Maps and constructors and other crap

**~~nickname_changed~~** · 09-06-2003

Grettings and salutations :)

I have the following two classes:

Code:

//------------------------------------------
//  VHSTATS Class
//------------------------------------------
class VHSTATS
{
public:
    VHSTATS();
    VHSTATS(VIRTUALHOST);
    map <string, int> PageRequests;
    unsigned long NumberOfRequests;
    unsigned long BytesSent; 
    VIRTUALHOST ThisVH;  // VIRTUALHOST is a structure with info and strings and crap
};

//------------------------------------------
//  STATS Class
//------------------------------------------
class STATS
{
  public:
    STATS(); 
    bool WriteStatsFile();
    
    unsigned long NumberOfRequests;
    unsigned long TotalNumberOfRequests;
    unsigned long BytesSent;
    unsigned long TotalBytesSent;
    string LastRestart; 
    map <string, int> PageRequests;
    map <VIRTUALHOST, VHSTATS> VirtualHosts;basis 
};

STATS::STATS() looks something like this:

Code:

STATS::STATS()
{
    // 1: Load all the virtual hosts
    int X = 0;
    while (VHI.HostNumbers[X].empty() == false)
    {
        string Name = VHI.HostNumbers[X];
        VHSTATS TempVHStats(VHI.Host[Name]); 
        VirtualHosts[VHI.Host[Name]] = TempVHStats;
    }
    .....

Where VHI.Host is an map of strings to VIRTUALHOST's, and VHI.HostNumbers is a map of integers to strings (that match the strings used by VHI.Host).

When I try to compile, VC++ gives me this:

Code:

stats.cpp
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::multimap<_K,_Ty,_Pr,_A> &,const class std::multimap<_K,_Ty,_Pr,_A> &)' : could not deduce template argument for 'const
 class std::multimap<_K,_Ty,_Pr,_A> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::map<_K,_Ty,_Pr,_A> &,const class std::map<_K,_Ty,_Pr,_A> &)' : could not deduce template argument for 'const class std
::map<_K,_Ty,_Pr,_A> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::_Tree<_K,_Ty,_Kfn,_Pr,_A> &,const class std::_Tree<_K,_Ty,_Kfn,_Pr,_A> &)' : could not deduce template argument for 'c
onst class std::_Tree<_K,_Ty,_Kfn,_Pr,_A> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::basic_string<_E,_Tr,_A> &,const _E *)' : could not deduce template argument for 'const class std::basic_string<_E,_Tr,
_A> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const _E *,const class std::basic_string<_E,_Tr,_A> &)' : could not deduce template argument for 'const  *' from 'const class VIRTUALHO
ST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::basic_string<_E,_Tr,_A> &,const class std::basic_string<_E,_Tr,_A> &)' : could not deduce template argument for 'const
 class std::basic_string<_E,_Tr,_A> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const class std::reverse_iterator<_RI,_Ty,_Rt,_Pt,_D> &,const class std::reverse_iterator<_RI,_Ty,_Rt,_Pt,_D> &)' : could not deduce te
mplate argument for 'const class std::reverse_iterator<_RI,_Ty,_Rt,_Pt,_D> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2784: 'bool __cdecl std::operator <(const struct std::pair<_T1,_T2> &,const struct std::pair<_T1,_T2> &)' : could not deduce template argument for 'const struct std::pair<
_T1,_T2> &' from 'const class VIRTUALHOST'
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : error C2676: binary '<' : 'const class VIRTUALHOST' does not define this operator or a conversion to a type acceptable to the predefined operator
        C:\Program Files\Microsoft Visual Studio\VC98\INCLUDE\functional(86) : while compiling class-template member function 'bool __thiscall std::less<class VIRTUALHOST>::operator ()(const class VIRTUALHOST &,const class VIRTUALHOST &) const'
Error executing cl.exe.

SWEBS.exe - 9 error(s), 0 warning(s)

All of them seem to be in files which I have not touched. Can anyone see what it is I must have done wrong? I'm stumped on this one, it should work fine :( Thanks for any help!

**ripper079** · 09-06-2003

When you are using user defind objects as elemets in your (STL)containers they must satify some requirements like

Element must implement a default constructor
Element must be copyable (implement copy constructor)
Element must be assignable (overload assignment operator =)
Element must be destoyable (implement destructor)
Element must be compareable (operator ==, operator <, operator > ...)

Of course doesn´t you need to implement all these requirement (but this is recommended), because different container requires different requirements. E.i If you are using VIRTUALHOST objects in a stack there is no need for compareison but in a map there is.

Make your VIRTUALHOST- and VHSTATSobjects compareable(I think that it should be enough with operator<) and your problem should be solved.

P.S. Don´t rely on that the compiler will create it´s defaults version of constructor, destructor, operator==... in most cases this isn´t enough and the containers may not behave as it should.

**~~nickname_changed~~** · 09-06-2003

Thanks ripper079, I did what you said and it compiled perfectly!! Thanks a lot!

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