Should You Null Pointers in C Destructors?

Is NULLing Pointers in Destructors Worthwhile?

In C , when managing memory with raw pointers, it's essential to handle object destruction properly. One common practice is to set pointers to NULL in destructors to "clean up" allocated memory. However, the question arises: is this practice really necessary?

In the destructor of a class that allocates memory, such as:

<code class="cpp">class Foo {
  Foo() : bar(new Bar) {}
  ~Foo() { delete bar; }
  void doSomething() { bar->doSomething(); }
private:
  Bar* bar;
};</code>

Setting the pointer bar to NULL within the destructor is considered ineffective time-wise, assuming that the memory is correctly deallocated. However, this practice has sparked discussions about potential benefits, particularly in debugging scenarios.

Some argue that setting pointers to NULL in debug builds can aid in debugging. However, this approach is discouraged because it can potentially hide errors in debugging builds. By avoiding NULL checks, a dangling reference to a deleted object may still be used in the debug build, leading to unpredictable behavior.

If the intention is to "clear" the pointer, a better approach is to set it to a known invalid or diagnostic value. This technique allows for easier detection and diagnostic ability. For instance, instead of setting bar to NULL, it could be set to a known bad pointer value. In this way, any attempts to use the pointer will result in a crash, making it easier to locate and fix the potential issue.

When working with raw pointers, it's important to remember the following rule: avoid setting pointers to NULL in destructors. This practice is generally not beneficial and may even lead to hidden bugs in debugging builds. It's recommended to rely on the proper memory management practices and avoid relying on this specific technique.

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