namedb.cpp

C++高级编程这本书所附的源代码

#include "NameDB.h"

#include <fstream>

using namespace std;


//
// Reads the names from the file and populates the database.
// The database is a map associating names with their frequency.
//
NameDB::NameDB(const string& nameFile) throw (invalid_argument)
{
  //
  // Open the file and check for errors
  //
  ifstream inFile(nameFile.c_str());
  if (!inFile) {
    throw invalid_argument("Unable to open file\n");
  }

  //
  // Read the names one at a time.
  //
  string name;
  while (inFile >> name) {
    //
    // Lookup the name in the database so far.
    //
    if (!nameExistsAndIncrement(name)) {
      //
      // If the name exists in the database, the
      // function incremented it, so we just continue.
      // We get here if it didn't exist, in case which
      // we add it with a count of 1.
      //
      addNewName(name);
    }
  }
  inFile.close();
}

//
// nameExistsAndIncrement
//
// Returns true if the name exists in the database. false
// otherwise. If it finds it, it increments it.
//
bool NameDB::nameExistsAndIncrement(const string& name)
{
  //
  //Find the name in the map
  //
  map<string, int>::iterator res = mNames.find(name);
  if (res != mNames.end()) {
    res->second++;
    return (true);
  }
  return (false);
}

//
// addNewName
//
// Adds a new name to the database.
//
void NameDB::addNewName(const string& name)
{
  mNames.insert(make_pair<string, int>(name, 1));
}

//
// getNameRank
//
// Returns the
int NameDB::getNameRank(const string& name) const
{
  int num = getAbsoluteNumber(name);

  //
  // Check if we found the name
  //
  if (num == -1) {
    return (-1);
  }

  //
  // Now count all the names in the map that have 
  // count higher than this one. If no name has a higher count,
  // this name is rank number 1. Every name with a higher count
  // decreases the rank of this name by 1.
  //
  int rank = 1;
  for (map<string, int>::const_iterator it = mNames.begin();
       it != mNames.end(); ++it) {
    if (it->second > num) {
      rank++;
    }
  }

  return (rank);
}

//
// getAbsoluteNumber
//
// Returns the count associated with this name
//
int NameDB::getAbsoluteNumber(const string& name) const
{
  map<string, int>::const_iterator res = mNames.find(name);
  if (res != mNames.end()) {
    return (res->second);
  }

  return (-1);
}