dat*_*ili 0 c++ compiler-errors using-directives overload-resolution name-lookup
#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
int square(int a){
return a*a;
}
struct Point{
int x,y;
};
int distance (const Point& a,const Point& b){
int k=(int) sqrt((float)((a.x-b.x)*(a.x-b.x))+((a.y-b.y)*(a.y-b.y)));
return k;
}
int main(){
vector<Point>a(10);
for (int i=0;i<10;i++){
cin>>a[i].x>>a[i].y;
}
int s=0;
int s1;
int k=0;
for (int i=1;i<10;i++){
s+=square(distance(a[0],a[i]));
}
for (int i=1;i<10;i++){
s1=0;
for (int j=0;j<10;j++){
s1+=square(distance(a[i],a[j]));
if (s1<s) { s=s1; k=i;}
}
}
cout<<k<<"Points are:";
cout<<a[k].x;
cout<<a[k].y;
return 0;
}
我有以下代码,但这里是错误列表
1>------ Build started: Project: distance, Configuration: Debug Win32 ------
1> distance.cpp
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(373): error C2039: 'iterator_category' : is not a member of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(9) : see declaration of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(30) : see reference to class template instantiation 'std::iterator_traits<_Iter>' being compiled
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(373): error C2146: syntax error : missing ';' before identifier 'iterator_category'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(373): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(373): error C2602: 'std::iterator_traits<_Iter>::iterator_category' is not a member of a base class of 'std::iterator_traits<_Iter>'
1> with
1> [
1> _Iter=Point
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(373) : see declaration of 'std::iterator_traits<_Iter>::iterator_category'
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(373): error C2868: 'std::iterator_traits<_Iter>::iterator_category' : illegal syntax for using-declaration; expected qualified-name
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(374): error C2039: 'value_type' : is not a member of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(9) : see declaration of 'Point'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(374): error C2146: syntax error : missing ';' before identifier 'value_type'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(374): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(374): error C2602: 'std::iterator_traits<_Iter>::value_type' is not a member of a base class of 'std::iterator_traits<_Iter>'
1> with
1> [
1> _Iter=Point
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(374) : see declaration of 'std::iterator_traits<_Iter>::value_type'
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(374): error C2868: 'std::iterator_traits<_Iter>::value_type' : illegal syntax for using-declaration; expected qualified-name
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(375): error C2039: 'difference_type' : is not a member of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(9) : see declaration of 'Point'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(375): error C2146: syntax error : missing ';' before identifier 'difference_type'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(375): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(375): error C2602: 'std::iterator_traits<_Iter>::difference_type' is not a member of a base class of 'std::iterator_traits<_Iter>'
1> with
1> [
1> _Iter=Point
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(375) : see declaration of 'std::iterator_traits<_Iter>::difference_type'
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(375): error C2868: 'std::iterator_traits<_Iter>::difference_type' : illegal syntax for using-declaration; expected qualified-name
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(377): error C2039: 'pointer' : is not a member of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(9) : see declaration of 'Point'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(377): error C2146: syntax error : missing ';' before identifier 'pointer'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(377): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(377): error C2602: 'std::iterator_traits<_Iter>::pointer' is not a member of a base class of 'std::iterator_traits<_Iter>'
1> with
1> [
1> _Iter=Point
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(377) : see declaration of 'std::iterator_traits<_Iter>::pointer'
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(377): error C2868: 'std::iterator_traits<_Iter>::pointer' : illegal syntax for using-declaration; expected qualified-name
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(378): error C2039: 'reference' : is not a member of 'Point'
1> d:\c++_algorithms\distance\distance\distance.cpp(9) : see declaration of 'Point'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(378): error C2146: syntax error : missing ';' before identifier 'reference'
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(378): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(378): error C2602: 'std::iterator_traits<_Iter>::reference' is not a member of a base class of 'std::iterator_traits<_Iter>'
1> with
1> [
1> _Iter=Point
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(378) : see declaration of 'std::iterator_traits<_Iter>::reference'
1> with
1> [
1> _Iter=Point
1> ]
1>c:\program files\microsoft visual studio 10.0\vc\include\xutility(378): error C2868: 'std::iterator_traits<_Iter>::reference' : illegal syntax for using-declaration; expected qualified-name
1> with
1> [
1> _Iter=Point
1> ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Jam*_*lis 26
这部分是由于您的使用造成的using namespace std;.
标准库中有一个函数,std::distance用于计算两个迭代器之间到容器的距离.在重载决策期间选择该功能而不是您的distance功能.
如果您不使用using namespace std;,则不会出现此问题.您的使用using namespace std;将std命名空间中的所有名称都带入全局命名空间.这很糟糕,因为在命名空间中有很多常用名称std,它可能会在名称查找过程中导致复杂的问题,正如您在此处发现的那样.
一般情况下,不要使用using namespace,尤其不要在文件范围内使用.从长远来看,要使用您想要使用的每个名称都要容易和清晰.
@James 是对的，摆脱using namespace std会让这个问题消失。但这并不完全是实际问题所在。
问题来自于 C++ 中名称的解析方式。如果没有找到合适的类成员，则在解析自由函数的名称时，C++ 使用非常激进的方法来解析名称查找。这称为参数相关名称查找（或 ADL），有时称为 Koenig 查找。同时，它也是 C++ 如此强大，但也如此致命和令人困惑的原因之一。
这是基本问题，经过简化。
您调用vector::operator[]它返回 avector::reference或 a vector::const_reference。您获取此返回值并调用distance()unqualified。
因为distance在适用的类中找不到，所以 ADL 启动，它会出去并获取太多潜在的匹配名称。
然后，ADL 会仔细检查候选者列表并选择“最佳匹配”。在这种情况下，返回reference的比您的operator[]期望的类型更匹配，尽管两者兼容，因此被选中。std::distancedistancestd::distance
解决这个问题的几种方法：
using namespace std。相反，using只有您想要的部分。distance使用范围解析运算符明确量化您所引用的内容：::distance()distance为采用指针而不是const &. 这有效地关闭了 ADL： 例子：
int distance(const Point* a,const Point* b)
s+=square(distance(&a[0],&a[1]));
其他资源：
“一个温和的建议：修复 ADL（修订版 2）”作者：Herb Sutter