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Re: selective linking of floating point support for *printf / *scanf
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Joey Ye <joey dot ye dot cc at gmail dot com>
- Cc: Thomas Preud'homme <thomas dot preudhomme at arm dot com>, Grissiom <chaos dot proton at gmail dot com>, Eric Blake <eblake at redhat dot com>, Joern Rennecke <joern dot rennecke at embecosm dot com>, GCC <gcc at gcc dot gnu dot org>, Joerg Wunsch <joerg_wunsch at uriah dot heep dot sax dot de>, <avr-libc-dev at nongnu dot org>, Andrew Burgess <andrew dot burgess at embecosm dot com>, "newlib at sourceware dot org" <newlib at sourceware dot org>
- Date: Tue, 2 Sep 2014 15:28:37 +0000
- Subject: Re: selective linking of floating point support for *printf / *scanf
- Authentication-results: sourceware.org; auth=none
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On Tue, 2 Sep 2014, Joey Ye wrote:
> Apparently newlib is not following this specification very well, as
> there are symbols like _abc_r defined every where in current newlib. I
> am not implying the spec should not be followed, but is newlib
> designed to have a loose spec for the single underscore?
Identifiers beginning with a single underscore are reserved with file
scope. This means an application cannot provide an external definition of
them, because such an external definition would have file scope. So it's
fine for the implementation to define such identifiers and use them in the
implementation of standard functions.
You do still need to be more careful with them than with _[_A-Z]*
identifiers. For example, you can't do
#define standard_function(x) _standard_function(x)
in your libc headers, because the user's application could legitimately
define a variable called _standard_function at block scope, then try to
call standard_function within that block. So in general it's safer to use
the double underscore in the implementation, unless there is some clear
reason to use the single underscore.
Joseph S. Myers