Digest for comp.lang.c++@googlegroups.com - 4 updates in 3 topics

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• something happened to malloc? - 1 Update
• mysterious destructors - 2 Updates
• mysterious destructors - 1 Update

something happened to malloc?

Robert Wessel <robertwessel2@yahoo.com>: Feb 19 11:32AM -0600 On Wed, 18 Feb 2015 09:29:15 +0100, Torsten Mueller   >In my application I use also boost (1.57). And boost has an own cstdlib >header. Could this be the reason?   >Has anyone had this problem in the last time, malloc is undefined?     Could you be seeing a namespace problem? While cstdlib mostly includes stdlin.h, it does put most items into the std: namespace. Perhaps the headers got tightened up recently to not put those functions in both std: and the global namespace?

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mysterious destructors

Ian Collins <ian-news@hotmail.com>: Feb 19 05:37PM +1300 Stefan Ram wrote:   > int main() > { ::std::unique_ptr< c >o( f( &o )); o->print(); }   > Does this program violate any rule of C++?   I'd pick passing the address of an uninitialised object (o) to f to be UB.   By the way, why to you keep adding superfluous scoping, but remove the white-space that would make the code readable? I'm sure there are some obscure corner cases that may justify the scoping, but Usenet posts aren't one of them!   -- Ian Collins

Paavo Helde <myfirstname@osa.pri.ee>: Feb 18 10:46PM -0600 ram@zedat.fu-berlin.de (Stefan Ram) wrote in   > int main() > { ::std::unique_ptr< c >o( f( &o )); o->print(); }   > Does this program violate any rule of C++?   I am pretty sure it does. The program takes the address of o before it is constructed (this is OK in principle), and then goes on to assign something to this location, still before the o object has been constructed - this is definitely UB with a non-trivial class like std::unique_ptr.   From the standard (12.7):   "For an object with a non-trivial constructor, referring to any non- static member or base class of the object before the constructor begins execution results in undefined behavior."   The crucial point here is that std::unique_ptr has a non-trivial constructor. Note that in C the answer may be different because in C there is no such thing as a non-trivial constructor.   Cheers Paavo

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mysterious destructors

ram@zedat.fu-berlin.de (Stefan Ram): Feb 19 04:04AM > o->print(); > o = std::unique_ptr<c>(new c( 2 )); /* overwrite */ > o->print(); }   Actually, I wanted to observe how C++ interprets an example someone posted into the C newsgroup recently. Here is my attempt of a translation into C++:   #include <iostream> #include <ostream> #include <memory>   struct c /* this struct is as above (as before) */ { int v; c( int const x ): v( x ) { ::std::cout << "constructor of instance #" << v << ".\n"; } ~c(){ ::std::cout << "destructor of instance #" << v << ".\n"; } void print(){ ::std::cout << "I am instance #" << v << ".\n"; }};   ::std::unique_ptr< c >f( ::std::unique_ptr< c >* p ) { *p = ::std::make_unique< c >( 2 ); /* <- sequence point! (semicolon) */ return ::std::make_unique< c >( 1 ); }   int main() { ::std::unique_ptr< c >o( f( &o )); o->print(); }   Does this program violate any rule of C++?

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