Alternative operator representations
C++ (and C) source code may be written in any non-ASCII 7-bit character set that includes the ISO 646:1983 invariant character set. However, several C++ operators and punctuators require characters that are outside of the ISO 646 codeset: {, }, [, ], #, \, ^, |, ~
. To be able to use character encodings where some or all of these symbols do not exist (such as the German DIN 66003), C++ defines two kinds of alternatives: additional keywords that correspond to the operators that use these characters and special combinations of two or three ISO 646 compatible characters that are interpreted as if they were a single non-ISO 646 character.
Contents |
[edit] Alternative tokens
There are alternative spellings for several operators defined as tokens with special meaning in the C++ standard.
Primary | Alternative |
---|---|
&&
|
and
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&=
|
and_eq
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&
|
bitand
|
|
|
bitor
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~
|
compl
|
!
|
not
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!=
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not_eq
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|| | or |
|=
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or_eq
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^
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xor
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^=
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xor_eq
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[edit] Compatibility with C
The same words are defined in the C programming language in the include file <iso646.h> as macros. Because in C++ these are built into the language, the C++ version of <iso646.h>, as well as <ciso646>, does not define anything.
[edit] Digraphs and trigraphs
The following combinations of two and three characters (digraphs and trigraphs) are valid substitutions for their respective primary characters:
Primary | Digraph | Trigraph(until C++17) |
---|---|---|
{ |
<% |
??<
|
} |
%> |
??>
|
[ |
<: |
??(
|
] |
:> |
??)
|
# |
%: |
??=
|
\ |
??/
| |
^ |
??'
| |
| |
??!
| |
~ |
??-
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Note that trigraphs (but not digraphs) are parsed before comments and string literals are recognized, so a comment such as // Will the next line be executed?????/ will effectively comment out the following line, and the string literal such as "Enter date ??/??/??" is parsed as "Enter date \\??". |
(until C++17) |
When the parser meets the charater sequence <:: and the subsequent character is neither : nor >, the < is treated as a preprocessor token by itself and not as the first character of the alternative token <:. Thus std::vector<::std::string> won't be wrongly treated as std::vector[:std::string>. |
(since C++11) |
[edit] Keywords
and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq
[edit] Example
The following example demonstrates the use of several alternative tokens.
[edit] See also
C documentation for Alternative operator representations
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