What does the C++ standard say about using dollar signs in identifiers, such as Hello$World? Are they legal?
views:
844answers:
6
+13
A:
They are illegal. The only legal characters in identifiers are letters, numbers, and _. Identifiers also cannot start with numbers.
Nathaniel Flath
2009-06-01 20:56:56
FYI: Although illegal by the standard gcc usually allows them, see http://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar-Signs
lothar
2009-06-01 21:54:37
This is to allow backward compatability. It should not be used for any modern code.
Martin York
2009-06-02 00:40:51
A:
They are not legal in C++. However some C/C++ derived languages (such as Java and JavaScript) do allow them.
Zifre
2009-06-01 20:59:07
+11
A:
A c++ identifier can be composed of any of the following: _ (underscore), the digits 0-9, the letters a-z (both upper and lower case) and cannot start with a number.
There are a number of exceptions as C99 allows extensions to the standard (e.g. visual studio).
Kevin Loney
2009-06-01 20:59:17
That's silly that it is allow in VS. MS *always* has to make its own extensions to the standard...
Zifre
2009-06-01 21:03:28
Every major C++ compiler has a good handful of extensions. MS is not unique in that.
jalf
2009-06-01 21:14:17
You're mising Appendix E - (normative) "Universal-character-names for Identifiers" [extended-id]. However, this adds more letters (either accented or from different scripts), not symbols like $.
MSalters
2009-06-02 12:50:40
+1
A:
Illegal. I think the dollar sign and backtick are the only punctuation marks on my keyboard that aren't used in C++ somewhere (the "%" sign is in format strings, which are in C++ by reference to the C standard).
David Thornley
2009-06-01 21:00:23
+4
A:
Not legal, but many if not most of compilers support them, note this may depend on platform, thus gcc on arm does not support them due to assembly restrictions.
Artyom
2009-06-01 21:04:28
+1
A:
The relevant section is "2.8 Identifiers [lex.name]". From the basic character set, the only valid characters are A-Z a-z 0-9 and _. However, characters like é (U+00E9) are also allowed. Depending on your compiler, you might need to enter é as \u00e9, though.
MSalters
2009-06-02 12:55:53