Instructions 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.h>

2. Defining methods

(1) map<string,int> m;

(2) typedef map<string,int> M;

M m;

3. Inserting data

(1) m[' a '] = 1

(2) M.insert (Map<string,int>::value_type ("B", 2));

(3) M.insert (pair<string,int> ("C", 3));

(4) M.insert (make_pair<string,int> ("D", 4));

4. Finding data and modifying data

(1) int i = m["a"];

M["a"] = i;

(2) M::iterator m_iter;

M.find ("B");

Int J = m_iter->second;

M_iter->second = j;

!!! NOTE!!! The key itself cannot be modified unless it is deleted.

5. Delete data

(1) m.erase (m_iter);

(2) M.erase ("C");

!!! Attention!!! The first case cannot be deleted during the iteration

6 Iterative data
For (M_iter=m.begin ();   M_iter!=m.end (); ++m_iter)

{

}

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

Examples of two maps

<span style= "FONT-SIZE:18PX;" > Requirements: Remove the  struct itemstruct {      int a) from the item itemstruct a greater than 100 in Mymap;      Char b[20]; }; Map<string,itemstruct> mymap;</span>

Code Listing 1:

<span style= "FONT-SIZE:18PX;" > #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 and second is value;  for (it = Mymap.begin (); It!=mymap.end (); it++) {cout<<it->first<< "" <<it->second.a<< "" <<it->second.b<<en     dl     } system ("Pause");  Return 0; }</span>

Code Listing 2:

<span style= "FONT-SIZE:18PX;" > #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; }</span>

Code Listing 3:

<span style= "FONT-SIZE:18PX;" >for (map<string,   itemstruct>::iterator   i   =   mymap.begin ();   I!   =   mymap.end ();) {     if (i->second.a   >   )        i   =   mymap.erase (i);     else        ++i;} </span>

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Instructions for using map containers in C + +