Alternative operators and tokens

C source code may be written in any 8-bit character set that includes the ISO 646:1983 {, }, [, ], #, \, ^, |, ~. To be able to use character encodings where some or all of these symbols do not exist (such as the German DIN 66003

Operator macros (C95)

There are alternative spellings for the operators that use non-ISO646 characters, defined in <iso646.h> as macros:

The characters & and !

There is no alternative spelling (such as eq) for the equality operator == because the character =

Alternative tokens (C95)

The following alternative tokens are part of the core language, and, in all respects of the language, each alternative token behaves exactly the same as its primary token, except for its spelling (the stringification operator can make the spelling visible). The two-letter alternative tokens are sometimes called "digraphs" (even though it is four letters long %:%:

Trigraphs (removed in C23)

The following three-character groups (trigraphs) are parsed before comments and string literals are recognized

Because trigraphs are processed early, 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 <stdio.h>
%:include <stdlib.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:>);
    %>
    else
    <%
       printf("Hello %s??/n", argc? argv??(42??'42??) : __FILE__);
    %>
 
    return EXIT_SUCCESS;
??>

Hello ./a.out

See also