好的......我有这个结构和比较功能 -
struct Edge
{
char point1;
char point2;
int weight;
bool operator<( const Edge& rhs ) const
{
return( weight < rhs.weight );
}
}; //end Edge
bool compareEdge( const Edge& lhs, const Edge& rhs )
{
return( lhs.weight < rhs.weight );
}
我有一个声明为...的向量
vector<Edge> edges;
最后，我尝试使用＆lt;操作者...
sort( edges.begin(), edges.end() );
我在Visual Studio 2005中遇到以下错误......
------ Build started: Project: RadakovichLab6, Configuration: Debug Win32 ------ Compiling... graph.cpp c:\program files\microsoft visual studio 8\vc\include\algorithm(2981) : error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const Edge' (or there is no acceptable conversion)
c:\documents and settings\jake\my documents\visual studio 2005\projects\radakovichlab6\graph.h(25): could be 'Edge &Edge::operator =(const Edge &)'
while trying to match the argument list '(const Edge, Edge)'
c:\program files\microsoft visual studio 8\vc\include\algorithm(2997) : see reference to function template instantiation 'void std::_Insertion_sort1<_BidIt,Edge>(_BidIt,_BidIt,_Ty*)' being compiled
with
[
_BidIt=std::_Vector_const_iterator<Edge,std::allocator<Edge>>,
_Ty=Edge
]
c:\program files\microsoft visual studio 8\vc\include\algorithm(3105) : see reference to function template instantiation 'void std::_Insertion_sort<_RanIt>(_BidIt,_BidIt)' being compiled
with
[
_RanIt=std::_Vector_const_iterator<Edge,std::allocator<Edge>>,
_BidIt=std::_Vector_const_iterator<Edge,std::allocator<Edge>>
]
c:\program files\microsoft visual studio 8\vc\include\algorithm(3112) : see reference to function template instantiation 'void std::_Sort<std::_Vector_const_iterator<_Ty,_Alloc>,__w64 int>(_RanIt,_RanIt,_Diff)' being compiled
with
[
_Ty=Edge,
_Alloc=std::allocator<Edge>,
_RanIt=std::_Vector_const_iterator<Edge,std::allocator<Edge>>,
_Diff=__w64 int
]
c:\documents and settings\jake\my documents\visual studio 2005\projects\radakovichlab6\graph.cpp(107) : see reference to function template instantiation 'void std::sort<std::_Vector_const_iterator<_Ty,_Alloc>>(_RanIt,_RanIt)' being compiled
with
[
_Ty=Edge,
_Alloc=std::allocator<Edge>,
_RanIt=std::_Vector_const_iterator<Edge,std::allocator<Edge>>
] c:\program files\microsoft visual studio 8\vc\include\algorithm(2988) : error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const Edge' (or there is no acceptable conversion)
c:\documents and settings\jake\my documents\visual studio 2005\projects\radakovichlab6\graph.h(25): could be 'Edge &Edge::operator =(const Edge &)'
while trying to match the argument list '(const Edge, const Edge)' c:\program files\microsoft visual studio 8\vc\include\algorithm(2989) : error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const Edge' (or there is no acceptable conversion)
c:\documents and settings\jake\my documents\visual studio 2005\projects\radakovichlab6\graph.h(25): could be 'Edge &Edge::operator =(const Edge &)'
while trying to match the argument list '(const Edge, Edge)' Generating Code... Compiling... main.cpp Generating Code... Build log was saved at "file://c:\Documents and Settings\Jake\My Documents\Visual Studio 2005\Projects\RadakovichLab6\Debug\BuildLog.htm" RadakovichLab6 - 3 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
问题出在错误的第一行。我是否使用重载＆lt;运算符，或将比较函数传递给std :: sort函数。我想，Edge结构的默认赋值运算符应该足够了，因为没有动态分配的内存。如果有人有任何见解，我将不胜感激。
完整代码......
