Материал из C\C++ эксперт
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;
}
