c ++中的代码如下：
#include<iostream>
#include<string>
#include<set>
using namespace std;
class data{
int i;
float f;
char c;
public:
bool operator()( data const& a1, data const& a2 ) const{
return( a1.i < a2.i ||
(!(a1.i > a2.i) && (a1.f < a2.f)) ||
(!(a1.i > a2.i) && !(a1.f > a2.f) && (a1.c < a2.c)));
};
data();
data(int i,float f,char c);
int geti();
};
int data::geti(){
return i;
};
data::data(int i,float f,char c){
this->i=i;
this->f=f;
this->c=c;
};
int main(){
set<data> s;
set<data>::iterator it;
s.insert(data(1,1.3,'a'));
s.insert(data(2,2.3,'b'));
s.insert(data(3,3.3,'c'));
if((it=s.find(data(1,1.3,'a')))!=s.end())
cout<<(*it).geti();
cin.get();
return 0;
}
此问题是在C++ set Question
中建议的修改之后在编译时，它会从.. \ vc \ include \ functional和.. \ vc \ include \ xtree
中给出JUNK错误请帮我解决错误。 感谢。
错误：
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\xtree(1372) : see declaration of 'std::operator <'
1> c:\program files\microsoft visual studio 8\vc\include\functional(142) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const'
1> with
1> [
1> _Ty=data
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\set(60) : see reference to class template instantiation 'std::less<_Ty>' being compiled
1> with
1> [
1> _Ty=data
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\xtree(26) : see reference to class template instantiation 'std::_Tset_traits<_Kty,_Pr,_Alloc,_Mfl>' being compiled
1> with
1> [
1> _Kty=data,
1> _Pr=std::less<data>,
1> _Alloc=std::allocator<data>,
1> _Mfl=false
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\xtree(68) : see reference to class template instantiation 'std::_Tree_nod<_Traits>' being compiled
1> with
1> [
1> _Traits=std::_Tset_traits<data,std::less<data>,std::allocator<data>,false>
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\xtree(94) : see reference to class template instantiation 'std::_Tree_ptr<_Traits>' being compiled
1> with
1> [
1> _Traits=std::_Tset_traits<data,std::less<data>,std::allocator<data>,false>
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\xtree(112) : see reference to class template instantiation 'std::_Tree_val<_Traits>' being compiled
1> with
1> [
1> _Traits=std::_Tset_traits<data,std::less<data>,std::allocator<data>,false>
1> ]
1> c:\program files\microsoft visual studio 8\vc\include\set(69) : see reference to class template instantiation 'std::_Tree<_Traits>' being compiled
1> with
1> [
1> _Traits=std::_Tset_traits<data,std::less<data>,std::allocator<data>,false>
1> ]
1> c:\users\nitin_thokare\documents\visual studio 2005\projects\cpp\stl\ex_sets.cpp(31) : see reference to class template instantiation 'std::set<_Kty>' being compiled
1> with
1> [
1> _Kty=data
1> ]
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\string(151) : see declaration of 'std::operator <'
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const _Elem *,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const _Elem *' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\string(141) : see declaration of 'std::operator <'
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const std::basic_string<_Elem,_Traits,_Alloc> &)' : could not deduce template argument for 'const std::basic_string<_Elem,_Traits,_Alloc> &' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\string(131) : see declaration of 'std::operator <'
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\xutility(1880) : see declaration of 'std::operator <'
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const data'
1> c:\program files\microsoft visual studio 8\vc\include\utility(76) : see declaration of 'std::operator <'
1>c:\program files\microsoft visual studio 8\vc\include\functional(143) : error C2676: binary '<' : 'const data' does not define this operator or a conversion to a type acceptable to the predefined operator
答案 0 :(得分：1)
运算符＆lt; 未命中，它可以方便地编写为成员函数，如下所示，或者作为类外的友元操作符：
int geti() const;
bool operator<( data const& a2 ) const {
data const& a1 = *this;
return( a1.i < a2.i ||
(!(a1.i > a2.i) && (a1.f < a2.f)) ||
(!(a1.i > a2.i) && !(a1.f > a2.f) && (a1.c < a2.c)));
};
你也忘记了const限定符：
int geti() const;
答案 1 :(得分：1)
使用提供operator<作为已提及的另一个，或使用data作为std::set的第二个模板参数。
请参阅std::set声明：
template<
class Key,
class Compare = std::less<Key>,
class Allocator = std::allocator<Key>
> class set;
因此，您可以使用std::set<data,data>作为您的设置类型。这样，您的operator()将用于比较data个对象。
答案 2 :(得分：1)
使用Boost，因为我厌倦了样板。
class data {
...
public:
bool operator<(data const& other) const {
return boost::tie(this->i, this->f, this->c)
< boost::tie(other.i, other.f, other.c);
}
};
比你的版本更多，更可读。
答案 3 :(得分：0)
data类型没有<所需的比较运算符std::set。你可能想要
bool operator < ( data const& a2 ) const {
return( i < a2.i ||
(!(i > a2.i) && (f < a2.f)) ||
(!(i > a2.i) && !(f > a2.f) && (c < a2.c)));
}
而不是data::operator()。