Maps and the Sort Algorithm
Here are a number of example programs that use the Map STL class and the
STL sort algorithm.
map example
Here is a map example in which several employees are inserted into the map
by name and then
an employee named "nels" is found and his age is printed:
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#include <iostream>
#include <string>
#include <map>
using namespace std;
class employee {
public:
int age;
string name;
employee(int emp_age, string emp_name) :
age(emp_age), name(emp_name) {}
};
main() {
map<string, employee *> employee_table;
employee_table.insert(make_pair("brad", new employee(43, "brad")));
employee_table.insert(make_pair("nels", new employee(42, "nels")));
employee_table.insert(make_pair("james", new employee(76, "james")));
// insert returns a pair object whose elements are:
// 1) an iterator that points to the inserted element, if the insertion
// succeeded, and
// 2) a bool that indicates whether or not the insertion succeeded. The
// insertion succeeds if the key is not already in the map and fails
// otherwise
// This example shows you the result of trying to insert a second record
// with "james" into the map
pair<map<string, employee *>::iterator, bool> insertionResult
= employee_table.insert(make_pair("james", new employee(39, "james")));
cout << boolalpha << "insertion result for 2nd james = "
<< insertionResult.second
<< endl;
map<string, employee *>::iterator employee_table_iter;
employee_table_iter = employee_table.find("nels");
// the map find method returns an iterator whose "first" field points to
// the key and whose "second" field points to the value
cout << employee_table_iter->second->age << endl;
}
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Sorting a Vector of Integers
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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
main() {
vector<int> a;
a.push_back(5);
a.push_back(3);
a.push_back(7);
a.push_back(9);
a.push_back(1);
sort(a.begin(), a.end());
for (int i = 0; i < a.size(); i++)
cout << a[i] << endl;
}
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Sorting a Vector of Objects
<![CDATA[
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
class employee {
public:
int age;
string name;
employee(int emp_age, string emp_name) :
age(emp_age), name(emp_name) {}
};
// a function that compares two employees and returns true
// if the first employee's age is less than the second
// employee's age
bool emp_compare(const employee *e1, const employee *e2) {
return e1->age < e2->age;
}
main() {
vector<employee *> a;
a.push_back(new employee(5, "brad"));
a.push_back(new employee(3, "ebber"));
a.push_back(new employee(7, "smiley"));
a.push_back(new employee(9, "lady"));
a.push_back(new employee(1, "sunshine"));
sort(a.begin(), a.end(), emp_compare);
for (int i = 0; i < a.size(); i++)
cout << a[i]->age << endl;
}
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