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Why is Dereferencing a Null Pointer Undefined Behavior in C ?

Patricia Arquette

Dec 13, 2024 am 06:37 AM

Why is Dereferencing a Null Pointer Undefined Behavior in C ?

The Undefined Behavior of Dereferencing a Null Pointer

In ISO C , dereferencing a null pointer is considered undefined behavior. This has raised questions about the reasons behind this decision.

Why Undefined Behavior?

The rationale for declaring dereferencing a null pointer as undefined behavior lies in the following factors:

1. Compiler Independence:
Dereferencing a null pointer would require the compiler to constantly check for it before each dereference on most CPU architectures. This overhead would significantly impact performance, especially for high-performance applications.

2. Machine Independence:
Dereferencing a null pointer would also depend on the underlying hardware architecture. The behavior could vary across different machines, leading to unpredictable results.

3. Addressing a Larger Issue:
Dereferencing a null pointer is only a symptom of a broader problem: the existence of invalid pointers. There are numerous ways to have an invalid pointer, and defining a consistent behavior for dereferencing any invalid pointer would be highly complex and inefficient.

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