Is it Safe to Call `delete` on a Stack-Allocated Variable in C ?

Can You Safely Call Delete on a Stack-Allocated Variable?

In the realm of C programming, it's crucial to understand the memory nuances associated with allocating variables on the stack or the heap. While programming style and design should be taken into account, it's essential to address a fundamental question: is it permissible to call delete on a variable allocated on the stack?

Examining the Issue

Consider the following code snippets:

int nAmount;
delete &nAmount;

class sample {
public:
    sample();
    ~sample() { delete &nAmount; }
    int nAmount;
};

The Safety Issue

The answer to the question is a resounding no. Calling delete on a stack-allocated variable is not safe and should be avoided.

Memory Allocation Principles

To understand why, it's important to grasp the principles of memory allocation. For every:

• malloc or calloc, there should be exactly one free.
• new, there should be exactly one delete.
• new[], there should be exactly one delete[].
• Stack allocation, there should be no explicit freeing or deletion (destructors are called automatically).

Illegal Mixing

Mixing these allocation methods is strictly forbidden. Attempting to free or delete[] an object allocated with new will result in undefined behavior. The same holds true for calling delete on a stack-allocated variable.

Consequences of Deletion

When calling delete on a stack-allocated variable, the compiler may perform optimization, such as elision, assuming the object is not used after it goes out of scope. However, explicitly calling delete on such a variable can lead to:

• Memory Corruption: Overwriting stack memory can corrupt other variables.
• Undefined Behavior: The compiler may optimize the code under the assumption that the object is not referenced after the scope ends. Calling delete can disrupt this behavior.
• Exception Handling Issues: Stack variables are automatically cleaned up during exception handling, but explicit deletion can interfere with this process.

Conclusion

To maintain memory integrity and avoid undefined behavior, it is essential to respect the memory allocation principles. Avoid calling delete on stack-allocated variables and adhere to the appropriate allocation and deallocation pairs: malloc/free, new/delete, and new[]/delete[].

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