Why is Dereferencing an Uninitialized Pointer Undefined Behavior in C ?

Dereferencing Uninitialized Pointers: A Journey into Undefined Behavior

Defining dereferencing an uninitialized pointer as undefined behavior in the C standard requires a comprehensive understanding of the language's semantics. While the identification of undefined behavior (UB) is not readily apparent in the cited sections of the standard, a deeper exploration reveals the underlying rationale.

Section 4.1 of the C standard defines the conversion of an lvalue (such as a pointer) to an rvalue (an expression that can be evaluated to a value). This conversion is allowed for non-function, non-array types, provided that the lvalue refers to an initialized object of the specified type or its derived type. However, if the lvalue references an uninitialized or invalid object, the conversion results in undefined behavior.

In the provided code snippet:

int* ptr;
*ptr = 0;

The pointer ptr is declared but not initialized, making it an uninitialized object. The subsequent attempt to dereference this pointer (*ptr) constitutes an lvalue-to-rvalue conversion, violating the condition specified in Section 4.1. Since the conversion involves an uninitialized object, the behavior is deemed undefined.

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