- Qt 5.15
- Qt Core
- Qt 5.15.15 Reference Documentation

# Qt Core

## Core Functionalities

Qt Core 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 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 components in the `Qt5` package:

     find_package(Qt5 COMPONENTS Core REQUIRED)
     target_link_libraries(mytarget Qt5::Core)

See also the Build with CMake overview.

### Building with qmake

If you use qmake to build your projects, Qt5Core 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 Thread Support 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
- The State Machine Framework
- How to Create Qt Plugins
- The Event System

## Licenses and Attributions

Qt Core is available under commercial licenses from The Qt Company. In addition, it is available under free software licenses. Since Qt 5.4, these free software licenses are 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 qtmain Library. This library is available under commercial licenses and also under the BSD 3-clause "New" or "Revised" License.

Furthermore, Qt Core in Qt 5.15.15 may contain third party modules under following permissive licenses:

Data Compression Library (zlib), version 1.2.13 | 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 3.1.5 | BSD 3-clause "New" or "Revised" License
FreeBSD strtoll and strtoull, version 18b29f3fb8abee5d57ed8f4a44f806bec7e0eeff | BSD 3-clause "New" or "Revised" License
MD4 | Public Domain
MD5 | Public Domain
PCRE2 - Stack-less Just-In-Time Compiler, version 10.42 | BSD 2-clause "Simplified" License
PCRE2, version 10.42 | BSD 3-clause "New" or "Revised" License
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 https://github.com/BrianGladman/sha/ commit 4b9e13ead2c5b5e41ca27c65de4dd69ae0bac228 | BSD 2-clause "Simplified" License
Secure Hash Algorithms SHA-384 and SHA-512 | BSD 3-clause "New" or "Revised" License
Text Codec: EUC-JP | BSD 2-clause "Simplified" License
Text Codec: EUC-KR | BSD 2-clause "Simplified" License
Text Codec: GBK | BSD 2-clause "Simplified" License
Text Codec: ISO 2022-JP (JIS) | BSD 2-clause "Simplified" License
Text Codec: Shift-JIS | BSD 2-clause "Simplified" License
Text Codec: TSCII | BSD 2-clause "Simplified" License
Text Codecs: Big5, Big5-HKSCS | BSD 2-clause "Simplified" License
The Public Suffix List, version 4e6c53ca9c667b74a7d332d1512d2c362af91516, fetched on 2023-07-31 | Mozilla Public License 2.0
TinyCBOR, version 0.6+patches | MIT License
Unicode Character Database (UCD), version 26 | Unicode License Agreement - Data Files and Software (2016)
Unicode Common Locale Data Repository (CLDR), version v39 | Unicode License Agreement - Data Files and Software (2016)
forkfd | MIT License

## Reference

These are links to the API reference materials.

- C++ Classes
  - Animation Classes
  - Threading Classes
  - Container Classes
  - Plugin Classes
  - Implicitly Shared Classes
  - State Machine Classes
  - Input/Output Classes
  - Event Classes