Instructions and tips for using map containers in C + +

The map container in C + + provides a key-value pair container, and the difference between map and Multimap is only that multiple allows a key to correspond to multiple values.

I. Description of MAP
1 Header Files
#include <map>

2 Definitions
Map<string, int> My_map;
or a typedef map<string, int> My_map;
My_map My_map;

3 Inserting data
(1) my_map["a"] = 1;
(2) My_map.insert (map<string, Int>::value_type ("B", 2));
(3) My_map.insert (pair<string,int> ("C", 3));
(4) My_map.insert (make_pair<string,int> ("D", 4));

4 finding data and modifying data
(1) int i = my_map["a"];
My_map["a"] = i;
(2) My_map::iterator My_itr;
My_itr.find ("B");
Int J = my_itr->second;
My_itr->second = j;
Note, however, that the key itself cannot be modified unless it is deleted.

5 Deleting data
(1) my_map.erase (MY_ITR);
(2) My_map.erase ("C");
It is also important to note that the first case cannot be deleted during the iteration, just as the element cannot be deleted while foreach.

6 Iterative data
For (My_itr=my_map.begin ();   My_itr!=my_map.end (); ++MY_ITR) {}

7 Other methods
My_map.size () returns the number of elements
My_map.empty () to determine if it is empty
My_map.clear () clears all elements
can be assigned and compared directly: =, >=, &lt, <=,! =, etc.

More advanced application Check help go, ^_^;

Examples of two/map

Requirements: Delete items with a greater than 100 of itemstruct in Mymap
struct ITEMSTRUCT
{
int A;
Char b[20];
};
Map<string, Itemstruct > Mymap.

Answer 1:
#include <iostream>
#include <ctime>
#include <map>
using namespace Std;
typedef struct ITEMSTRUCT
{
int A;
Char b[20];
}items;
ItemS S[4] = {{102, "what"},
{, "Hello"},
{198, "world"},
{"C + +"}
};;


int main ()
{
Map<string, items> Mymap;
String Str[4] = {"1st", "2nd", "3rd", "4th"};
for (int i = 0;   i<4; i++)
{
Mymap.insert (Make_pair (Str[i], s[i]));
}

Map<string,items>::iterator it;
For (It=mymap.begin (); It!=mymap.end (); it++)
{
if (it->second.a >100) {
I=mymap.erase (IT); -----> Correct
Mymap.erase (IT); ----->it failure.
}
}
First is key, second is value;
for (it = Mymap.begin (); It!=mymap.end (); it++)
{
cout<<it->first<< "" <<it->second.a<< "" <<it->second.b<<endl;
}
System ("pause");
return 0;
}

Answer 2:
#include <map>
#include <iterator>
#include <string>
#include <iostream>
#include <cstring>
using namespace Std;
struct ITEMSTRUCT
{
int A;
Char b[20];
itemstruct (int t,char*str)
{
a=t;
strcpy (B,STR);
}
};
int main ()
{
map<string,itemstruct>mymap;
Mymap.insert (Make_pair ("A", Itemstruct (Ten, "Hanzhou"));
Mymap.insert (Make_pair ("AB", Itemstruct ("Fuzhou")));
Mymap.insert (Make_pair ("abc", Itemstruct ("Zhengzhou")));
Mymap.insert (Make_pair ("ABCD", Itemstruct ("Wuhan")));
Mymap.insert (Make_pair ("ABCDE", Itemstruct ("Kunming")));
Mymap.insert (Make_pair ("ABCdef", Itemstruct ("Xiamen")));
Map<string,itemstruct>::iterator It=mymap.begin ();
while (It!=mymap.end ())
{
if ((It->second). a>100) Mymap.erase (it++);
else it++;
}
It=mymap.begin ();
while (It!=mymap.end ())
{
cout<<it->first<< "" << (It->second) .a<< "" << (It->second) .b<<endl;
it++;
}
System ("PAUSE");
return 0;
}

Answer 3:
  for (map<string,   itemstruct>::iterator   i    =   mymap.begin ();   i   !=    Mymap.end ();)  
  { 
          if ( i->second.a   >   100)  
                   i   =    Mymap.erase (i);  
          else 
                   ++i;  
  } 

Solution to compile error in compiling map in 4:VC6
Warnings similar to the following is generated even if you use the warning pragma to disable the warning:warning C4786: ' Std::rb_tree<caispanningtree<state,std::less<state>>::transclosurenode, CAiSpanningTree< State,std::less<state>>::transclosurenode,std::ident<cai spanningtree<state,std::less<state >>::transclosurenode,caispanningtree<s tate,std::less<state>>::transclosurenode>,std::less <caispanningtree<stat e,std::less<state>>::transclosurenode>> ': identifier was truncated to ' 255 ' characters in the debug information

Fix code added to the stdafx.h header file:

#pragma warning (disable:4786)

Http://www.cnblogs.com/anywei/archive/2011/10/27/2226830.html

Instructions and tips for using map containers in C + +