What Happens to Pointers Referencing the Same Object After One is Deleted in C ?

Pointers to Released Memory in C

After deleting a pointer, confusion arises regarding the validity of other pointers referencing the same object. This article aims to clarify this behavior in C .

Consider the following code:

<code class="cpp">A* a = new A();
A* b = a;

delete a;

A* c = a; // Illegal (C++11)
A* d = b; // Debatable legality

// Points to deallocated memory, Undefined in C++11
A* aAddr = &a;</code>

C 11 Behavior:

• Assigning to c from the previously deleted pointer a causes undefined behavior since a is now an invalid pointer value.
• However, d points to a copy of a made before the deletion. Although reading the value of b points to a deallocated memory location, this action is implementation-defined.

C 14 Behavior:

• Assigning to both c and d from the invalid pointer a still causes undefined behavior.
• Copying the value of an invalid pointer, as done here with b, is also implementation-defined behavior.

According to the C 11 standard, using an invalid pointer value (including copying it) causes undefined behavior. In C 14, such operations have implementation-defined behavior, meaning the behavior may vary across different compilers and operating systems.

Therefore, in both C 11 and C 14, it is critical to avoid using pointers that have been deleted or refer to deallocated memory. Doing so can lead to unpredictable and potentially erroneous behavior.

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