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 vector of name/count pairs, storing the
// number of times each name shows up in the raw data.
//
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 (nameExists(name)) {
      // If the name exists in the database, just
      // increment the count
      incrementNameCount(name);
    } else {
      // If the name doesn't yet exist, add it with
      // a count of 1.
      addNewName(name);
    }
  }
  inFile.close();
}

//
// nameExists
//
// Returns true if the name exists in the database. Returns false otherwise.
//
bool NameDB::nameExists(const string& name) const
{
  // Iterate through the vector of names looking for the name.
  for (vector<pair<string, int> >::const_iterator it = mNames.begin();
       it !=  mNames.end(); ++it) {
    if (it->first == name) {
      return (true);
    }
  }
  return (false);
}

//
// incrementNameCount
//
// Precondition: name exists in the vector of names.
// Postcondition: the count associated with name is incremented.
//
void NameDB::incrementNameCount(const string& name)
{
  for (vector<pair<string, int> >::iterator it = mNames.begin();
       it != mNames.end(); ++it) {
    if (it->first == name) {
      it->second++;
      return;
    }
  }
}

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

//
// getNameRank
//
// Returns the rank of the name.
// First looks up the name to obtain the number of babies with that name.
// Then iterates through all the names, counting all the names with a higher
// count than the specified name. Returns that count as the rank.
//
int NameDB::getNameRank(const string& name) const
{
  // Make use of the getAbsoluteNumber() method
  int num = getAbsoluteNumber(name);

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

  //
  // Now count all the names in the vector that have a
  // 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 (vector<pair<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
{
  for (vector<pair<string, int> >::const_iterator it = mNames.begin();
       it != mNames.end(); ++it) {
    if (it->first == name) {
      return(it->second);
    }
  }
  return (-1);
}