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

Why String Literals Differ from Other Literals in L-Value Status

C and C languages distinguish between string literals and other literals when it comes to their L-value status. Understanding the rationale behind this distinction requires delving into the differences between string literals and other literals from an object-oriented perspective.

String Literals as Objects

While all literals represent fixed values, including numbers, characters, and boolean values, string literals stand out as objects. Objects reside in memory and have an address, making them accessible for modification. Other literals, on the other hand, are stored in registers or constants and cannot be modified.

L-Values and Objects

In C and C , an L-value refers to a variable that can be assigned a value (i.e., a left-value). Since objects are the only entities that can be assigned values and modified, it makes sense that string literals, being objects, qualify as L-values.

Historical Reasons

The array type is used to represent string literals in C and C . Arrays in C cannot exist in expressions as anything other than L-values. To use a string literal as an L-value, it was given an array type rather than a pointer type. This approach, however, makes string literals less versatile, as they cannot be used with the sizeof operator.

Modern Developments

With the introduction of compound literals in C99, the concept of non-object literals being L-values extended to other constructs, making the unique L-value status of string literals less exceptional.

Hardware Implications

The distinction between L-value and R-value is theoretically related to hardware architecture. L-values refer to memory locations, while R-values represent values that are stored in registers or dedicated hardware components, such as the stack or constant storage. However, modern compilers optimize code to blur this distinction somewhat, allowing R-values to be stored in memory if beneficial for performance.

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