#include <list>
#include <map>
#include <queue>
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;
//the Edge and aGraph together represent the adjacency list
//representation of a graph.
struct Edge
{
char point1; //this represents the endpoint of an edge
char point2;
int weight; //this is the weight of the edge
bool operator<( const Edge& rhs ) const
{
return( weight < rhs.weight );
}
}; //end Edge
class Graph
{
public:
//Default constructor
Graph();
//This method inputs an edge into a graph.
void inputEdge( char pointA, char pointB, int wt )
{
//used to input the edges of the graph
Edge anEdge;
//prepare for insertion into list
anEdge.point1 = pointA;
anEdge.point2 = pointB;
anEdge.weight = wt;
edges.push_back( anEdge );
//insert edge into the adjacency list.
aGraph[pointA].push_front( pointB );
//insert the opposite direction into the
//adjacency list.
aGraph[pointB].push_front( pointA )
}
//This...
void bfs();
//This prints a graph and is used only for debugging purposes.
void printGraph() const
{
list<char>::const_iterator listIter;
map<char, list<char>>::const_iterator mapIter;
for( mapIter = aGraph.begin();
mapIter != aGraph.end();
mapIter++ )
{
for( listIter = mapIter->second.begin();
listIter != mapIter->second.end();
listIter++ )
{
cout << mapIter->first << " " << *listIter << endl;
} //end for
} //end for
sort( edges.begin(), edges.end() );
vector<Edge>::const_iterator vectIt;
for( vectIt = edges.begin();
vectIt != edges.end();
vectIt++ )
{
cout << vectIt->point1 << " " << vectIt->point2 << " " << vectIt->weight << endl;
} //end for
} //end printGraph
private:
//This is the adjacency list
map<char, list<char>> aGraph;
//This is a list of edges and their weights.
vector<Edge> edges;
}; //end Graph
int main()
{
Graph myGraph;
myGraph.inputEdge( 'O', 'A', 2 );
myGraph.inputEdge( 'O', 'B', 5 );
myGraph.inputEdge( 'O', 'C', 4 );
myGraph.inputEdge( 'A', 'B', 2 );
myGraph.inputEdge( 'A', 'D', 7 );
myGraph.inputEdge( 'B', 'D', 4 );
myGraph.inputEdge( 'B', 'E', 3 );
myGraph.inputEdge( 'C', 'B', 1 );
myGraph.inputEdge( 'C', 'E', 4 );
myGraph.inputEdge( 'E', 'D', 1 );
myGraph.inputEdge( 'D', 'T', 5 );
myGraph.inputEdge( 'E', 'T', 7 );
myGraph.inputEdge( 'G', 'Z', 8 );
myGraph.printGraph();
cout << endl << endl;
system("PAUSE");
return 0;
} //end main
这是代码......
答案 0 :(得分：4)
您正在使用无法排序的const vector。 （或改变了。）
这是因为您的功能是const：
void printGraph() const
删除const，以便修改（并因此排序）类的成员。
答案 1 :(得分：3)
以下代码在g ++ 4.4.0下编译：
#include <algorithm>
#include <vector>
using namespace std;
struct Edge {
char point1;
char point2;
int weight;
bool operator<( const Edge& rhs ) const {
return( weight < rhs.weight );
}
};
bool compareEdge( const Edge& lhs, const Edge& rhs ) {
return( lhs.weight < rhs.weight );
}
int main() {
vector <Edge> edges;
sort( edges.begin(), edges.end() );
}
请使用您的编译器进行测试。一般来说，如果你和其他人发布了这样的小型完整程序，这些程序可以很容易地进行测试，并且说明问题（或者在这种情况下缺少它们），那将会很有帮助。
答案 2 :(得分：0)
上面的代码编译得很好，在尝试将内容分配给const Edge时，看起来你有一个赋值问题。
您不需要定义赋值运算符，但不能将某些内容赋给const Edge。
答案 3 :(得分：0)
我认为您使用std::sort而不是std::vector<Edge>::const_iterator拨打std::vector<Edge>::iterator，可能在graph.cpp第107行。
看到代码之后：迭代器确实是不变的。 edges是Graph的成员变量，printGraph是const方法。因此，无法在edges内修改printGraph，因为const方法无法修改Graph对象。排序edges会对其进行修改，因此会导致编译错误。
答案 4 :(得分：0)
printGraph函数被声明为Graph的const成员函数，但您正在尝试修改成员变量（edge vector）。从printGraph声明中删除const，代码将编译。
或者制作边缘矢量的局部副本并在打印之前对其进行排序，因为注释状态此功能仅用于调试性能不应该是主要关注点。对于一个名为printGraph的函数来说，无论如何都要修改边缘向量，这有点误导。