Alternative operator representations

 

C++

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Alternative representations of operators

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Fold expression(C++17)

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User-defined conversion

 

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.

Alternative tokens

There are alternative spellings for several operators defined as tokens with special meaning in the C++ standard.

Primary	Alternative
&&	and
&=	and_eq
&	bitand
|	bitor
~	compl
!	not
!=	not_eq
||	or
|=	or_eq
^	xor
^=	xor_eq

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.

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)
{	<%	??<
}	%>	??>
[	<:	??(
]	:>	??)
#	%:	??=
\		??/
^		??'
|		??!
~		??-

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)

Keywords

and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq

Example

The following example demonstrates the use of several alternative tokens.

Run this code

%:include <iostream>
 
int main(int argc, char *argv<::>) 
<%
    if (argc > 1 and argv<:1:> not_eq NULL) <%
        std::cout << "Hello, " << argv<:1:> << '\n';
    %>
%>

See also

C documentation for Alternative operator representations