C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  overriding global new and delete + STL          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message shoosh Guest Posted: Thu Jan 27, 2005 8:58 pm    Post subject: overriding global new and delete + STL hi for my application under VC6 I need to implement my own memory manager which overrides the global new and delete operators and which Do Not use the normal free() and malloc(). it seemed to work fine on its own but when I tried to use say 'cout' or 'cerr' from STL the tester crashed upon termination. using some breakpoints I found out that when I make use of 'cerr' in the program, there is a call to my override of delete which do not correspond to any call to my override to new. infact, with just a main() saying: int main() { cerr << "boo"; return 0; } all I got was a break in my operator delete and no breaks at all in my operator new. how is the memory allocated if now by using my operator new? where does this pointer come from? does anyone know anything about this issue? any help? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Maeder Guest Posted: Fri Jan 28, 2005 12:40 am    Post subject: Re: overriding global new and delete + STL shoosh <shoosh4242 (AT) walla (DOT) co.il> writes: Quote: using some breakpoints I found out that when I make use of 'cerr' in the program, there is a call to my override of delete which do not correspond to any call to my override to new. infact, with just a main() saying: int main() { cerr << "boo"; return 0; } Please post the entire program, including the overloaded (de)allocation functions. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dietmar Kuehl Guest Posted: Fri Jan 28, 2005 11:14 am    Post subject: Re: overriding global new and delete + STL shoosh wrote: Quote: how is the memory allocated if now by using my operator new? I'm a little bit rusty on replacing operators new and operator delete but I could imagine that the memory is allocated with the 'nothrow' version of 'operator new()' but deleted with the normal 'operator delete()'. That is, you might want to add the following function: /**/ void operator new(std::size_t sz, std::nothrow const&) throw() /**/ { /**/ ... /**/ } A brief glance at the standard just states that both version of 'operator new()' are replaceable but there is no statement that they need to be replaced together. Of course, this makes for an interesting problem: as an implementer of the standard C++ library I would probably implement the throwing version in terms of the not throwing one. Of course, if a user replace the throwing version, 'operator delete()' may get called with memory not allocated from his replacement version because the nothrow version is called somewhere. Since there is no way to detect whether the not throwing one is replaced, there is no chance to do it correctly: even if the operators are implemented the other way around things could break. All the user needs to do is to replace the 'operator new()'. Probably the standard is defective if it does not state that both versions of 'operator new()' need to be replaced if one is replaced. -- <mailto:dietmar_kuehl (AT) yahoo (DOT) com> <http://www.dietmar-kuehl.de/> <http://www.contendix.com> - Software Development & Consulting [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top shoosh Guest Posted: Fri Jan 28, 2005 11:29 am    Post subject: Re: overriding global new and delete + STL the whole new Memory manager I wrote it not relevant to the discussion and is too big to post. yet the problem I describe can be recreated simply, like so: #include <stdio.h> #include <iostream.h> #include <stdlib.h> void *operator new( size_t stAllocateBlock ) { printf("Memory block %d allocated for %d bytesn" ,++cBlocksAllocated, stAllocateBlock); return NULL; } // User-defined operator delete. void operator delete( void *pvMem ) { printf("Memory block %d deallocatedn", --cBlocksAllocated); } int main( int argc, char *argv[] ) { cout << "YEA!" << endl; return 0; } running this code results in the following output: YEA! Memory block -1 deallocated Memory block -2 deallocated which means the my override of delete ran twice and the override of new did not ran at all. if I loose the 'cout' line and the #include nothing. "Thomas Maeder" <maeder (AT) glue (DOT) ch> wrote Quote: shoosh <shoosh4242 (AT) walla (DOT) co.il> writes: using some breakpoints I found out that when I make use of 'cerr' in the program, there is a call to my override of delete which do not correspond to any call to my override to new. infact, with just a main() saying: int main() { cerr << "boo"; return 0; } Please post the entire program, including the overloaded (de)allocation functions. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Paul Guest Posted: Sat Jan 29, 2005 4:28 am    Post subject: Re: overriding global new and delete + STL "shoosh" <shoosh4242 (AT) walla (DOT) co.il> wrote Quote: the whole new Memory manager I wrote it not relevant to the discussion and is too big to post. yet the problem I describe can be recreated simply, like so: #include <stdio.h #include Use <iostream.h> is non-standard, so there is no telling what this thing does for some cases. <iostream> is the standard header, and will exhibit (or should exhibit) standard-conforming behavior. Once you do this, you have to remember that cout is now in the std namespace, and you must adjust your code accordingly. Paul McKenzie [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top msalters Guest Posted: Sat Jan 29, 2005 4:45 am    Post subject: Re: overriding global new and delete + STL Dietmar Kuehl wrote: Quote: A brief glance at the standard just states that both version of 'operator new()' are replaceable but there is no statement that they need to be replaced together. Of course, this makes for an interesting problem: as an implementer of the standard C++ library I would probably implement the throwing version in terms of the not throwing one. Of course, if a user replace the throwing version, 'operator delete()' may get called with memory not allocated from his replacement version because the nothrow version is called somewhere. Since there is no way to detect whether the not throwing one is replaced, there is no chance to do it correctly: even if the operators are implemented the other way around things could break. All the user needs to do is to replace the 'operator new()'. Probably the standard is defective if it does not state that both versions of 'operator new()' need to be replaced if one A footnote would be nice, but if I replace one to forward to the other, I would like it to work. This logically works (when the allocation succeeds, the same value is returned and delete doesn't care how it got that value) but your extra wording would prohibit it. Not sure if there's a good reason to do so, but it would work as long as any implementor is reasonably careful. The tricky point for implementors is that if the built-in throwing unconditionally forwards to the non-throwing, and the user replaces only that one to forward to the throwing, you end up with a loop. So an implementor probably has to call some shared __new() (or malloc()) from both versions of the default operator new. With this implementation, replacing either version of new to forward to the other will work ok, including deletion. Regards, Michiel Salters [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dietmar Kuehl Guest Posted: Sat Jan 29, 2005 9:41 am    Post subject: Re: overriding global new and delete + STL shoosh wrote: Quote: #include <iostream.h I don't know whether it is related to your problem but you should get rid of this header as soon as possible: it is non-standard. You should use /**/ #include (i.e. without the ".h") instead. Other than that, I would guess that you should also replace the "nothrow" version of 'operator new()'. -- <mailto:dietmar_kuehl (AT) yahoo (DOT) com> <http://www.dietmar-kuehl.de/> <http://www.contendix.com> - Software Development & Consulting [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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