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[1] and were added to the C standard in a 1995 amendment to the C90 standard via library to avoid the breakage of existing code.

C standard library (libc)
General topics
Miscellaneous headers

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:[2]

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.[3] For consistency, the C++98 standard provides the header <ciso646>. However the latter file has no effect, being empty.[4] 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.[5]

See also

References
  1. "CppCon 2017: Panel "Grill the Committee"". 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. 212. ISBN 0-596-00298-X.
  5. "Logical AND Operator: &&". Microsoft Docs. 2021-11-23. Archived from the original on 2021-12-28. Retrieved 2021-12-27.
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