Why Can a `char*` Alias a `struct*` in C/C But Not Vice Versa?

Char* Aliasing: A Pointer's Versatility

The strict aliasing rule governs the ability for pointers to implicitly alias with each other. It allows a char pointer to alias objects of arbitrary types, while restricting the converse. This asymmetry sparks curiosity: how can a char alias a struct* pointing to the same location, yet not vice versa?

For a char and struct referencing the same memory address, both can indeed alias each other. However, the distinction lies in their usage:

• Char Aliasing Permission: You can freely use a char to access the individual bytes of a struct, as it ignores the strict aliasing rule. This allows you to efficiently read and manipulate data at a low level.
• Struct Aliasing Restriction: Conversely, using a struct to access bytes directly via a char* alias is prohibited by the alias rule. While the two pointers share the same address, they represent different types. Attempting to reinterpret the bytes as a struct could result in undefined behavior.

This asymmetry ensures that type safety is maintained, preventing unintended data corruption. Char* pointers provide convenience for byte-level manipulations without compromising the integrity of structured data.

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