详解C++编程中向函数传递引用参数的用法

// reference_type_function_arguments.cpp
struct Date
{
short DayOfWeek;
short Month;
short Day;
short Year;
};

// Create a Julian date of the form DDDYYYY
// from a Gregorian date.
long JulianFromGregorian( Date& GDate )
{
static int cDaysInMonth[] = {
31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
  };
long JDate = 0;
// Add in days for months already elapsed.
for ( int i = 0; i < GDate.Month - 1; ++i )
JDate += cDaysInMonth[i];
// Add in days for this month.
JDate += GDate.Day;

// Check for leap year.
if ( GDate.Year % 100 != 0 && GDate.Year % 4 == 0 )
JDate++;
// Add in year.
JDate *= 10000;
JDate += GDate.Year;

return JDate;
}

int main()
{
}

long JulianFromGregorian( const Date& GDate );

// refType_function_returns.cpp
// compile with: /EHsc

#include <iostream>
using namespace std;

class Point
{
public:
// Define "accessor" functions as
// reference types.
unsigned& x();
unsigned& y();
private:
// Note that these are declared at class scope:
unsigned obj_x; 
unsigned obj_y; 
};

unsigned& Point :: x()
{
return obj_x;
}
unsigned& Point :: y()
{
return obj_y;
}

int main()
{
Point ThePoint;
// Use x() and y() as l-values.
ThePoint.x() = 7;
ThePoint.y() = 9;

// Use x() and y() as r-values.
cout << "x = " << ThePoint.x() << "\n"
<< "y = " << ThePoint.y() << "\n";
}

 x = 7
y = 9

// C4172 means Don't do this!!!
Foo& GetFoo()
{
  Foo f;
  ...
  return f;
} // f is destroyed here

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

#include <iostream>
#include <string>

// STL 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: Refptr [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.\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 ( btRoot->Left )
   PrintTree( btRoot->Left );

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

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