chap22.lst

C++捷径教程_code C++用户的良好代码资源。

listing 1
#define UP 1
#define DOWN 0

listing 2
cout << UP << ' ' << DOWN << ' ' << UP + UP;

listing 3
#define ONE   1
#define TWO   ONE+ONE
#define THREE ONE+TWO

listing 4
#define GETFILE "Enter File Name"

.
.
.

cout << GETFILE;

listing 5
cout << "Enter File Name";

listing 6
#define GETFILE "Enter File Name"
.
.
.
cout << "GETFILE is a macro name\n";

listing 7
#define LONG_STRING "this is a very long \
string that is used as an example"

listing 8
#define MAX_SIZE 100
// ...
float balance[MAX_SIZE];
double indexMAX_SIZE;
int num_emp[MAX_SIZE]; 

listing 9
// Use a function-like macro.
#include <iostream>
using namespace std;

#define MIN(a,b)  (((a)<(b)) ? a : b)

int main()
{
  int x, y;

  x = 10;
  y = 20;
  cout << "The minimum is " << MIN(x, y);

  return 0;
}

listing 10
cout << "The minimum is: " << ((x)<(y)) ? x : y);

listing 11
// This program will give the wrong answer.
#include <iostream>
using namespace std;

#define EVEN(a) a%2==0 ? 1 : 0

int main()
{
  if(EVEN(9+1)) cout << "is even";
  else cout << "is odd";

  return 0;
}

listing 12
9+1%2==0 ? 1 : 0

listing 13
// This program is now fixed.
#include <iostream>
using namespace std;

#define EVEN(a) (a)%2==0 ? 1 : 0

int main()
{
  if(EVEN(9+1)) cout << "is even";
  else cout << "is odd";

  return 0;
}

listing 14
#include <vector>

listing 15
#include <sample.h>
#include "sample.h"

listing 16
// A simple #if example.
#include <iostream>
using namespace std;

#define MAX 100
int main()
{
#if MAX>10
  cout << "Extra memory required.\n";
#endif

  // ...
  return 0;
}

listing 17
// A simple #if/#else example.
#include <iostream>
using namespace std;

#define MAX 6
int main()
{
#if MAX>10
  cout << "Extra memory required.\n");
#else
  cout << "Current memory OK.\n";
#endif

  // ...

  return 0;
}

listing 18
#define JOHN 0
#define BOB 1
#define TOM 2

#define COMPILED_BY JOHN

#if COMPILED_BY == JOHN
  char who[] = "John";
#elif COMPILED_BY == BOB
  char who[] = "Bob";
#else
  char who[] = "Tom";
#endif

listing 19
#if COMPILED_BY == BOB
   #if DEBUG == FULL
      int port = 198;
   #elif DEBUG == PARTIAL
      int port = 200;
   #endif
#else
   cout << "Bob must compile for debug output.\n";
#endif

listing 20
#include <iostream>
using namespace std;

#define TOM

int main()
{
#ifdef TOM
  cout << "Programmer is Tom.\n";
#else
  cout << "Programmer is unknown.\n";
#endif
#ifndef RALPH
  cout << "RALPH not defined.\n";
#endif
  return 0;
}

listing 21
#define TIMEOUT 100
#define WAIT 0

// ...

#undef TIMEOUT
#undef WAIT

listing 22
#if defined MYFILE

listing 24
#if !defined DEBUG
  cout << "Final version!\n";
#endif

listing 25
#include <iostream>
using namespace std;

#line 200            // set line counter to 200
int main()           // now this is line 200
{                    // this is line 201
  cout <<  __LINE__; // prints 202

  return 0;
}

listing 26
#include <iostream>
using namespace std;

#define mkstr(s)  # s

int main()
{
  cout << mkstr(I like C++);

  return 0;
}

listing 27
cout << mkstr(I like C++);

listing 28
cout << "I like C++";

listing 29
#include <iostream>
using namespace std;

#define concat(a, b)  a ## b

int main()
{
  int xy = 10;

  cout << concat(x, y);

  return 0;
}

listing 30
cout << concat(x, y);

listing 31
cout << xy;