Alternative operator representations (since C99)

 

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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), there are two possibilities: alternative spellings of operators that use these characters or special combinations of two or three ISO 646 compatible characters that are interpreted as if they were a single non-ISO 646 character.

Alternative spellings

There are alternative spellings for several operators defined in <iso646.h>.

Defined in header <iso646.h>
Primary	Alternative
&&	and (macro constant)
&=	and_eq (macro constant)
&	bitand (macro constant)
|	bitor (macro constant)
~	compl (macro constant)
!	not (macro constant)
!=	not_eq (macro constant)
||	or (macro constant)
|=	or_eq (macro constant)
^	xor (macro constant)
^=	xor_eq (macro constant)

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

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 "What's going on??!" is parsed as "What's going on|".

Example

The following example demonstrates alternative operator spellings from the <iso646.h> header as well as use of digraphs and trigraphs.

The space character in the first command-line argument, argv[1], requires the quotation marks: ", World!".

Run this code

%:include <stdlib.h>
%:include <stdio.h>
%:include <iso646.h>
 
int main(int argc, char** argv)
??<
    if (argc > 1 and argv<:1:> not_eq NULL)
    <%
       printf("Hello%s\n", argv<:1:>);
    %>
 
    return EXIT_SUCCESS;
??>

Possible output:

Hello, World!

C++ documentation for Alternative operator representations