hash_multimap

[wysota]

You can always use a standard hash and keep there not single items, but lists of items. Something like: std::hash_map<std::list<Item> >

BTW. Are you sure hash_multimap is not available (I know it's not part of the standard, but for instance my system supports it)?
http://www.sgi.com/tech/stl/hash_multimap.html

[ct]

BTW. Are you sure hash_multimap is not available (I know it's not part of the standard, but for instance my system supports it)?

yes I think both g++ and VC++ has support for multimap but the usage varies. I needed something that would compile for both the compilers.
However, map and multimap should suffice my needs at the moment with O(logn) time complexity. I had mistakenly taken the time complexity of STL's map as O(n)..I was so wrong.. O (log n) is still fast..

[wysota]

STL on Linux is different than STL on Windows - these are completely different implementations, so you'll have differences in all other classes as well (probably including std::vector). The API should be the same on both platforms.

[ct]

Wow, you are right. The API of both g++ and vc++ is same; just have to insert the required headers. I have the same program working for both g++ and vc++ 2005 right now.
Here is the code:

//VC++
#include<iostream>
#include<cstdio>
#include<hash_map>
using namespace std;
using namespace stdext;
int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
 
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
 
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
 
 
    getchar();
    return 0;
}

//VC++
#include<iostream>
#include<cstdio>
#include<hash_map>
using namespace std;
using namespace stdext;
int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
    
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
    
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
   
    
    getchar();
    return 0;
}

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//g++
#include<iostream>
#include<cstdio>
#include<ext/hash_map>
using namespace std;
using namespace __gnu_cxx;
int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
 
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
 
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
 
 
    getchar();
    return 0;
}

//g++
#include<iostream>
#include<cstdio>
#include<ext/hash_map>
using namespace std;
using namespace __gnu_cxx;
int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
    
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
    
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
   
    
    getchar();
    return 0;
}

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However I am running into some problem with hash_map<string,string> for both the compilers. I am sure there is some compare function that needs to be defined for strings or is there something already available ?

[ct]

BTW, how can I combine both these files into one so that both the compilers can compile it. Is there some flag that needs to be checked to find out if the compiler is VC++ or g++ ?

[spud]

#ifdef Q_CC_MSVC
#include<hash_map>
using namespace stdext;
#endif
 
#ifdef Q_CC_GNU
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif

#ifdef Q_CC_MSVC
#include<hash_map>
using namespace stdext;
#endif

#ifdef Q_CC_GNU
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif

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[ct]

#ifdef Q_CC_MSVC
#include<hash_map>
using namespace stdext;
#endif
 
#ifdef Q_CC_GNU
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif

#ifdef Q_CC_MSVC
#include<hash_map>
using namespace stdext;
#endif

#ifdef Q_CC_GNU
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif

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That certainly didn't work. Is that some QT preprocessor that does the same thing? I opened up the glut.h file and saw how they have done it so I got upto here.

#include<iostream>
#include<cstdio>
 
#if defined(__MINGW32__)
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif
 
#if defined(_MSC_VER)
#include<hash_map>
using namespace stdext;
#endif
 
#include<iostream>
#include<cstdio>
 
using namespace std;
 
int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
 
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
 
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
 
 
    getchar();
    return 0;
}

#include<iostream>
#include<cstdio>

#if defined(__MINGW32__)
#include<ext/hash_map>
using namespace __gnu_cxx;
#endif

#if defined(_MSC_VER)
#include<hash_map>
using namespace stdext;
#endif

#include<iostream>
#include<cstdio>

using namespace std;

int main(int argc,char** argv)
{   
    hash_map<int,int> mapping;
    hash_map<int,int>::const_iterator miter;
    
    mapping.insert(pair<int,int>(1,100));
    mapping.insert(pair<int,int>(2,200));
    miter = mapping.find(1);
    
    if(miter == mapping.end())
        cout << "Not found";
    else
       cout << miter->first << " = " << miter->second;
   
    
    getchar();
    return 0;
}

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The preprocessors have always confused me a bit. Is there a list of all the preprocessors that can be used (at least the more common ones ). Can anyone point to some good resource about types of general preprocessors or may be list some common ones out here ?