero v1.0 Universal
TinyCBOR, version 0.6.1 | MIT License
Unicode Character Database (UCD), version 34 | Unicode License Agreement - Data Files and Software (2016)
Unicode Common Locale Data Repository (CLDR), version v47 | Unicode License v3
forkfd | MIT License