Why Does C Throw Error C2106 When Assigning Arrays?

Array Assignment Conundrum: Understanding the Error C2106

In C , attempting to assign one array to another can trigger the infamous error C2106. This enigmatic message perplexes many programmers, leaving them wondering why such a straightforward operation is prohibited. Let's delve deeper into the underlying rationale behind this restriction.

Contrary to intuitive expectations, arrays in C are not assignable. Unlike scalar variables, which can be freely assigned new values, arrays do not possess this capability due to their inherent nature as fixed-size aggregates. The reason lies in the intricate implementation details of arrays in C . In simplest terms, an array's memory allocation is fundamentally different from that of scalar variables, making direct assignment technically infeasible.

As a consequence of this limitation, attempting to assign one array to another, such as in the example provided, triggers the error C2106. The compiler detects the improper assignment and signals that the left operand, in this case, the array values, must be an l-value, meaning a variable that can be modified. Arrays, however, are inherently not modifiable in this way, hence the error.

If the requirement persists to emulate array assignment functionality, programmers have alternative options at their disposal. One approach involves utilizing modern C features, namely the std::array class or the std::vector container. These offer the desired array-like behavior while adhering to the rules of object-oriented programming, allowing for straightforward value assignment.

Alternatively, for those constrained to using legacy C-style arrays, copying elements via a loop or employing functions such as std::copy provides a viable solution. By manually copying each array element, the effect of assigning one array to another can be achieved indirectly.

It's worth noting an additional nuance regarding array initialization. In the example, the values array is initialized with an empty curly brace list {}. This shorthand syntax relies on the C standard, which dictates that unspecified aggregate elements are value initialized. In the case of integers, this equates to initialization of all unspecified elements to zero. Hence, both the explicit array initialization approach and the empty initializer list technique result in identical outcomes.

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