std::map<,>, xtree and find

I am working on an unmannaged C++ application in Visual Studio 2003. The application is using STL map class.

std::map<ApxString, CGPO> GPOs;
GPODataFactory.GetGPOs( pContext, GPOs);
std::map<ApxString, CGPO>::iterator GPODataIter = GPOs.find( GPOGroupKey)

GPOGroupKey is of type ApxString of course and it was initialized to "T" earlier in the program.

When I go through the debbuger in the GetGPOs function and use the find function, I find the row I am looking for. However, when I go through the find function after I exit the GetGPOs function, I don't find it.

As I stepped into the find function,

iterator find(const key_type& _Keyval)
{ // find an element in mutable sequence that matches _Keyval
iterator _Where = lower_bound(_Keyval);
return (_Where == end() || this->comp(_Keyval, _Key(_Where._Mynode())) end() : _Where);
}

where the lower_bound function ends up calling the following xtree function

_Nodeptr _Lbound(const key_type& _Keyval) const
{ // find leftmost node not less than _Keyval
   _Nodeptr _Pnode = _Root();
   _Nodeptr _Wherenode = _Myhead; // end() if search fails
   while (!_Isnil(_Pnode))
      if (this->comp(_Key(_Pnode), _Keyval))
         _Pnode = _Right(_Pnode); // descend right subtree
      else
      { // _Pnode not less than _Keyval, remember it
         _Wherenode = _Pnode;
         _Pnode = _Left(_Pnode); // descend left subtree
      }
   return (_Wherenode); // return best remembered candidate
}

and this->comp(_Key(_Pnode), _Keyval) calls the following in the functional standard header

// TEMPLATE STRUCT less
template<class _Ty>
struct less
: public binary_function<_Ty, _Ty, bool>
{ // functor for operator<
   bool operator()(const _Ty& _Left, const _Ty& _Right) const
   { // apply operator< to operands
      return (_Left < _Right);
   }
};

I found that the difference was on the return(_Left < _Right) line. Although the _Left and _Right values are the same both times ("O" < "T"), I consistently get a true evaluation the first time (which is correct) and false the second time (which is incorrect). This makes no sense. O is 4F and T is 54 in hex.

Any comments are appreciated.

Thanks in advance,
-stephen

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std::map<,>, xtree and find

andyr2005
Write your own compare function:

struct S_COMPARE_ApxString
{
bool operator() (const ApxString &l, const ApxString &r) const
      {
       // Do what ever you need to compare it
...
      }
};

typedef std::map<ApxString, CGPO, S_COMPARE_ApxString> MYCLASS;
vnilo
Hello Martin,

Thanks for the response. That's what I initially thought, but ApxString doesn't have a less than operator. It is just returning m_pData->m_pchData to the less function in the functional standard header using the following function.

ApxString::operator const char *() const
{
   if (m_pData == 0)
   {
      return 0;
   }
   else
   {
      return m_pData->m_pchData;
   }
}

m_pchData is of type char *.

Regards,
-stephen
Angie28
Unless the debbuger is reporting icorrectly, the key value hasn't changed.

First pass:
_Left
{m_pData=0x02220000 {m_pchData=0x02230000 "O" m_dwRefCount=2 m_dwBufferSize=3 } }
    __vfptr: 0x0032a0c0 const ApxString::`vftable'
    m_pData: 0x02220000 {m_pchData=0x02230000 "O" m_dwRefCount=2 m_dwBufferSize=3 }

_Right
{m_pData=0x02240000 {m_pchData=0x02250000 "T" m_dwRefCount=3 m_dwBufferSize=3 } }
    __vfptr: 0x0032a0c0 const ApxString::`vftable'
    m_pData: 0x02240000 {m_pchData=0x02250000 "T" m_dwRefCount=3 m_dwBufferSize=3 }

Second pass:
_Left
{m_pData=0x02220000 {m_pchData=0x02230000 "O" m_dwRefCount=2 m_dwBufferSize=3 } }
    __vfptr: 0x0032a0c0 const ApxString::`vftable'
    m_pData: 0x02220000 {m_pchData=0x02230000 "O" m_dwRefCount=2 m_dwBufferSize=3 }
_Right
{m_pData=0x021b0000 {m_pchData=0x021e0000 "T" m_dwRefCount=4 m_dwBufferSize=3 } }
    __vfptr: 0x0032a0c0 const ApxString::`vftable'
    m_pData: 0x021b0000 {m_pchData=0x021e0000 "T" m_dwRefCount=4 m_dwBufferSize=3 }

Thanks,
-stephen
Frosty1_4me

Sounds good. Thanks for the help Martin.
GradyMeng
Is there a chance that you operator< for ApxString doesn't work correct.
James Downey
Well, Martin, you're right. The < operator is not working correctly with ApxString. If I do

ApxString key1 = "A";
ApxString key2 = "B";

if (key1 < key2)
{
...
}

It doesn't use the value of the string but the memory address of the m_pchData which is weird because if I step into the if statement, it shows that it is returning m_pData->m_pchData from ApxString::operator const char *() const.

I contacted the developer of ApxString but any help is appreciated.

thanks,
-stephen
ZaDDaZ
But is there a chance that in the lifetime this value changes In this case you get problems. The key value must be persistent!
std::map<,>, xtree and find

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