Why Does C and C Allow Memberwise Array Assignment in Structs but Not for Standalone Arrays?

Why Memberwise Array Assignment within Structs is Supported in C and C

While memberwise assignment of arrays is generally prohibited in C and C , it is supported within structs. This apparent contradiction stems from the historical evolution of these languages.

In struct definitions, arrays were introduced as a convenient way to allocate contiguous memory for data. However, in C's early iterations, arrays were merely pointers to memory regions. Assigning one array to another thus resulted in a pointer assignment, not a element-wise copy.

This behavior persisted even when struct assignment was added in K&R C. Instead of defining a separate assignment operator for structs, the compiler simply used a memory copy operation (memcpy) to assign all members. This effectively included arrays within structs.

Consequently, struct assignment implicitly introduced a form of array assignment within the context of structs. However, this assignment remained restricted to within structs, and assigning an array directly to another array, even if it is contained in a struct, is still not supported in C and C .

This differentiation between arrays within structs and general arrays serves two purposes:

• Compatibility: It ensures backward compatibility with existing C code that relies on pointer arithmetic and array manipulation.
• Type Safety: Requiring explicit memory copying for general array assignments helps prevent errors and ensures type safety.

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