prog9_08.cpp

c++最经典的入门书籍

// Program 9.8 Sorting strings recursively
#include <iostream>
#include <string>
using std::cout;
using std::cin;
using std::endl;
using std::string;

// Function prototypes
void swap(string* pStr[], int first, int second);
void sort(string* pStr[], int start, int end);
int count_words(const string& text, const string& separators);
void extract_words(string* pStr[], const string& text,
                                    const string& separators);
void show_words(string* pStr[], int count);

int main() {
  string text;                                // The string to be sorted
  const string separators = " ,.\"\n";        // Word delimiters

  // Read the string to be searched from the keyboard
  cout << endl << "Enter a string terminated by #:" << endl;
  getline(cin, text, '#');

  int word_count = count_words(text, separators); // Get count of words

  if(0 == word_count) {
    cout << endl << "No words in text." << endl;
    return 0;
  }

  string** pWords = new string*[word_count]; // Array of pntrs to words

  extract_words(pWords, text, separators);   
  sort(pWords, 0, word_count-1);             // Sort the words 
  show_words(pWords, word_count);            // Output the words

  // Delete words from free store
  for(int i = 0 ; i<word_count ; i++)
    delete pWords[i];

  // Now delete the array of pointers
  delete[] pWords;
  
  return 0;
}

// Swap address at position first with address at position second
void swap(string* pStr[], int first, int second) {
  string* temp = pStr[first];
  pStr[first] = pStr[second];
  pStr[second] = temp;
}

// Sort strings in ascending sequence
// Addresses of words to be sorted are from pStr[start] to pStr[end]
void sort(string* pStr[], int start, int end) {
  // start index must be less than end index for 2 or more elements
  if(!(start<end))
    return;                   // Less than 2 elements