C++ 如何在地图中存储指针
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how to store pointers in map
提问by Venkata
I am working on one of the project which requires
我正在从事需要的项目之一
class MyObj;
map<string, MyObj*> myMap;
Here logic is here to map file name to MyObj class.
这里的逻辑是将文件名映射到 MyObj 类。
If I try to insert following
如果我尝试插入以下内容
string strFilename = "MyFile";
MyObj* pObj = new MyObj();
myMap.insert(strFileName, pObj); // This line throwing following error.
no matching function for call to
'std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, void*, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, void*> > >::insert(std::string&, void*)'
没有匹配的函数调用
'std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, void*, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, void*> > >::insert(std::string&, void*)'
Can any one please help me how to solve this. Are is there better way we can do this using STL
任何人都可以帮助我如何解决这个问题。有没有更好的方法可以使用 STL 做到这一点
回答by Moo-Juice
I've typedef'd this stuff to make it more readable...
我已经对这些东西进行了 typedef 以使其更具可读性...
typedef std::map<std::string, MyObj*> MyMap;
typedef std::pair<std::string, MyObj*> MyPair;
MyMap myMap;
string strFilename = "MyFile";
MyObj* pObj = new MyObj();
myMap.insert(MyPair(strFilename, pObj));
回答by robev
std::map requires a pair when you use the insert function.
使用插入函数时， std::map 需要一对。
You have two options, either:
您有两种选择：
myMap[strFileName] = pObj;
Or:
或者：
myMap.insert(std::make_pair(strFileName,pObj));
回答by Prasoon Saurav
myMap.insert(strFileName, pObj);
myMap.insert(strFileName, pObj);
Use make_pair()inside insert()
make_pair()内部使用insert()
#include <utility>
//...
myMap.insert (std::make_pair(strFileName, pObj) ) ;
回答by Steve M
There is no insertmember that takes a key and a value as arguments. Just use the index operator:
没有insert将键和值作为参数的成员。只需使用索引运算符：
myMap[fileName] = obj;
回答by Strahd_za
map<string,MyObj*> myMap;
string strFilename = "MyFile";
MyObj* pObj = new MyObj();
myMap[strFilename] = pObj;
Should work just fine. Just remember clearing the map wont free up the memory the pointers are pointing to.
应该工作得很好。请记住清除地图不会释放指针指向的内存。
回答by Paul Rubel
Insert wants a pair, try something like this:
插入想要一对，试试这样的：
mymap.insert ( pair<string,MyObj*>(strFilename,pObj) );
回答by Denis Shevchenko
Try boost::ptr_map (from boost::ptr_container library). And with boost::assign library you even do not need to call new manually:
尝试 boost::ptr_map （来自 boost::ptr_container 库）。使用 boost::assign 库，您甚至不需要手动调用 new ：
class MyObj {
MyObj() { /* some... */ }
};
typedef boost::ptr_map< string, MyObj > MyMap;
MyMap m;
using namespace boost::assign;
ptr_map_insert( m )( "first" )( "second" )( "third" );
In this case three elements will added in m (with keys "first", "second" and "third" and with three created objects MyObj()).
在这种情况下，三个元素将添加到 m（带有键“first”、“second”和“third”以及三个创建的对象 MyObj()）。
Or:
或者：
class MyObj {
MyObj( int _i ) : i( _i ) { /* some... */ }
int i;
};
typedef boost::ptr_map< string, MyObj > MyMap;
MyMap m;
using namespace boost::assign;
ptr_map_insert( m )( "first", 1 )( "second", 2 )( "third", 3 );
In this case three elements will added in m. First element have key "first" and value MyObj( 1 ), second - key "second" and MyObj( 2 ), third - key "third" and MyObj( 3 ).
在这种情况下，三个元素将添加到 m 中。第一个元素具有键“first”和值 MyObj(1)，第二个键是“second”和 MyObj(2)，第三个键是“third”和 MyObj(3)。
回答by Denis Shevchenko
Try boost::ptr_map ()
试试 boost::ptr_map()
回答by Dima
You are calling insert()incorrectly. It does not take a key and a value separately, it takes a pair like this:
你调用insert()错误。它不需要单独的键和值，它需要一对像这样：
myMap.insert(pair < string, MyObj* > (strFileName, pObj));
