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From "Martin Sebor (JIRA)" <j...@apache.org>
Subject [jira] Created: (STDCXX-995) __rw_new_capacity() doesn't control map, set
Date Fri, 18 Jul 2008 01:09:31 GMT
__rw_new_capacity() doesn't control map, set
--------------------------------------------

                 Key: STDCXX-995
                 URL: https://issues.apache.org/jira/browse/STDCXX-995
             Project: C++ Standard Library
          Issue Type: Bug
          Components: 23. Containers
    Affects Versions: 4.2.1, 4.2.0, 4.1.4, 4.1.3, 4.1.2
            Reporter: Martin Sebor
            Priority: Minor
             Fix For: 4.2.2


-------- Original Message --------
Subject: Re:  Controlling allocation policy of STL set.
Date: Thu, 17 Jul 2008 17:18:17 -0700 (PDT)
From: Dennis Handly <dhandly AT cup DOT hp DOT com>
To: sebor AT roguewave DOT com
CC: boris.gubenko AT hp DOT com, dhandly AT cup DOT hp DOT com, premanand.rao AT hp DOT com

We had this question from a user recently.  I was able to reverse engineer
how to do this with map/set.

Is this level of difficulty known?

Here is a link where we mention the info about {{__rw_new_capacity}}:
http://docs.hp.com/en/10946/libs.htm#container_alloc

I would be nice if we could just use the private typedef
{{std::map<K,V>::__rep_type}}.

Then we could just use:
{noformat}
#include <set>

typedef std::set<key_type> BlagPset;
typedef BlagPset::__rep_type BlagPtree;
// forward
template<>
inline size_t __rw::__rw_new_capacity<BlagPtree>(size_t size, BlagPtree const*);
{noformat}

Do you see any issues with making {{__rep_type}} public?

(Your Apache code still has it private but as {{_C_repT}}.)


===========================================================================
Do you know why the following code fragment does not work for me?
i.e it controls the vector's allocation policy as I expect, but not the
set's. I can believe there is some stupid mistake in there, but I have been
staring at it for a while now...

{noformat}
#include <stdio.h>
#include <vector>
#include <set>
class Blag { int a; };
std::vector<Blag*> bvec;
std::set<Blag*> bset;

template<>
inline size_t __rw::__rw_new_capacity<std::vector<Blag*> >(size_t size,
                                      std::vector<Blag*> const*) {
    if (size == 0) {
        fprintf(stderr, "Initial size will be 8 for vector\n");
        return 8;
    } else
        return size * 2;
}

template<>
inline size_t __rw::__rw_new_capacity<std::set<Blag*> >(size_t size,
                                       std::set<Blag*> const*) {
    if (size == 0) {
        fprintf(stderr, "Initial size will be 8 for set\n");
        return 8;
    } else
        return size * 2;
}
int main() {
    bset.insert(0);
    bvec.push_back(0);
}
{noformat}

===========================================================================
>From: Dennis Handly <dhandly AT cup DOT hp DOT com>

>Do you know why the following code fragment does not work for me?

Storage isn't allocated for the set but by the {{__rbtree}}.

>I can believe there is some stupid mistake in there

It isn't easy, you have to find the {{__rw_new_capacity call}}.

{noformat}
#include <stdio.h>
#include <vector>

class Blag { int a; };
typedef Blag* key_type;

// start kludge
#include <functional>
namespace __rw {
template <class _Key, class _Val, class _KeyOf, class _Comp, class _Alloc>
class __rb_tree;
template <class _TypeT, class _TypeU>
struct __ident;
} // namespace __rw
typedef __rw::__rb_tree<key_type, key_type, __rw::__ident<key_type, key_type>,
                        std::less<key_type>, std::allocator<key_type> >
                        BlagPtree;
// forward
template<>
inline size_t __rw::__rw_new_capacity<BlagPtree>(size_t size, BlagPtree const*);
// end kludge

#include <set>

typedef std::vector<key_type> BlagPvec;
typedef std::set<key_type> BlagPset;
BlagPvec bvec;
BlagPset bset;

template<>
inline size_t __rw::__rw_new_capacity<BlagPvec>(size_t size, BlagPvec const*) {
    if (size == 0) {
        fprintf(stderr, "Initial size will be 8 for vector\n");
        return 8;
    } else
        return size * 2;
}
// useless
template<>
inline size_t __rw::__rw_new_capacity<BlagPset>(size_t size, BlagPset const*) {
    if (size == 0) {
        fprintf(stderr, "Initial size will be 8 for set\n");
        return 8;
    } else
        return size * 2;
}
template<>
inline size_t __rw::__rw_new_capacity<BlagPtree>(size_t size, BlagPtree const*){
    if (size == 0) {
        fprintf(stderr, "Initial size will be 8 for tree\n");
        return 8;
    } else
        return size * 2;
}

int main() {
    bset.insert(0);
    bvec.push_back(0);
}
{noformat}

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