C++ Tutorial/map multimap/map find — различия между версиями

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Текущая версия на 10:28, 25 мая 2010

Find value by key

#include <map>
#include <iostream>
#include <string>
using namespace std;
typedef map<int, string> INT2STRING;
int main(void){
   INT2STRING theMap;
   INT2STRING::iterator theIterator;
   string theString = "One, Two";
   int index= 1;
   theMap.insert(INT2STRING::value_type(0,"Zero"));
   theMap.insert(INT2STRING::value_type(1,"One"));
   theMap.insert(INT2STRING::value_type(2,"Two"));
   theMap.insert(INT2STRING::value_type(3,"Three"));
   theMap.insert(INT2STRING::value_type(4,"Four"));
   theMap.insert(INT2STRING::value_type(5,"Five"));
   theMap.insert(INT2STRING::value_type(6,"Six"));
   theMap.insert(INT2STRING::value_type(7,"Seven"));
   theMap.insert(INT2STRING::value_type(8,"Eight"));
   theMap.insert(INT2STRING::value_type(9,"Nine"));

   for( index = 0; index < theString.length(); index++){
      theIterator = theMap.find(theString[index] - "0");
      if(theIterator != theMap.end())      // is 0 - 9
        cout << (*theIterator).second << " ";
      else                // not 0 - 9
        cout << "[err] ";
   }
 }

Map find demo

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;
/* function object to check the value of a map element
 */
template <class K, class V>
class value_equals {
  private:
    V value;
  public:
    // constructor (initialize value to compare with)
    value_equals (const V& v)
     : value(v) {
    }
    // comparison
    bool operator() (pair<const K, V> elem) {
        return elem.second == value;
    }
};
int main()
{
    typedef map<float,float> FloatFloatMap;
    FloatFloatMap coll;
    FloatFloatMap::iterator pos;
    // fill container
    coll[1]=7;
    coll[2]=4;
    coll[3]=2;
    coll[4]=3;
    coll[5]=6;
    coll[6]=1;
    coll[7]=3;
    // search an element with key 3.0
    pos = coll.find(3.0);                     // logarithmic complexity
    if (pos != coll.end()) {
        cout << pos->first << ": "
             << pos->second << endl;
    }
}
3: 2

map: find_if

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */
#include <iostream>
#include <algorithm>
#include <map>
using namespace std;
/* function object to check the value of a map element
 */
template <class K, class V>
class value_equals {
  private:
    V value;
  public:
    // constructor (initialize value to compare with)
    value_equals (const V& v)
     : value(v) {
    }
    // comparison
    bool operator() (pair<const K, V> elem) {
        return elem.second == value;
    }
};
int main()
{
    typedef map<float,float> FloatFloatMap;
    FloatFloatMap coll;
    FloatFloatMap::iterator pos;
    // fill container
    coll[1]=7;
    coll[2]=4;
    coll[3]=2;
    coll[4]=3;
    coll[5]=6;
    coll[6]=1;
    coll[7]=3;
    // search an element with value 3.0
    pos = find_if(coll.begin(),coll.end(),    // linear complexity
                  value_equals<float,float>(3.0));
    if (pos != coll.end()) {
        cout << pos->first << ": "
             << pos->second << endl;
    }
}
4: 3

Use find() to find an entry in a map

#include <iostream>
#include <string>
#include <map>
#include <utility>
using namespace std;
void show(const char *msg, map<string, string> mp);
int main() {
  map<string, string> phonemap;
  phonemap["A"] = "444-555-1234";
  phonemap["B"] = "555-555-6576";
  phonemap["C"] = "555-555-9843";
  show("Here is the original map: ", phonemap);
  phonemap["B"] = "555 555-5555";
  cout << "New number: " << phonemap["B"] << endl;
  // Use find() to find a number.
  map<string, string>::iterator itr;
  itr = phonemap.find("B");
  if(itr != phonemap.end())
    cout << "Number is " << itr->second << endl;
  return 0;
}
// Display the contents of a map<string, string> by using an iterator.
void show(const char *msg, map<string, string> mp) {
  map<string, string>::iterator itr;
  cout << msg << endl;
  for(itr=mp.begin(); itr != mp.end(); ++itr)
   cout << " " << itr->first << ": " << itr->second << endl;
  cout << endl;
}
Источник — «http://cppe.ru/index.php?title=C%2B%2B_Tutorial/map_multimap/map_find&oldid=2074»