Referensi ke pointer

Referensi ke penunjuk dapat dideklarasikan dengan cara yang sama seperti referensi ke objek. Referensi ke penunjuk adalah nilai yang dapat dimodifikasi yang digunakan seperti penunjuk normal.

Contoh

Sampel kode ini menunjukkan perbedaan antara menggunakan penunjuk ke penunjuk dan referensi ke penunjuk.

Add1 Fungsi dan Add2 setara secara fungsional, meskipun tidak disebut dengan cara yang sama. Perbedaannya adalah menggunakan Add1 tidak langsung ganda, tetapi Add2 menggunakan kenyamanan referensi ke penunjuk.

// references_to_pointers.cpp
// compile with: /EHsc

#include <iostream>
#include <string>

// C++ Standard Library namespace
using namespace std;

enum {
   sizeOfBuffer = 132
};

// Define a binary tree structure.
struct BTree {
   char  *szText;
   BTree *Left;
   BTree *Right;
};

// Define a pointer to the root of the tree.
BTree *btRoot = 0;

int Add1( BTree **Root, char *szToAdd );
int Add2( BTree*& Root, char *szToAdd );
void PrintTree( BTree* btRoot );

int main( int argc, char *argv[] ) {
   // Usage message
   if( argc < 2 ) {
      cerr << "Usage: " << argv[0] << " [1 | 2]" << "\n";
      cerr << "\nwhere:\n";
      cerr << "1 uses double indirection\n";
      cerr << "2 uses a reference to a pointer.\n";
      cerr << "\nInput is from stdin. Use ^Z to terminate input.\n";
      return 1;
   }

   char *szBuf = new char[sizeOfBuffer];
   if (szBuf == NULL) {
      cerr << "Out of memory!\n";
      return -1;
   }

   // Read a text file from the standard input device and
   //  build a binary tree.
   while( !cin.eof() )
   {
      cin.get( szBuf, sizeOfBuffer, '\n' );
      cin.get();

      if ( strlen( szBuf ) ) {
         switch ( *argv[1] ) {
            // Method 1: Use double indirection.
            case '1':
               Add1( &btRoot, szBuf );
               break;
            // Method 2: Use reference to a pointer.
            case '2':
               Add2( btRoot, szBuf );
               break;
            default:
               cerr << "Illegal value '"
                  << *argv[1]
                  << "' supplied for add method.\n"
                     << "Choose 1 or 2.\n";
               return -1;
         }
      }
   }
   // Display the sorted list.
   PrintTree( btRoot );
}

// PrintTree: Display the binary tree in order.
void PrintTree( BTree* MybtRoot ) {
   // Traverse the left branch of the tree recursively.
   if ( MybtRoot->Left )
      PrintTree( MybtRoot->Left );

   // Print the current node.
   cout << MybtRoot->szText << "\n";

   // Traverse the right branch of the tree recursively.
   if ( MybtRoot->Right )
      PrintTree( MybtRoot->Right );
}

// Add1: Add a node to the binary tree.
//       Uses double indirection.
int Add1( BTree **Root, char *szToAdd ) {
   if ( (*Root) == 0 ) {
      (*Root) = new BTree;
      (*Root)->Left = 0;
      (*Root)->Right = 0;
      (*Root)->szText = new char[strlen( szToAdd ) + 1];
      strcpy_s((*Root)->szText, (strlen( szToAdd ) + 1), szToAdd );
      return 1;
   }
   else {
      if ( strcmp( (*Root)->szText, szToAdd ) > 0 )
         return Add1( &((*Root)->Left), szToAdd );
      else
         return Add1( &((*Root)->Right), szToAdd );
   }
}

// Add2: Add a node to the binary tree.
//       Uses reference to pointer
int Add2( BTree*& Root, char *szToAdd ) {
   if ( Root == 0 ) {
      Root = new BTree;
      Root->Left = 0;
      Root->Right = 0;
      Root->szText = new char[strlen( szToAdd ) + 1];
      strcpy_s( Root->szText, (strlen( szToAdd ) + 1), szToAdd );
      return 1;
   }
   else {
      if ( strcmp( Root->szText, szToAdd ) > 0 )
         return Add2( Root->Left, szToAdd );
      else
         return Add2( Root->Right, szToAdd );
   }
}

Usage: references_to_pointers.exe [1 | 2]

where:
1 uses double indirection
2 uses a reference to a pointer.

Input is from stdin. Use ^Z to terminate input.

Lihat juga

Referensi