Why Can\'t I Use `delete` on Memory Allocated with `malloc`?

Inconsistency in Memory Management: malloc vs delete

In C , memory management relies on a fundamental distinction between the functions malloc and new. While malloc is used for raw memory allocation, new is employed specifically for creating objects on the heap.

Unexpected Behavior with malloc and delete

However, an intriguing discrepancy arises when using malloc to allocate memory and then attempting to release it using delete. Surprisingly, in such cases, C compilers fail to generate errors or warnings.

Rationale for Undefined Behavior

This behavior is classified as undefined, stemming from the inability to verify the source of the allocated memory. Delete expects memory allocated by new, and malloc allocates raw memory without any object-related information. Thus, there's no reliable way to determine if the memory was allocated correctly.

Reversing the Process

Similar behavior occurs when allocating memory with new and releasing it with free. This reversal also results in undefined behavior.

Correct Practice: Smart Pointers

To avoid such inconsistencies, it's crucial to utilize smart pointers, which handle memory management automatically. By employing appropriate smart pointers (such as unique_ptr or shared_ptr), you can ensure that memory allocated with new is released with delete, and memory allocated with malloc is released with free.

Conclusion

Mixing memory management functions (malloc/new and free/delete) can lead to unpredictable behavior. To maintain consistency and minimize errors, it's essential to adhere to proper memory management practices by using smart pointers or adhering to the designated pairing of malloc/free and new/delete.

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