Why Do C Iterator Ranges Use a Half-Open Interval [begin, end)?

The Rationale Behind Standard Iterator Ranges Spanning [begin, end)

In the realm of C programming, iterator ranges have been intentionally defined to span [begin, end) rather than [begin, end]. This raises the question: why?

The primary reason hinges on the desire to simplify range size calculations. By establishing the end() function to point one past the actual end, it enables effortless determination of the range size as end() - begin(). This eliminates the need for additional computations or sentinel values, providing a consistent and intuitive approach across all range-based constructions.

Furthermore, the [begin, end) convention streamlines the iteration process. The classic for (it = begin; it != end; it) loop runs seamlessly end - begin times, offering a straightforward and readable iteration mechanism. In contrast, inclusive ranges would introduce off-by-one errors and convoluted code structures.

The choice to start counting at zero harmonizes with the half-open range convention. By assigning 0 as the "beginning" of a range with N elements, it enables the convenient representation of ranges as [0, N) without any adjustments or offsets.

In essence, the [begin, end) convention for standard iterator ranges stems from a desire for simplicity, consistency, and intuitive iteration. It allows for straightforward range size determination, effortless iteration control, and a natural starting point at zero.

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