zhx...@gmail.com napsal:

Here is a program, I want to change the way which a map use to order
elements.

struct sizemore
{
bool operator()(const wstring &s1,const wstring &s2)
{
return s1.size()>s2.size();
}
};

int dictinput(const char *filename,map<wstring,wstring> &mwdict())
{
...
}

int main()
{
map<wstring,wstring> mwdict(sizemore());
dictinput("filename",mwdict);
}

But I receive a message:
error C2664: 'dictinput' : cannot convert parameter 2 from
'std::map<_Kty,_Ty> (__cdecl *)(sizemore (__cdecl *)(void))' to
'std::map<_Kty,_Ty> &(__cdecl *)(void)'

I'm always puzzled with parameters of function.
Could some one give me some advices?
Thanks a lot.

You need to specify comparation as 3rd parameter of template std::map.
See example below:

#include <iostream>

#include <map>
#include <string>

template<typename T>
struct CmpBySize
{
bool operator()(const T& s1, const T& s2) const
{
return s1.size() < s2.size();
}

};

typedef
std::map<std::string, std::string, CmpBySize<std::string> >
MapStrStr;

int main()
{
MapStrStr m;
m["aaa"] =3D "3 x a";
m["bb"] =3D "2 x b";
m["z"] =3D "1 x z";

const MapStrStr::const_iterator end =3D m.end();
for (MapStrStr::const_iterator i =3D m.begin(); i !=3D end; ++i)
{
std::cout << "m[\"" << i->first << "\"] =3D \"" << i->second <<
"\"\n";
}



}