What is the difference between multi-threading and multi-processing in C++?

The difference between C++ multi-threading and multi-processing is:

1. Execution method: Multithreading involves creating multiple threads to execute concurrently within the same process, while multiprocessing involves creating multiple independent processes to execute concurrently within the operating system.
2. Memory and resources: In a multi-threading environment, threads share the same memory and resources within a process, allowing multiple threads to access the same memory area directly. In contrast, in a multi-processing environment, each process has its own independent memory space, requiring the use of specific mechanisms for inter-process communication.
3. Switching cost: The cost of switching between threads is relatively low, as it only requires saving and restoring a small amount of register states. On the other hand, the cost of switching between processes is higher, as it requires switching the entire context environment of the process.
4. Synchronization and communication: Sharing resources in the same process makes synchronization and communication among multiple threads more convenient. Mechanisms like shared memory, semaphores, and mutex locks can be used for synchronization and communication between threads. In contrast, additional mechanisms such as pipes, message queues, and shared files are needed for communication and synchronization between multiple processes.
5. Safety: When multiple threads share the same process resources, appropriate synchronization control is required to avoid issues such as data race and deadlock. On the other hand, each process in a multi-process setup has its own independent memory space, which makes it relatively safer.
6. Debugging and maintenance: Multithreading is relatively complex during debugging and maintenance because multiple threads share the resources of the same process, requiring attention to thread competition and synchronization issues; multiprocessing is relatively independent, making debugging and maintenance relatively simple.

In conclusion, multithreading is suitable for concurrent processing and sharing data/resources within the same process, while multiprocessing is suitable for independent, isolated concurrent processing.