c++ - std::set.insert 不会与自定义类一起编译

Question

这个问题已经有答案了:

problems with c++ set container (2 个回答)

已关闭 10 年前。

我有一个类 Record，它具有三个私有(private)整数字段、getter 和 setter，以及一个默认的特定构造函数。我打算用记录填充一组，但在使代码正常工作时遇到问题。

#include <set>
using namespace std;

class Record
{
    int a, b, c;
    public:
    //getters and setters
    Record(){a = -1; b = -1; c = -1;};
}

int main()
{
    set< Record > s;
    s.insert(Record());
}

尝试编译会导致此错误:

C:\Users\Denton\Documents\Indiana University\Class Documents\Spring 2013\CSCI-H2 12\Assignment9>g++ a9.cpp -o a9 In file included from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/string:5 0:0, from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/loc ale_classes.h:42, from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/ios _base.h:43, from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/ios:43, from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/ostream: 40, from c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/iostream :40, from a9.cpp:3: c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_function.h: In member function 'bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _ Tp = Record]': c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:1267:4: inst antiated from 'std::pair, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(const _Val&) [with _Key = Record, _Val = Record, _KeyOfValue = std::_Identity, _Compare = std::l ess, _Alloc = std::allocator]' c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_set.h:410:29: insta ntiated from 'std::pair, _Compare, typename _Alloc::rebind<_Key>::other>::const_iterator, bool> std::set <_Key, _Compare, _Alloc>::insert(const value_type&) [with _Key = Record, _Compar e = std::less, _Alloc = std::allocator, typename std::_Rb_tree<_ Key, _Key, std::_Identity<_Key>, _Compare, typename _Alloc::rebind<_Key>::other> ::const_iterator = std::_Rb_tree_const_iterator, std::set<_Key, _Compare , _Alloc>::value_type = Record]' a9.cpp:72:28: instantiated from here c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_function.h:236:22: er ror: no match for 'operator<' in '__x < __y' c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_function.h:236:22: no te: candidates are: c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_pair.h:207:5: note: t emplate bool std::operator<(const std::pair<_T1, _T2>&, co nst std::pair<_T1, _T2>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:291:5: not e: template bool std::operator<(const std::reverse_iterator<_It erator>&, const std::reverse_iterator<_Iterator>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_iterator.h:341:5: not e: template bool std::operator<(const std::r everse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2510:5: no te: template bool std::operator<(cons t std::basic_string<_CharT, _Traits, _Alloc>&, const std::basic_string<_CharT, _ Traits, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2522:5: no te: template bool std::operator<(cons t std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/basic_string.h:2534:5: no te: template bool std::operator<(cons t _CharT*, const std::basic_string<_CharT, _Traits, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_vector.h:1290:5: note : template bool std::operator<(const std::vector<_Tp, _ Alloc>&, const std::vector<_Tp, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_list.h:1593:5: note: template bool std::operator<(const std::list<_Tp, _Allo c>&, const std::list<_Tp, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_tree.h:856:5: note: t emplate bool std::operator<(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _All oc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_set.h:713:5: note: te mplate bool std::operator<(const std:: set<_Key, _Compare, _Alloc>&, const std::set<_Key, _Compare, _Alloc>&) c:\mingw\bin../lib/gcc/mingw32/4.6.2/include/c++/bits/stl_multiset.h:696:5: not e: template bool std::operator<(const std::multiset<_Key, _Compare, _Alloc>&, const std::multiset<_Key, _Compare, _All oc>&)

当我制作一组 s 和 s.insert(1) 时，插入工作正常需要做什么才能编译此代码？

提前致谢。

Answer 1

您需要重载 operator< :像下面这样:

bool operator<(const Record& rhs) const 
{
   return a < rhs.a;  //assume that you compare the record based on a
}

原因是STL集合维护元素的顺序。 std::set 支持指定比较函数。默认为less这将使用 operator <检查相等性。

同时，您必须以 ; 结束类定义。否则编译错误。

class Record
{
   int a, b, c;
   public:
   //getters and setters
   Record(){a = -1; b = -1; c = -1;};
}; //<---Cannot miss this ;