Question

Until this chapter, we have found that dealing with errors detected by constructors can be awkward. Exception handling gives us a better means of handling such errors. Consider a constructor for a string class. The constructor uses new to obtain space from the free store. Suppose new fails. Show how you would deal with this without exception handing. Discuss the key issues. Show how you would deal with such memory exhaustion with exception handling. Explain why the exception-handling approach is superior.

Short answer

Exception handling is better as it separates error handling from main code, enhancing readability and maintainability.

Step-by-step solution

Understanding the Problem of Memory Allocation

Constructors may fail if they use `new` to allocate memory dynamically and the memory request cannot be fulfilled. If `new` fails to allocate the requested memory, it returns a null pointer or throws a `std::bad_alloc` exception, depending on the environment.

Dealing with Memory Allocation Failure Without Exception Handling

If we don't use exception handling, we must manually check the pointer returned by `new`. For example, in C++, you can allocate memory and immediately check whether the pointer is `nullptr`. If it is `nullptr`, the constructor should appropriately handle the error, perhaps by returning an error code or setting some error flag.

Implementing Memory Check Without Exception

Here is a C++ example for a string class constructor without exception handling: ```cpp class String { char* data; public: String(const char* init) { data = new char[strlen(init) + 1]; if (data == nullptr) { // check for allocation failure // handle error: log, cleanup, etc. } else { strcpy(data, init); } } // other members }; ```

Handling Memory Allocation with Exception Handling

In modern C++, `new` automatically throws a `std::bad_alloc` exception if the memory can't be allocated. You can surround the allocation with a `try-catch` block to handle this: ```cpp class String { char* data; public: String(const char* init) { try { data = new char[strlen(init) + 1]; strcpy(data, init); } catch (const std::bad_alloc& e) { // handle exception: log, throw further, etc. } } // other members }; ```

Justifying Why Exception Handling is Superior

Exception handling is superior because it provides a clear separation between error-handling code and normal program logic. It eliminates the need to constantly check for errors, making the code cleaner and more maintainable. It also provides a unified way of handling all types of errors, not just those related to memory allocation.

Key concepts

Constructors in C++

In C++, a constructor is a special function that is automatically invoked when an object of a class is created. Constructors are responsible for initializing the objects of the class. They play a vital role in setting up an object's initial state by assigning values to its data members.

One key aspect of constructors in C++ is their ability to allocate memory dynamically using the `new` operator. For example, if we have a class `String` that manages a character array, its constructor might use `new` to allocate memory for the array. This allocation is crucial because the success of the constructor often depends on the availability of memory.

• Constructors can have parameters to customize object initialization.
• They do not have return types, not even `void`.
• If a constructor fails, it should handle the failure gracefully, often by using exception handling strategies.

Constructors are fundamental in C++, especially in managing class resources efficiently and ensuring that objects are always in a valid state. Efficient constructors enhance program stability and performance.

Memory Allocation

Memory allocation in C++ refers to the process of reserving computer memory to store data. This process can be dynamic, where memory is allocated during program execution using the `new` operator. Dynamic memory allocation is essential for handling variable data sizes at runtime.

C++ offers two main types of memory allocation:

• Static Memory Allocation: Memory size is determined at compile-time and remains fixed throughout the execution.
• Dynamic Memory Allocation: Allocated at runtime, making it flexible for applications where data size can vary significantly.

When using `new` for dynamic memory allocation, the program requests memory from the heap (or free store). If the allocation is successful, `new` returns a pointer to the allocated memory. However, if the system runs out of memory, `new` behavior varies based on the environment: it may return `nullptr` or throw a `std::bad_alloc` exception.

Proper memory allocation and deallocation are critical in C++ to prevent memory leaks and ensure efficient use of resources. It's crucial to pair every `new` with a `delete` to free the allocated memory when it's no longer needed.

Error Handling Strategies

Error handling strategies in C++ help programs manage and respond to errors that arise during execution. This is particularly important in cases of resource failures, such as memory allocation errors.

Two principal approaches to error handling in C++ include:

• Manual Error Checking: This traditional method involves checking return values or flags to detect errors. For instance, after attempting a memory allocation, the code might check if the returned pointer is `nullptr` and handle the error accordingly. This method can clutter code with checks and make it difficult to maintain.
• Exception Handling: A modern approach that separates error-handling code from the main logic. Exceptions in C++ are used with `throw`, `try`, and `catch` blocks. When an error occurs, such as memory exhaustion, an exception is thrown, and the program can catch this using a `catch` block. This way, error details can be logged or operations can be safely terminated without burying the main logic with error checks.

Exception handling is often preferred due to its ability to simplify code and facilitate more robust error management. It ensures that the program can gracefully recover from errors, providing a user-friendly experience.