Re: libstdc++/5133: Problems with toupper

[Martin Sebor <sebor@roguewave.com>]

The following reply was made to PR libstdc++/5133; it has been noted by GNATS.

From: Martin Sebor <sebor@roguewave.com>
To: gcc-gnats@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/5133: Problems with toupper
Date: Sun, 16 Dec 2001 18:54:22 -0700

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=5133
 
 None of the programs in this PR is well-formed for at least two reasons:
 
     1. The first two refer to ::tolower or tolower without either first
        #including <ctype.h>, or #including <cctype> *and* bringing              
 std::tolower into the global namespace via a using declaration
        or directive.
 
     2. The four-argument overload of std::transform() is a template
        that expects a unary function [object] as its last argument,
        i.e., a class type that defines operator() or a one argument
        function with extern "C++" linkage. None of the two overloads
        of std::tolower is likely to be such a function (the unary
        version that's intended to be used is likely to have an extern
        "C" linkage since it's a C library function). In fact, they are
        known to be extern "C" in glibc on Linux, the reported platform.
 
 Paolo's suggested change suffers from a variant of 1, except that it
 doesn't qualify the name at all. It has the same problem as 2. IMO,
 there are two reasons why this example compiles with gcc: one of the
 headers inadvertently introduces the unary function tolower into the
 global namespace, and the compiler fails to diagnose the incompatibility
 of an extern "C" function with a pointer to an extern "C++" function.
 
 The short story is that you cannot portably pass a function declared
 in one of the C++ C library headers (such as <cctype> or the deprecated
 <ctype.h>) as a template argument to a function template, since the
 linkage of the latter requires that that the argument have C++ linkage
 which is not guaranteed by the C++ Standard. For this reason, the
 example is Jossutis' book is unportable and ill-formed on all platforms
 I'm familiar with.
 
 Regards
 Martin