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  1. #include <iostream>
  2. #include <vector>
  3. #include <algorithm>
  4.  
  5. using namespace std;
  6.  
  7. class DBConn {
  8. private:
  9.     int id;
  10.     DBConn(int conn_id) : id(conn_id) {
  11.         cout << "Connection " << id << " established.\n";
  12.     }
  13.     ~DBConn() {
  14.         cout << "Connection " << id << " closed.\n";
  15.     }
  16.  
  17. public:
  18.     void query(const string& sql) {
  19.         cout << "Executing on Connection " << id << ": " << sql << endl;
  20.     }
  21.     friend class ConnManager; // Only ConnManager can create/destroy
  22. };
  23.  
  24. class ConnManager {
  25. private:
  26.     static vector<DBConn*> connections;
  27.     static int connCounter;
  28. public:
  29.     // Get a new database connection
  30.     static DBConn* getConn() {
  31.         DBConn* conn = new DBConn(++connCounter);
  32.         connections.push_back(conn);
  33.         return conn;
  34.     }
  35.     // Release a specific connection
  36.     static void releaseConn(DBConn* conn) {
  37.         auto it = find(connections.begin(), connections.end(), conn);
  38.         if (it != connections.end()) {
  39.             delete *it;
  40.             connections.erase(it);
  41.             cout << "Connection released.\n";
  42.         } 
  43.         else
  44.             cout << "Invalid connection!\n";
  45.     }
  46.     // Close all connections
  47.     static void shutdownAll() {
  48.         cout << "Shutting down all connections\n";
  49.         for (DBConn* conn : connections) {
  50.             delete conn;
  51.         }
  52.         connections.clear();
  53.         cout << "All connections closed.\n";
  54.     }
  55. };
  56. // Static variable initialization
  57. vector<DBConn*> ConnManager::connections;
  58. int ConnManager::connCounter = 0;
  59. // Driver Code
  60. int main() {
  61.     cout << "\n--- Creating Database Connections ---" << endl;
  62.     DBConn* db1 = ConnManager::getConn();
  63.     DBConn* db2 = ConnManager::getConn();
  64.     db1->query("SELECT * FROM users");
  65.     db2->query("UPDATE users SET active = 1");
  66.     cout << "\n--- Releasing One Connection ---" << endl;
  67.     ConnManager::releaseConn(db1);
  68.     cout << "\n--- Shutting Down All Connections ---" << endl;
  69.     ConnManager::shutdownAll();
  70.     return 0;
  71. }
  72.  
Success #stdin #stdout 0s 5296KB
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stdin
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stdout
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--- Creating Database Connections ---
Connection 1 established.
Connection 2 established.
Executing on Connection 1: SELECT * FROM users
Executing on Connection 2: UPDATE users SET active = 1

--- Releasing One Connection ---
Connection 1 closed.
Connection released.

--- Shutting Down All Connections ---
Shutting down all connections
Connection 2 closed.
All connections closed.
https://ideone.com/pTJBkf
language:
C++ 4.3.2 (gcc-4.3.2)
created:
12 days ago
visibility:
public

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