C alternative tokens

C alternative tokens refer to a set of alternative spellings of common operators in the C programming language. They are implemented as a group of macro constants in the C standard library in the <iso646.h> header. The tokens were created by Bjarne Stroustrup for the pre-standard C++ language and were added to the C standard in a 1995 amendment to the C90 standard via library to avoid the breakage of existing code.

The alternative tokens allow programmers to use C language bitwise and logical operators which could otherwise be hard to type on some international and non-QWERTY keyboards. The name of the header file they are implemented in refers to the ISO/IEC 646 standard, a 7-bit character set with a number of regional variations, some of which have accented characters in place of the punctuation marks used by C operators.

The macros

The <iso646.h> header defines the following 11 macros as stated below:

Macro Defined as
and&&
and_eq&=
bitand&
bitor|
compl~
not!
not_eq!=
or||
or_eq|=
xor^
xor_eq^=

C++

The above-mentioned identifiers are operator keywords in the ISO C++ programming language and do not require the inclusion of a header file. For consistency, the C++98 standard provided both <iso646.h> and a corresponding <ciso646>. However they both had no effect, being empty. Some compilers, such as Microsoft Visual C++ have, at least in the past, required the header to be included in order to use these identifiers unless a compiler flag is set. The header <ciso646> was deprecated in C++17, and removed in C++20, while <iso646.h> was retained for compatibility with C.

See also

References

  1. ↑ "CppCon 2017: Panel "Grill the Committee"". YouTube. Archived from the original on 2021-12-12.
  2. ↑ "Rationale for International Standard - Programming Languages - C" (PDF). 5.10. April 2003. Archived (PDF) from the original on 2016-06-06. Retrieved 2010-10-17.
  3. ↑ Stroustrup, Bjarne (1994-03-29). Design and Evolution of C++ (1st ed.). Addison-Wesley Publishing Company. ISBN 0-201-54330-3.
  4. ↑ Lischner, Ray (2003). C++ in a Nutshell. O'Reilly Media. p. 384. ISBN 0-596-00298-X.
  5. ↑ Van Weert, Peter; Gregoire, Marc (2019). C++17 Standard Library Quick Reference. Apress. p. 277. ISBN 9781484249239.
  6. ↑ Deitel, Paul; Deitel, Harvey M. (2013). C++11 for Programmers. Pearson Education. p. 928. ISBN 9780133439878.
  7. ↑ "Logical AND Operator: &&". Microsoft Docs. 2021-11-23. Archived from the original on 2021-12-28. Retrieved 2021-12-27.
  8. ↑ Whitney, Tyler (2021-12-07). "<ciso646>". Microsoft Learn.
  9. ↑ Köppe, Thomas (2021-06-11). "Clarifying the status of the "C headers"". C++ Standards Committee Papers. ISO/IEC JTC1 SC22 WG21. Archived from the original on 2024-01-11.