Why is `size_t` Unsigned Despite the Risks of Implicit Conversions?

Why is size_t Unsigned?

Question:

Stroustrup's writings emphasize the undesirability of using unsigned integers to represent positive values due to potential implicit conversion issues. However, size_t is unsigned, seemingly contradicting this advice. Should we minimize its use in favor of other types?

Answer:

size_t is unsigned due to historical reasons. On 16-bit systems, limiting strings to 32 KB would be impractical, necessitating a wider data type for indices.

Modern Considerations:

However, this reasoning is less applicable in modern 32-bit and 64-bit architectures. More importantly, the implicit conversion rules in C and C make unsigned types susceptible to bugs, especially when used for numerical operations and comparisons.

Recommendation:

In modern programming, it is generally preferable to use signed types such as ptrdiff_t for indices and counters, even if negative values are not expected. This avoids the potential pitfalls of unsigned types and aligns with the recommendations of experienced programmers like Scott Meyers.

Historical Note:

The decision to make size_t unsigned was not a mistake but rather a practical choice based on the technical limitations of the time. However, with the advent of more powerful architectures, signed types are generally more appropriate in most modern programming contexts.

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