VC’s "evil" extension: $


In C++, only a few characters can be used as part of the identifier.


identifier:
    identifier-nondigit
    identifier identifier-nondigit
    identifier digit
identifier-nondigit:
    nondigit
    universal-character-name
    other implementation-defined characters
nondigit: one of
    a b c d e f g h i j k l m
    n o p q r s t u v w x y z
    A B C D E F G H I J K L M
    N O P Q R S T U V W X Y Z _
digit: one of
    0 1 2 3 4 5 6 7 8 9


However, there is one exception in VC. The “evil” extension allows “$” to be valid in identifier name.


It is used inside “sal.h” (Source Annotation Language). Like:

#define _$valid       Valid=SA_Yes


But I have no idea why they need “$” 😛

Comments (2)

  1. LordHunter317 says:

    Lots of legacy C (and C++) code uses functions that have ‘$’ within the function name.  Many of the system calls on OpenVMS have a ‘$’ as part of their name, and it was a common naming convention in a lot of FORTRAN code.   As such, support for ‘$’ is a pretty common extension even today.  I still have a lot of code that requires such an extension.

    As to why that particular place uses it, no clue.

  2. xiangfan says:

    Hi LordHunter317:

       Thanks for sharing the information.

       This reminds me the deprecation attempt of trigraph in C++0x (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2910.pdf)

       Many "obselete" features / language extensions are extensively used 🙂