Alternative operator representations (since C95)
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.
[edit] 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) |
[edit] Digraphs and trigraphs
The following combinations of two and three characters (digraphs(C95) and trigraphs(C89)) 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|".
[edit] 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!".
%: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!
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C++ documentation for Alternative operator representations
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