二進制搜索字符串無法正常工作

Question

以下程序是一個清單菜單。 由於某些原因，除了我搜索產品名稱（選項3）函數lookupName之外，其他所有內容似乎都可以正常工作。 在將條件設置為什么都沒有返回之前，它一直在工作，以給出錯誤消息，這與我用於lookupSku的相同，並且工作正常。 我不確定代碼有什么問題了。

#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>


using namespace std;

struct inventory {

  string name;
  int sku;
  int quantity;
  double price;
};

int size = 0;

void fillArray ( inventory[], int&, ifstream& );
void sortArray ( inventory[], int );
void displayIn ( inventory[], int );
int lookupSku ( inventory[], int, int );
int lookupName ( inventory[], int, string );

int main(){
  // Constants for menu choices
  const int DISPLAY_INVENTORY = 1,
            LOOKUP_SKU = 2,
            LOOKUP_NAME = 3,
            QUIT_CHOICE = 4;

  int choice;

  inventory products [100];

  ifstream fin;
  fin.open ("inventory.dat");

  if (!fin)
  {
    cout << endl << endl
         << " ***Program Terminated. *** " << endl << endl
         << " Input file failed to open. " << endl;

    system ( "PAUSE>NUL" );

    return 1;
  }

  fillArray ( products, size, fin );
  sortArray ( products, size );

   // Set up numeric output formatting.
   cout << fixed << showpoint << setprecision(2);

   do
   {
      // Display the menu.
      cout << "\n\t\t Manage Inventory Menu\n\n"
           << "1. Display inventory sorted by sku\n"
           << "2. Lookup a product by sku\n"
           << "3. Lookup a product by name\n"
           << "4. Quit the Program\n\n"
           << "Enter your choice: ";
      cin >> choice;
      cout << endl;

      // Validate the menu selection.
      while (choice < DISPLAY_INVENTORY || choice > QUIT_CHOICE)
      {
         cout << "Please enter a valid menu choice: ";
         cin >> choice;
      }

      // Validate and process the user's choice.
      if (choice != QUIT_CHOICE)
      {
         int indexSku,
             indexName,
             skuChoice;

         string nameChoice;

         switch (choice)
         {
            case DISPLAY_INVENTORY:
                displayIn ( products, size );
            break;

            case LOOKUP_SKU:
                cout << "Enter the Sku number: ";
                cin >> skuChoice;
                cout << endl;

                indexSku = lookupSku( products, size, skuChoice );

                if ( indexSku >= 0 )
                {
                  cout << "Product Name: " << products[indexSku].name << endl
                       << "Sku: " << products[indexSku].sku << endl
                       << "Quantity: " << products[indexSku].quantity << endl
                       << "Price: " << products[indexSku].price << endl;
                }
                else
                  cout << "No product found with this sku!" << endl;

            break;

            case LOOKUP_NAME:
                cout << "Enter product name with no spaces: ";
                cin >> nameChoice;
                cout << endl;

                indexName = lookupName( products, size, nameChoice );

                if ( indexName >= 0 )
                {
                  cout << "Product Name: " << products[indexName].name << endl
                       << "Sku: " << products[indexName].sku << endl
                       << "Quantity: " << products[indexName].quantity << endl
                       << "Price: " << products[indexName].price << endl;
                }
                else
                  cout << "No product found with this product name!" << endl;

            break;
         }

      }
   } while (choice != QUIT_CHOICE);

 fin.close ();

 return 0;
}

void fillArray ( inventory product[], int &size, ifstream &fin )
{
  int counter = 0;

  while (fin >> product[counter].name)
  {
     fin >>  product[counter].sku>> product[counter].quantity
         >> product[counter].price;

     counter ++;
  }

  size = counter;
}

void sortArray ( inventory product[], int size )
{
   bool swap;

   do
   {
      swap = false;
      for (int count = 0; count < (size - 1); count++)
      {
         if ( product[count].sku > product[count + 1].sku )
         {
            inventory temp = product[count];
            product[count] = product[count + 1];
            product[count + 1] = temp;

            swap = true;
         }
      }
   } while (swap);
}


void displayIn ( inventory product[], int size )
{
  for ( int i = 0; i < size; i++ )

  cout << product[i].sku << "    " <<  product[i].quantity << "     "
       <<  product[i].price << "    " << setw(4) <<  product[i].name << endl;
}

int lookupSku(inventory product[], int size, int value)
{
   int first = 0,
       last = size - 1,
       middle,
       position = -1;
   bool found = false;

   while (!found && first <= last)
   {
      middle = (first + last) / 2;
      if (product[middle].sku == value)
      {
         found = true;
         position = middle;
      }
      else if (product[middle].sku > value)
         last = middle - 1;
      else
         first = middle + 1;
   }
   return position;
}

int lookupName ( inventory product[], int size , string value )
{
   int first = 0,
       last = size - 1,
       middle,
       position = -1;
   bool found = false;

   while (!found && first <= last)
   {
      middle = (first + last) / 2;
      if (product[middle].name == value)
      {
         found = true;
         position = middle;
      }
      else if (product[middle].name > value)
         last = middle - 1;
      else
         first = middle + 1;
   }
   return position;
}

Answer 1

您使用“二進制搜索”查找產品名稱的代碼是正確的，但是看來數據是按SKU排序的。 二進制搜索算法僅在對數據進行排序時才有效。

您可以修改程序，以在應用二進制搜索之前按產品名稱對數據進行排序，但是在這種情況下，由於使用的是冒泡排序，即N ^ 2搜索時間，因此最好通過線性搜索來實現。產品名稱。