Why Does Memberwise Array Assignment Work in C and C Structures But Not for Arrays Generally?

Understanding Array Assignments in C and C : Memberwise vs General

In C and C , assigning arrays directly is not supported. However, one notable exception is the memberwise assignment of arrays within structures. This raises the question: why does this exception exist?

Historical Background and Language Evolution

The evolution of arrays in C provides context for understanding this behavior. Initially, in languages like B and BCPL, arrays were essentially pointers, not distinct data types. This presented challenges when incorporating arrays into structure definitions in C.

To address this, the compiler was modified to implicitly handle arrays in structures. Arrays were tracked internally without requiring explicit pointers. This allowed for the seamless integration of arrays into structures without runtime memory allocation.

However, the original pointer-based concept still influenced the treatment of arrays in C. The "arrays convert to pointer" concept, where accessing an array index effectively references a pointer, remained in place for compatibility reasons.

Memberwise Assignment Exception

Despite the general prohibition on array assignment, memberwise assignment within structures emerged as a special case. Struct assignment, introduced in a later revision of C, was defined as a memcpy operation that copied the raw memory of the struct.

As arrays are stored contiguously within structures, this memcpy operation effectively performed an element-wise copy of the array. Thus, by assigning one structure to another, the arrays within them were also implicitly copied.

Philosophical Perspective

In a broader sense, the support for memberwise array assignment in structs is a reflection of the flexibility and adaptability of C and C . The language allows for extending data types with user-defined structures and complex constructs.

While general array assignment would require explicit syntax, using the struct-assignment mechanism for arrays inside structures provides a consistent and intuitive approach that doesn't introduce unnecessary syntax or implementation complexity.

The above is the detailed content of Why Does Memberwise Array Assignment Work in C and C Structures But Not for Arrays Generally?. For more information, please follow other related articles on the PHP Chinese website!