C alternative tokens
| C standard library (libc) |
|---|
| General topics |
| Miscellaneous headers |
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[edit]
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++[edit]
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 provided both <iso646.h> and a corresponding <ciso646>. However they both had no effect, being empty.[4][5] 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.[6][7] The header <ciso646> was deprecated in C++17, and removed in C++20,[8] while <iso646.h> was retained for compatibility with C.[9]
See also[edit]
References[edit]
- ^ "CppCon 2017: Panel "Grill the Committee"". YouTube. Archived from the original on 2021-12-12.
- ^ "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.
- ^ Stroustrup, Bjarne (1994-03-29). Design and Evolution of C++ (1st ed.). Addison-Wesley Publishing Company. ISBN 0-201-54330-3.
- ^ Lischner, Ray (2003). C++ in a Nutshell. O'Reilly Media. p. 384. ISBN 0-596-00298-X.
- ^ Van Weert, Peter; Gregoire, Marc (2019). C++17 Standard Library Quick Reference. Apress. p. 277. ISBN 9781484249239.
- ^ Deitel, Paul; Deitel, Harvey M. (2013). C++11 for Programmers. Pearson Education. p. 928. ISBN 9780133439878.
- ^ "Logical AND Operator:
&&". Microsoft Docs. 2021-11-23. Archived from the original on 2021-12-28. Retrieved 2021-12-27. - ^ Whitney, Tyler (2021-12-07). "<ciso646>". Microsoft Learn.
- ^ 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.
External links[edit]
- : alternative spellings – Base Definitions Reference, The Single UNIX Specification, Version 4 from The Open Group