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STL map problem

Hello,

I have following code. I wrote it in Borland C++ Builder 5.0.

#include <map>
#include <iostream>

using namespace std;

struct TVec
{
double x, y, z;
bool operator !=(const TVec& v2) const
{ return ((fabs(x-v2.x)>1e-12) || (fabs(y-v2.y)>1e-12) ||
(fabs(z-v2.z)>1e-12));}
};

typedef map<TVec, int, not_equal_to<TVec TMap;

int main()
{
TMap m;
TMap::iterator iter;

TVec v;

v.x=3.1; v.y=2.3; v.z=4.1;
m[v] = 32;
v.x=-3.1; v.y=2.3; v.z=4.1;
m[v]=45;
v.x=-3.25; v.y=2.3; v.z=4.1;
m[v] = 55;

cout<<"size = "<<m.size()<<endl;

v.x=3.1; v.y=2.3; v.z=4.1;
iter = m.find(v);
if (iter != m.end())
cout<<iter->second<<endl;

v.x=-3.1; v.y=2.3; v.z=4.1;
iter = m.find(v);
if (iter != m.end())
cout<<iter->second<<endl;

v.x=-3.25; v.y=2.3; v.z=4.1;
iter = m.find(v);
if (iter != m.end())
cout<<iter->second<<endl;

system("pause");
return 0;
}

After compilation we have on the screen :
size=3
32
45

However third element exsists in the map it isn't found by m.find(TVec)
(!!!)
I would be grateful for any suggestions.
Best regards, arkandor
Jun 27 '08 #1
3 2274
On Jun 24, 7:01*am, "arkandor" <arkando...@poczta.onet.plwrote:
Hello,

I have following code. I wrote it in Borland C++ Builder 5.0.

#include <map>
#include <iostream>

using namespace std;

struct TVec
*{
* *double x, y, z;
* *bool operator !=(const TVec& v2) const
* *{ return ((fabs(x-v2.x)>1e-12) || (fabs(y-v2.y)>1e-12) ||
(fabs(z-v2.z)>1e-12));}
*};

typedef map<TVec, int, not_equal_to<TVec TMap;

int main()
{
*TMap m;
*TMap::iterator iter;

*TVec v;

*v.x=3.1; v.y=2.3; v.z=4.1;
*m[v] = 32;
*v.x=-3.1; v.y=2.3; v.z=4.1;
*m[v]=45;
*v.x=-3.25; v.y=2.3; v.z=4.1;
*m[v] = 55;

*cout<<"size = "<<m.size()<<endl;

*v.x=3.1; v.y=2.3; v.z=4.1;
*iter = m.find(v);
*if (iter != m.end())
* cout<<iter->second<<endl;

*v.x=-3.1; v.y=2.3; v.z=4.1;
*iter = m.find(v);
*if (iter != m.end())
* cout<<iter->second<<endl;

*v.x=-3.25; v.y=2.3; v.z=4.1;
*iter = m.find(v);
*if (iter != m.end())
* cout<<iter->second<<endl;

*system("pause");
*return 0;

}

After compilation we have on the screen :
size=3
32
45

However third element exsists in the map it isn't found by m.find(TVec)
(!!!)
I would be grateful for any suggestions.
Best regards, arkandor
So you use the not_equal_to<TVecas the less_than compare for the
std::map, right?
which means whenever you have v1<v2, you also have v2<v1, where "<" is
what your map uses as a less_than compare ...
It doesn't suprise me all that you got non-sense result, because your
less_than compare doesn't make much sense.
Jun 27 '08 #2
On Jun 24, 1:01 pm, "arkandor" <arkando...@poczta.onet.plwrote:
I have following code. I wrote it in Borland C++ Builder 5.0.
#include <map>
#include <iostream>
using namespace std;
struct TVec
{
double x, y, z;
bool operator !=(const TVec& v2) const
{ return ((fabs(x-v2.x)>1e-12) || (fabs(y-v2.y)>1e-12) ||
(fabs(z-v2.z)>1e-12));}
};
typedef map<TVec, int, not_equal_to<TVec TMap;
std::map requires an ordering relationship, not an equivalence
relationship. (Not that you've implemented either; your
definition of != doesn't establish an equivalence relationship
either.)

From that point on, behavior is undefined.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34
Jun 27 '08 #3
So you use the not_equal_to<TVecas the less_than compare for the
std::map, right?
which means whenever you have v1<v2, you also have v2<v1, where "<" is
what your map uses as a less_than compare ...
It doesn't suprise me all that you got non-sense result, because your
less_than compare doesn't make much sense.

I've already solved this "problem". When I properly defined < operator
everything works fine. Thanks anyway.

arkandor
Jun 27 '08 #4

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