C alternative tokens

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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.

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[]

  • Digraphs and trigraphs in C

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. Retrieved 2021-12-27.{{cite web}}: CS1 maint: url-status (link)

External links[]

  • iso646.h: alternative spellings – Base Definitions Reference, The Single UNIX Specification, Issue 7 from The Open Group
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