libstdc++-v3/testsuite/ext/pb_ds/example/basic_multimap.cc

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2005-2013 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the terms
   7 // of the GNU General Public License as published by the Free Software
   8 // Foundation; either version 3, or (at your option) any later
   9 // version.
  10
  11 // This library is distributed in the hope that it will be useful, but
  12 // WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 // General Public License for more details.
  15
  16 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING3.  If not see
  18 // <http://www.gnu.org/licenses/>.
  19
  20
  21 // Copyright (C) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.
  22
  23 // Permission to use, copy, modify, sell, and distribute this software
  24 // is hereby granted without fee, provided that the above copyright
  25 // notice appears in all copies, and that both that copyright notice
  26 // and this permission notice appear in supporting documentation. None
  27 // of the above authors, nor IBM Haifa Research Laboratories, make any
  28 // representation about the suitability of this software for any
  29 // purpose. It is provided "as is" without express or implied
  30 // warranty.
  31
  32 /**
  33  * @file basic_multimap_example.cpp
  34  * A basic example showing how to use multimaps.
  35  */
  36
  37 /**
  38  * This example shows how to use "multimaps" in the context of a simple
  39  * bank account application. Each customer holds a bank account
  40  * (or more than one) which holds some balance.
  41  */
  42
  43 #include <iostream>
  44 #include <string>
  45 #include <cassert>
  46 #include <ext/pb_ds/assoc_container.hpp>
  47
  48 using namespace std;
  49 using namespace __gnu_pbds;
  50
  51 // A simple hash functor.
  52 // hash could serve instead of this functor, but it is not yet
  53 // standard everywhere.
  54 struct string_hash : public unary_function<string, size_t>
  55 {
  56   inline size_t
  57   operator()(const string& r_s) const
  58   {
  59     size_t ret = 0;
  60     string::const_iterator b = r_s.begin();
  61     string::const_iterator e = r_s.end();
  62     while (b != e)
  63       {
  64         ret *= 5;
  65         ret += static_cast<size_t>(*(b++));
  66       }
  67     return ret;
  68   }
  69 };
  70
  71 int main()
  72 {
  73   // Each customer is identified by a string.
  74   typedef string customer;
  75
  76   // Each account is identified by an unsigned long.
  77   typedef unsigned long account_id;
  78
  79   // The balance in the account is a floating point.
  80   typedef float balance_t;
  81
  82   /*
  83    *  This is the data structure type used for storing information
  84    *  about accounts. In this case the primary key is the customer,
  85    *  and the secondary key is the account id.
  86    *
  87    *  A hash-based container maps each customer to a list-based
  88    *  container that maps each account to the balance it holds.
  89    *
  90    *  Note that we could use any combination of primary and secondary
  91    *  associative-containers. In this case we choose a hash-based
  92    *  container for the primary keys, since we do not need to store
  93    *  customers in a sorted order; we choos a list-based container for
  94    *  the secondary keys, since we expect that the average number of
  95    *  accounts per customer will be small.
  96    */
  97   typedef
  98     cc_hash_table<
  99     customer,
 100     list_update<
 101     account_id,
 102     balance_t>,
 103     string_hash>
 104     accounts_t;
 105
 106   // This object will hold all information.
 107   accounts_t acc;
 108
 109   // Customer "a" opens empty account 12.
 110   acc["a"][12] = 0;
 111
 112   // Customer "a" deposits 45 into account 12.
 113   acc["a"][12] += 45;
 114
 115   // Customer "b" opens account 13 with balance 12.3.
 116   acc["b"][13] = 12.3;
 117
 118   // Customer "c" opens empty account 14.
 119   acc["c"][14] = 0;
 120
 121   // Customer "a" opens account 160 with balance 142.
 122   // Note that "a" already holds account 12.
 123   acc["a"][160] = 142;
 124
 125   // Verify the number of accounts that "a" holds.
 126   accounts_t::point_const_iterator it = acc.find("a");
 127   assert(it != acc.end());
 128   assert(it->second.size() == 2);
 129
 130   // The begining of the month has arrived. We need to give a 3%
 131   // interest to all accounts with a positive balance.
 132
 133   // First we loop over all customers.
 134   accounts_t::iterator cust_it;
 135   for (cust_it = acc.begin(); cust_it != acc.end(); ++cust_it)
 136     {
 137       // For each customer, we loop over the customer's accounts.
 138       accounts_t::mapped_type::iterator it;
 139       for (it = cust_it->second.begin(); it != cust_it->second.end(); ++it)
 140         if (it->second > 0)
 141           it->second *= 1.03;
 142     }
 143
 144   // Customer "a" closes all accounts.
 145   acc.erase("a");
 146
 147   // The bank now has only 2 customers.
 148   assert(acc.size() == 2);
 149
 150   return 0;
 151 }
 152