Qt provides several ways to implement Inter-Process Communication (IPC) in Qt applications.

TCP/IP

The cross-platform QtNetwork module provides classes that make network programming portable and easy. It offers high-level classes (e.g., QNetworkAccessManager, QFtp) that communicate using specific application-level protocols, and lower-level classes (e.g., QTcpSocket, QTcpServer, QSslSocket) for implementing protocols.

Shared Memory

The cross-platform shared memory class, QSharedMemory, provides access to the operating system's shared memory implementation. It allows safe access to shared memory segments by multiple threads and processes. Additionally, QSystemSemaphore can be used to control access to resources shared by the system, as well as to communicate between processes.

D-Bus

The QtDBus module is a Unix-only library you can use to implement IPC using the D-Bus protocol. It extends Qt's Signals and Slots mechanism to the IPC level, allowing a signal emitted by one process to be connected to a slot in another process. This D-Bus page has detailed information on how to use the QtDBus module.

Qt COmmunications Protocol (QCOP)

The QCopChannel class implements a protocol for transferring messages between client processes across named channels. QCopChannel is only available in Qt for Embedded Linux. Like the QtDBus module, QCOP extends Qt's Signals and Slots mechanism to the IPC level, allowing a signal emitted by one process to be connected to a slot in another process, but unlike QtDBus, QCOP does not depend on a third party library.