Why Are String Literals L-Values in C and C ?

The Anomaly of String Literals as L-Values

In programming, literals represent constant values that cannot be modified. However, in C and C , string literals stand out as an exception to this rule. While all other literals are r-values (temporaries), string literals possess the peculiar trait of being l-values.

Rationale for String Literals as L-Values

This unique behavior stems from the intrinsic nature of string literals. Unlike basic data type literals (e.g., integers, floating-point numbers), string literals resemble objects. In C, arrays are the closest construct to objects, and string literals are fundamentally arrays of characters.

Significance of L-Values

L-values indicate objects that can be assigned to and reside at an identifiable memory location. In the case of arrays, being l-values allows direct manipulation of individual elements. Conversely, r-values cannot be assigned to directly and represent temporary values.

Memory Model Considerations

The distinction between l-values and r-values is rooted in computer architecture. Early computers utilized separate memory regions for modification (writeable) and fetching (readonly). L-values represented modifiable data, while r-values served as immutable references.

Alternative Design Consideration

String literals could have been designed with pointer types, resembling constant pointers to string "contents." However, such an approach would have diminished their usefulness. For instance, the sizeof operator would have been inapplicable to them.

Evolution in C99

The C99 standard introduced compound literals, granting l-value status to other literals. This change further underscores that l-values are no longer limited to string literals alone but are becoming the norm.

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