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(C++) unsigned

unsigned is a keyword that modifies a data type to hold only positive values.

Examples

• unsigned example 1: one minus two

Advice

• Prefer plain char over signed char and unsigned char [8]
• Avoid using unsigned in a class interface; use int instead [1]
• Consider avoiding unsigned [2] or unsigned arithmetic [3] as using an unsigned instead of an int to gain one more bit to represent positive integers is almost never a good idea [4]
• If you do use unsigned, always check your ranges [6] (note that [6] is in favor of using unsigned)
• View signed to unsigned and unsigned to signed conversions with suspicion [5,7,9]

References

1. John Lakos. Large-Scale C++ Software Design. 1996. ISBN: 0-201-63362-0. Chapter 9.2.2: 'Avoid using unsigned in the interface; use int instead'
2. Joint Strike Fighter Air Vehicle C++ Coding Standards for the System Development and Demonstration Program. Document Number 2RDU00001 Rev C. December 2005. AV Rule 163: 'Unsigned arithmetic shall not be used.'
3. Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. ISBN: 0-201-88954-4. Chapter 4.10 'Advice', item 18: 'Avoid unsigned arithmetic'
4. Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. ISBN: 0-201-88954-4. Chapter 4.4 'Integer types': 'Using an unsigned instead of an int to gain one more bit to represent positive integers is almost never a good idea. Attempts to ensure that some values are positive by declaring variables unsigned will typically be defeated by implicit conversion rules'
5. Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. ISBN: 0-201-88954-4. Chapter 4.10 'Advice', item 19: 'View signed to unsigned and unsigned to signed conversions with suspicion'
6. C++ FAQ Lite. [29.12] What's the point of the L, U and f suffixes on numeric literals?: 'It's probably a good idea to use unsigned integers for variables that are always >= 0. [...] at least if you are careful to check your ranges'
7. C++ FAQ Lite. [29.12] What's the point of the L, U and f suffixes on numeric literals?: 'If you end up using unsigned variables, it is generally a good idea to force your numeric literals to also be unsigned'
8. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 6.6. Advice. page 169: '[9] Prefer plain char over signed char and unsigned char'
9. Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 6.6. Advice. page 169: '[10] Beware of conversions between signed and unsigned types'

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