c++ - Using struct as KEY and VALUE for map. find() operation giving error -

code in c++:

#include <iostream> #include <map> #include <string>  using namespace std;  struct keyinfo {   string key1;    string key2;     bool keyinfo::operator <(keyinfo &a) const     { return ((this->key1<a.key1)&&(this->key2<a.key2)); } };  struct valueinfo {    int value1;    int value2;    int value3;     valueinfo(const int a,const int b,const int c) :      value1(a),value2(b),value3(c) {} }; typedef std::map<keyinfo, valueinfo> maptype;  int main() {   maptype tmap;   keyinfo k;   k.key1="main";   k.key2="i";   valueinfo v(-2,-3322,9000);    tmap.insert(maptype::value_type(k,v));   maptype::iterator it1=tmap.find(k);   it1=tmap.find(k);   if(it1!=tmap.end())     std::cout<<"success(k): "<<it1->second.value2<<std::endl;    keyinfo e;   e.key1="main";   e.key2="j";   //tmap.insert(std::pair<keyinfo,valueinfo>(e,v));   maptype::iterator it2=tmap.find(e);   if (it2!=tmap.end())      std::cout<<"success(e): "<<(it2->second).value3<<std::endl;    cin.get();   return 0;  } 

when compile code gave me error:

error c2679: binary '<' : no operator found takes right-hand operand of type 'const keyinfo1' (or there no acceptable conversion)

please let me know i'm going wrong? highly appreciated. thanks.

i have tried implement own operator , used in map<>, code looks follows:

#include <iostream> #include <map> #include <string>  using namespace std;  struct keyinfo {   string key1;    string key2;     /*bool keyinfo::operator()(keyinfo const& left,keyinfo const& right) const{       return ((left.key1<right.key1)&&(left.key2<right.key2));   }*/ };  struct lesscomparer{     bool operator()(keyinfo const& left,keyinfo const& right) const{         return !(left.key1==right.key1 && left.key2==right.key2);     } };  struct valueinfo {    int value1;    int value2;    int value3;     valueinfo(const int a,const int b,const int c) :      value1(a),value2(b),value3(c) {} }; typedef std::map<keyinfo, valueinfo, lesscomparer> maptype;  int main() {   maptype tmap;   keyinfo k;   k.key1="main";   k.key2="i";   valueinfo v(-2,-3322,9000);    tmap.insert(maptype::value_type(k,v));   maptype::iterator it1=tmap.find(k);   it1=tmap.find(k);   if(it1!=tmap.end())     std::cout<<"success(k): "<<it1->second.value2<<std::endl;    keyinfo e;   e.key1="main";   e.key2="j";   //tmap.insert(std::pair<keyinfo,valueinfo>(e,v));   maptype::iterator it2=tmap.find(e);   if (it2!=tmap.end())      std::cout<<"success(e): "<<(it2->second).value3<<std::endl;    cin.get();   return 0;  } 

here i'm using operator() return 0 iff both key1 , key2 of left , right equal. think same way map::less works, mean return false if equality condition satisfied.

it works fine in first case i.e. tmap.find(k) same key found. during call in second case i.e. tmap.find(e) pops error saying:

"debug assertion failed" expression: invalid operator < 

your declaration of operator< off.

struct keyinfo {   string key1;    string key2;     bool keyinfo::operator <(keyinfo &a) const     { return ((this->key1<a.key1)&&(this->key2<a.key2)); } }; 

... , several reasons:

1. it error prefix declaration class name within class. should if define outside class. compilers laxist, standard says should not this.
2. the reason cannot compile operator< should accept both operands either values (for simple things) or const&. here forgot const a.
3. the definition incorrect, operator< has semantics off properties of antisymmetry not respected.
4. it recommended binary operators declared free functions outside class.

all in all, correct declaration , definition are:

struct keyinfo {   std::string key1;   std::string key2; };  inline bool operator<(keyinfo const& left, keyinfo const& right) {   if (left.key1 < right.key1) { return true; }   if (left.key1 > right.key1) { return false; }   return left.key2 < right.key2; } 

if can use boost, "simple" way implement is:

inline bool operator<(keyinfo const& left, keyinfo const& right) {   return boost::tie(boost::cref(left.key1) , boost::cref(left.key2))        < boost::tie(boost::cref(right.key1), boost::cref(right.key2)); }