Should Exceptions Be Thrown from Constructors in C ?

Throwing Exceptions from Constructors: A Detailed Discussion

When dealing with object initialization in C , the question of utilizing exceptions within constructors arises. To provide a thorough examination of this topic, we'll delve into a real-world scenario involving the use of a mutex wrapper class.

Problem:

In an attempt to provide a secure interface around a POSIX mutex, a programmer designs the following class:

class Mutex {
public:
  Mutex() {
    if (pthread_mutex_init(&mutex_, 0) != 0) {
      throw MutexInitException();
    }
  }
  ...
};

Question:

Is this design approach appropriate, considering the implications of throwing exceptions from constructors?

Answer:

The answer is a resounding yes. Throwing an exception from a constructor that encounters failures is considered a standard practice in object-oriented programming. According to the "Exceptional C FAQs," if a class "cannot enter a valid state during construction, the constructor should throw an exception."

Using exceptions in this context ensures that an invalid object is not created, mitigating the risks associated with relying on a faulty mutex.

Alternative Approach:

An alternative solution, which is less preferred but still viable, would be to create an init() member function within the Mutex class, which would then perform the necessary initialization. This approach introduces the caveat that every client code using the mutex must explicitly call init() before using the object.

Benefits of Throwing Exceptions from Constructors:

The primary advantage of throwing exceptions from constructors is that it enforces safety by preventing the creation of invalid objects during initialization. It also aligns with the RAII (Resource Acquisition Is Initialization) principle, which proponents argue aligns well with exception-based programming.

Conclusion:

While opinionated debates may exist regarding the usage of exceptions in constructors, the consensus among experts is clear: throwing exceptions from constructors is an acceptable approach when ensuring the integrity and validity of an object during initialization.

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