Why Are String Literals L-Values in C and C While Other Literals Are R-Values?

Why String Literals Are L-Values While Other Literals Are R-Values

In C and C , string literals are an exception to the rule that all literals are r-values. The C 03 standard states that, while other literals are r-values, string literals are l-values. Similarly, the C99 standard defines string literals as l-values.

Rationale

This distinction stems from the nature of string literals as objects. Unlike other literals, which represent fixed values, string literals are objects of array type. In C, arrays are only allowed to exist as l-values in expressions.

To make string literals more useful, it would be impractical to define them as having pointer type instead of array type. This would prevent the application of the sizeof operator on string literals.

The Case of Compound Literals

The C99 standard introduced compound literals, which are also l-values. Their introduction suggests a shift towards the norm of literals being l-values rather than a special exception. Compound literals allow the creation of temporary objects initialized with a specific value. Like string literals, they exist as l-values.

Historical Context

The reason for this distinction may also be rooted in hardware architecture. In early computers, strings were stored as character arrays rather than pointers to character arrays. This historical context may have influenced the choice of defining string literals as l-values.

Conclusion

String literals are defined as l-values in C and C because they are objects of array type. While other literals are fixed values, string literals are objects that can be modified or referenced. This distinction allows for more flexible use of string literals in programming.

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