我有一个 working iterator对于 MFC CObList - BaseMFCIter
。它适用于循环迭代,但我仍然无法使 ListIter
与 STL 算法 find_if 一起正常工作。
代码
#include < iterator >
#include "afxwin.h"
#include "afxtempl.h"
#include <iostream>
#include <algorithm>
#include <cstdlib>
class myCObject : public CObject
{
public:
myCObject( std::string val )
{
x = val;
}
std::string x;
};
template < typename Item, class Cont, class Key = POSITION >
class BaseMFCIter : public std::iterator < std::input_iterator_tag, Item >
{
public:
// Define types for the 2 member functions to be used:
typedef Key (Cont::*GetFirstFunctionPtr) () const;
typedef Item (Cont::*GetNextFunctionPtr) (Key&) const;
// Default constructor, makes a null iterator, equal to BaseMFCIter::end()
BaseMFCIter() : m_pCont(0), m_Pos(0), m_GetFirstFunc(0), m_GetNextFunc(0), m_End(true) {}
// Constructor taking pointer to container and the iteration functions
BaseMFCIter(Cont* pCont, GetFirstFunctionPtr pFF, GetNextFunctionPtr pNF)
: m_pCont(pCont), m_Pos(0), m_GetFirstFunc(pFF), m_GetNextFunc(pNF)
{ init(); }
// Copy constructor, initialises iterator to first element
BaseMFCIter(const BaseMFCIter& vi) : m_pCont(vi.m_pCont), m_Pos(0),
m_GetFirstFunc(vi.m_GetFirstFunc), m_GetNextFunc(vi.m_GetNextFunc)
{ init(); }
// Assignment operator, initialises iterator to first element
BaseMFCIter& operator=(const BaseMFCIter& vi)
{
m_pCont = vi.m_pCont;
m_GetFirstFunc = vi.m_GetFirstFunc;
m_GetNextFunc = vi.m_GetNextFunc;
init();
return *this;
}
bool operator == (const BaseMFCIter& rhs) const
{ return (m_Pos == rhs.m_Pos && m_End == rhs.m_End); }
bool operator != (const BaseMFCIter& rhs) const
{ return !operator==(rhs); }
BaseMFCIter& operator ++ () { advance(); return *this; }
BaseMFCIter& operator ++ (int) { BaseMFCIter ret(*this); advance(); return ret; }
Item operator * () { return m_Item; }
Item operator -> () { return m_Item; }
static BaseMFCIter end () { return BaseMFCIter(); } // end() returns default null iterator
private:
Item m_Item; // Current item from container
Cont* m_pCont; // Pointer to container
Key m_Pos; // Key to item in container
bool m_End; // Flag to indicate end of container reached
// Pointers to container iteration functions
GetFirstFunctionPtr m_GetFirstFunc;
GetNextFunctionPtr m_GetNextFunc;
// Use container GetFirst & GetNext functions to set to first element, or end() if not found
void init()
{
m_Pos = 0;
m_End = true;
if (m_pCont && m_GetFirstFunc != 0)
{
m_Pos = (m_pCont->*m_GetFirstFunc)();
advance();
}
}
// Use container GetNext function to find next element in container
void advance()
{
m_End = m_Pos ? false : true;
m_Item = (m_Pos && m_pCont && m_GetNextFunc != 0) ?
(m_pCont->*m_GetNextFunc)(m_Pos) : Item();
}
};
struct Container : public CObList
{
myCObject* GetNext(POSITION& rPosition)
{
return dynamic_cast<myCObject*>(CObList::GetNext(rPosition));
}
myCObject const* GetNext(POSITION& rPosition) const
{
return dynamic_cast<const myCObject*>(CObList::GetNext(rPosition));
}
};
class ListIter : public BaseMFCIter < const myCObject*, Container, POSITION >
{
public:
ListIter( Container* pObj = 0)
: BaseMFCIter< const myCObject*, Container, POSITION >
(pObj, &CObList::GetHeadPosition, &Container::GetNext)
{
}
};
struct Comparator
{
std::string stringToCompare;
bool operator() ( const myCObject* lhs )
{
return (bool) lhs->x.compare( stringToCompare );
}
};
void main( )
{
myCObject* m = new myCObject( "one" );
myCObject* n = new myCObject( "two" );
myCObject* p = new myCObject( "three" );
myCObject* q = new myCObject( "four" );
Container cont;
cont.AddHead( m );
cont.AddHead( n );
cont.AddHead( p );
cont.AddHead( q );
Comparator pred;
pred.stringToCompare = "1";
ListIter iter = ListIter( &cont );
ListIter endIter = ListIter( );
ListIter foundIter = std::find_if( iter, endIter, pred );
std::cout << "foundIter x is: " << foundIter->x.c_str() << std::endl;
}
给我 foundIter x is: four
。这可能是由于结束位置的定义方式而发生的
_InIt _Find_if(_InIt _First, _InIt _Last, _Pr _Pred)
{ // find first satisfying _Pred
_DEBUG_RANGE(_First, _Last);
_DEBUG_POINTER(_Pred);
for (; _First != _Last; ++_First)
if (_Pred(*_First))
break;
return (_First);
}
没有正确迭代,但我不知道如何修复它。
最佳答案
修复了一些问题:
(bool) lhs->x.compare( stringToCompare )
返回 true _whenever the string don't match** (seestring::compare
)- 您正在搜索不存在的“1”
- 由于谓词错误,您收到了第一个匹配项,即第一个元素,也插入了最后一个元素,名称为
