Why is i an l-value, but i is not?

L-Values in Expressions: The Case of Increment Operators i vs. i

The concept of l-values is central to understanding C expressions. An l-value refers to a memory location that stores a value. i and i are both increment operators, but they have a subtle difference in their nature as l-values.

Why is i an l-value?

i is considered an l-value because it refers to the incremented value of i. The pre-increment operator first increments the variable i and then returns its reference. This means that the result of i is the modified variable i itself, which can be stored in a new location or used as a reference to its value.

Why is i not an l-value?

In contrast, i is not an l-value because it refers to a temporary copy of the incremented value. The post-increment operator first creates a temporary copy of the current value of i, increments it, and then discards the copy. The result of i is a temporary variable that cannot be assigned to or referenced directly.

Practical Implications

Understanding the l-value nature of i and i has practical implications in C programming:

• Assignment: i can be used in assignment statements, such as i = 5, while i cannot.
• Iterator Incrementation: Pre-incrementing iterators (e.g., it in STL) is preferred for performance reasons because it directly manipulates the iterator object, avoiding the temporary copies created by post-incrementing.

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