返回信息流可以进行插入，我用迭代器看实现了我想要的排序，但是在查找的时候编译出问题，现实 不能将 const compare 转化为 compare &，请问何解？
程序类似这样
struct point
{
double priority；
int UUID；
point(int _UUID,double priority):UUID(_UUID),priority(_priority)
{}
};
struct compare
{
bool operator()(point * p1,point *p2)
{
if(p1->priority<p2->priority) return true;
if(p1->priority==p2->priority)
{
if(p1->UUID<p2->UUID)
return true;
}
return false;
}
};
void main()
{
set<point*,compare> Set;
point * p,*p1;
for(int i==0;i<10;++i)
{
p=new point(i,(rand()%10)/10.0 );
Set.insert(p);
if(i==5) p1=p;
}
set<point*,compare>::iterator iter=Set.begin();
//排序没有问题
while(iter!=Set.end())
{
cout<<(*iter)->priority<<" "<<(*iter)->UUID<<endl;
++iter;
}
//查找编译出错
Set.find(p1);
}
求解啊，现在能想到的就是用map<point,point*>，但这样空间太大啊。
这是一条镜像帖。来源：北邮人论坛 / cpp / #85954同步于 2015/3/15
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CPP机器人发帖
[问题]set中保存自建类型的指针怎么实现不了find()？
liufangyu247
2015/3/15镜像同步12 回复
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9 条回复
【 在 inaadversity 的大作中提到: 】
: 没有错啊 把出错信息贴出来看看
没有错吗？我这个程序我在vc6上会编出错，没有find()那句可以，有了就会出错，我去实验室再上图。
楼主试试C++11的lambda表达式？
#include <iostream>
#include <algorithm>
#include <cstdlib>
using namespace std;
int ar[] = {-9,-7,-5,-3,-1,0,2,4,6,8};
int main()
{
sort(ar, ar+10, [](int a, int b){return abs(a)<abs(b);});
for(auto i : ar) {
cout<<i<<endl;
}
return 0;
}
【 在 nuanyangyang 的大作中提到: 】
: 楼主试试C++11的lambda表达式？
: [code=cpp]
: #include <iostream>
: ...................
只能用vc6……
【 在 inaadversity 的大作中提到: 】
: 没有错啊 把出错信息贴出来看看
#include<iostream>
#include<set>
using namespace std;
struct CTracePoint
{
CTracePoint(int _UID,double _priority=0.0):
UID(_UID),priority(_priority)
{
}
int UID;
double x;
double y;
double priority;
};
ostream & operator<<(ostream &os,CTracePoint *p)
{
os
<<" "<<"priority:"<<p->priority
<<" "<<"UID:"<<p->UID
<<" "<<"ADDRESS:"<<(void *)p
// <<" "<<"x:"<<p->x
// <<" "<<"y:"<<p->y
;
return os;
}
struct compare
{
bool operator()(CTracePoint * val1,CTracePoint *val2)
{
if (val1->priority<val2->priority)
{
return true;
}
if (val1->priority==val2->priority)
{
if (val1->UID<val2->UID)
{
return true;
}
}
return false;
}
};
//主程序这样，输出没问题
void main(int argc,char *argv[])
{
set<CTracePoint *,compare> Set;
static int UID=0;
srand(NULL);
CTracePoint *search;
for (int i=0;i<20;++i)
{
CTracePoint *p=new CTracePoint(UID++,(rand()%10)/10.0);
Set.insert(p);
if(i==0) search=p;
}
set<CTracePoint *,compare>::iterator iter=Set.begin();
while (iter!=Set.end())
{
cout<<*iter++<<endl;
}
//加这段显示错误：
Set.find(search);
/*
d:\program files\microsoft visual studio\vc98\include\xtree(514) : error C2662: '()' : cannot convert 'this' pointer from 'const struct compare' to 'struct compare &'
Conversion loses qualifiers
d:\program files\microsoft visual studio\vc98\include\xtree(511) : while compiling class-template member function 'struct std::_Tree<struct CTracePoint
*,struct CTracePoint *,struct std::set<struct CTracePoint *,struct compare,class std::allocator<struct CTracePoint *> >::_Kfn,struct compare,class
std::allocator<struct CTracePoint *> >::_Node *__thiscall std::_Tree<struct CTracePoint *,struct CTracePoint *,struct std::set<struct CTracePoint *,struct
compare,class std::allocator<struct CTracePoint *> >::_Kfn,struct compare,class std::allocator<struct CTracePoint *> >::_Lbound(struct CTracePoint *const & ) const'
d:\program files\microsoft visual studio\vc98\include\xtree(514) : error C2064: term does not evaluate to a function
d:\program files\microsoft visual studio\vc98\include\xtree(511) : while compiling class-template member function 'struct std::_Tree<struct CTracePoint
*,struct CTracePoint *,struct std::set<struct CTracePoint *,struct compare,class std::allocator<struct CTracePoint *> >::_Kfn,struct compare,class
std::allocator<struct CTracePoint *> >::_Node *__thiscall std::_Tree<struct CTracePoint *,struct CTracePoint *,struct std::set<struct CTracePoint *,struct
compare,class std::allocator<struct CTracePoint *> >::_Kfn,struct compare,class std::allocator<struct CTracePoint *> >::_Lbound(struct CTracePoint *const & ) const'
*/
}
我测试了下，比如：
void main(int argc,char *argv[])
{
set<CTracePoint *,compare> Set;
static int UID=0;
srand(NULL);
CTracePoint *search;
for (int i=0;i<20;++i)
{
CTracePoint *p=new CTracePoint(UID++,(rand()%10)/10.0);
Set.insert(p);
if(i==5) search=p;
}
cout<<"size:"<<Set.size()<<endl;
Set.insert(new CTracePoint(search->UID,search->priority));
cout<<"size:"<<Set.size()<<endl;
set<CTracePoint *,compare>::iterator iter=Set.begin();
while (iter!=Set.end())
{
cout<<*iter++<<endl;
}
}
测试显示size没有变化，说明是可以检测相同的值的，虽然指针不同（但是实际中实现的时候可以保证UID的唯一性），那我就想问为什么find（） count（）都不可以实现呢？