Alternative operator representations

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>.

Digraphs and trigraphs

The following combinations of two and three characters (digraphs(C95) and trigraphs(C89)) are valid substitutions for their respective primary characters:

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

%: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;
??>

Hello, World!