Why is i an L-value while i is an R-value in C ?

Understanding the Difference in Value Category: i vs. i

In the realm of C programming, expressions like i and i may look similar but possess distinct value categories. The former, i, is considered an l-value, while the latter, i , falls under the r-value category.

Understanding L-values

L-values represent memory locations that can be both read from and written to. In other words, they denote variables or objects that can be assigned a value. When you increment i, you are requesting the compiler to first retrieve the current value of i, increment it by one, and then store the updated value back in the same memory location. Since i modifies the original variable, its result can be assigned to a variable or further manipulated. This makes i an l-value.

Contrast with R-values

R-values, on the other hand, represent constant values or expressions that can only be read from. They cannot be modified or assigned a new value. In the case of i , the operation returns a copy of the incremented value, leaving the original variable i unchanged. This means that i cannot be assigned to anything, as it does not represent a modifiable memory location. Therefore, i is categorized as an r-value.

Implications for Performance and Preference

Understanding the value category of these expressions is important for considering performance implications and coding preferences. Pre-increment ( i) is often preferred over post-increment (i ), especially when working with certain objects like iterators. This is because pre-increment directly modifies the original variable, eliminating the need for creating an extra copy.

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