When writing robust C++ programs, you must consider how your code behaves when exceptions are thrown. Exception safety refers to the guarantees your code provides about program state and resource management in the presence of exceptions. There are three widely recognized levels of exception safety:

1. Basic Guarantee: your code ensures that even if an exception is thrown, program invariants are preserved and no resources leak, but the state of affected objects may be valid but unspecified;
2. Strong Guarantee: your code provides transactional behavior: if an operation fails due to an exception, the program state is unchanged, as if the operation was never attempted;
3. No-throw Guarantee: your code guarantees that no exceptions will be thrown under any circumstances.

These guarantees matter because they help you reason about program correctness and resource cleanup, especially in complex systems where exceptions might be thrown at many points.

One of the most effective ways to achieve exception safety is through the RAII idiom—Resource Acquisition Is Initialization. With RAII, you tie the lifetime of a resource (such as memory, file handles, or network sockets) to the lifetime of a C++ object. When the object is constructed, it acquires the resource, and when the object goes out of scope, its destructor automatically releases the resource. This approach ensures that resources are properly cleaned up even if an exception is thrown, because destructors are always called for objects with automatic storage duration.

Key points:

• RAII binds resource management to object lifetime;
• Constructors acquire resources, while destructors release them;
• Destructors are always called, ensuring cleanup even during stack unwinding after exceptions;
• This pattern prevents resource leaks and simplifies exception-safe code.