"four"
:) - 您没有检查是否找到了有效的匹配项(取消引用结束迭代器是非法的,可能会使您的程序崩溃或做更糟糕的事情:未定义的行为)
- 你在输出语句中有一个多余的
x.c_str()
我将
Compare
谓词更改为更加地道:- 从构造函数中初始化
stringToCompare
- 使字段
const
- 使
operator()
成为const
方法
- 从构造函数中初始化
这应该可以解决问题(未经测试的代码,接下来的几个小时我不在编译器附近)
更新
到家后,我终于打开了调试器来跟踪那个奇怪的行为(见评论)。
令我沮丧的是,我发现 BaseMFCIter
是由对迭代器 是什么 的理解非常有限的人设计的:复制构造函数和赋值运算符完全错误:它们的效果是为同一个集合创建了一个新的 begin
迭代器。然而,这意味着迭代器永远不会从函数返回。
因此,我修复了它(首先通过正确实现它,然后通过删除现在冗余的构造函数和 operator= 以支持编译器生成的默认实现)。
查看 full history of my and your edits :
git clone git://gist.github.com/1353471.git
- sehe 11 分钟前依赖默认生成的复制构造函数和赋值
- sehe 12 分钟前修复了损坏的复制构造函数和赋值
- sehe 65 分钟前暂定
- Dmitry 73 分钟前尝试使用谓词查找 find_if
- sehe Heeren 25 小时前修复和测试 (VS2010)
- sehe 25 小时前 ( STL iterator for MFC container CObList )
#include "afxwin.h"
#include "afxtempl.h"
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <string>
#include <iterator>
class myCObject : public CObject
{
public:
myCObject( const std::string& val ) { x = val; }
std::string x;
};
template < typename Item, class Cont, class Key = POSITION >
class BaseMFCIter : public std::iterator < std::input_iterator_tag, Item >
{
public:
// Define types for the 2 member functions to be used:
typedef Key (Cont::*GetFirstFunctionPtr) () const;
typedef Item (Cont::*GetNextFunctionPtr) (Key&) const;
// Default constructor, makes a null iterator, equal to BaseMFCIter::end()
BaseMFCIter() : m_pCont(0), m_Pos(0), m_GetFirstFunc(0), m_GetNextFunc(0), m_End(true) {}
// Constructor taking pointer to container and the iteration functions
BaseMFCIter(Cont* pCont, GetFirstFunctionPtr pFF, GetNextFunctionPtr pNF)
: m_pCont(pCont), m_Pos(0), m_GetFirstFunc(pFF), m_GetNextFunc(pNF)
{ init(); }
bool operator == (const BaseMFCIter& rhs) const
{ return (m_Pos == rhs.m_Pos && m_End == rhs.m_End); }
bool operator != (const BaseMFCIter& rhs) const
{ return !operator==(rhs); }
BaseMFCIter& operator ++ () { advance(); return *this; }
BaseMFCIter& operator ++ (int) { BaseMFCIter ret(*this); advance(); return ret; }
Item operator * () { return m_Item; }
Item operator -> () { return m_Item; }
static BaseMFCIter end () { return BaseMFCIter(); } // end() returns default null iterator
private:
Item m_Item; // Current item from container
Cont* m_pCont; // Pointer to container
Key m_Pos; // Key to item in container
bool m_End; // Flag to indicate end of container reached
// Pointers to container iteration functions
GetFirstFunctionPtr m_GetFirstFunc;
GetNextFunctionPtr m_GetNextFunc;
// Use container GetFirst & GetNext functions to set to first element, or end() if not found
void init()
{
m_Pos = 0;
m_End = true;
if (m_pCont && m_GetFirstFunc != 0)
{
m_Pos = (m_pCont->*m_GetFirstFunc)();
advance();
}
}
// Use container GetNext function to find next element in container
void advance()
{
m_End = m_Pos ? false : true;
m_Item = (m_Pos && m_pCont && m_GetNextFunc != 0) ?
(m_pCont->*m_GetNextFunc)(m_Pos) : Item();
}
};
struct Container : public CObList
{
myCObject* GetNext(POSITION& rPosition)
{
return dynamic_cast<myCObject*>(CObList::GetNext(rPosition));
}
myCObject const* GetNext(POSITION& rPosition) const
{
return dynamic_cast<const myCObject*>(CObList::GetNext(rPosition));
}
};
class ListIter : public BaseMFCIter < const myCObject*, Container, POSITION >
{
public:
ListIter( Container* pObj = 0)
: BaseMFCIter< const myCObject*, Container, POSITION >
(pObj, &CObList::GetHeadPosition, &Container::GetNext)
{
}
};
struct Comparator
{
Comparator(const std::string& compareTo) : stringToCompare(compareTo) {}
bool operator() ( const myCObject* lhs ) const
{
return 0 == lhs->x.compare( stringToCompare );
}
private:
const std::string stringToCompare;
};
void main( )
{
myCObject* m = new myCObject( "one" );
myCObject* n = new myCObject( "two" );
myCObject* p = new myCObject( "three" );
myCObject* q = new myCObject( "four" );
Container cont;
cont.AddHead( m );
cont.AddHead( n );
cont.AddHead( p );
cont.AddHead( q );
Comparator pred("three");
ListIter iter = ListIter(&cont),
endIter = ListIter( );
ListIter foundIter = std::find_if( iter, endIter, pred );
if (endIter != foundIter)
{
std::cout << "foundIter x is: " << foundIter->x << std::endl;
}
else
{
std::cout << "not found" << std::endl;
}
}
关于collections - MFC 容器中的 find_if 具有从 std::iterator 派生的迭代器,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/8081735/