C++指針學習

最簡單的指針使用   
#include <iostream>
#include <stdlib.h>
 
using namespace std;
 
int main()
{
    int i = 30;
 
    std::cout << "&i = "<< &i << std::endl;
    std::cout << "i =  " << i << std::endl;
 
    int *pi = NULL; //初始為空  表明該指針不指向一個可訪問的內存位置
    pi = &i;//把 i 地址的編號賦值給 pi    。指針變量所存的內容就是內存的地址編號 
    std::cout << "*pi = " << *pi << std::endl;
    return 0;
}
結果如下

&i = 0x7ffeb3485828
i = 30
*pi = 30

指針算法運算
#include <iostream>
using namespace std;
const int MAX = 3;
 
int main ()
{
   int  var[MAX] = {10, 100, 200};
   int  *ptr;
 
   // 指針中第一個元素的地址
   ptr = var;   // 不需要加取地址符
   for (int i = 0; i < MAX; i++)
   {
      cout << "Address of var[" << i << "] = ";
      cout << ptr << endl;
 
      cout << "Value of var[" << i << "] = ";
      cout << *ptr << endl;
 
      // 移動到下一個位置
      ptr++;  
   }
   return 0;
}

Address of var[0] = 0xbfce42d0
Value of var[0] = 10
Address of var[1] = 0xbfce42d4
Value of var[1] = 100
Address of var[2] = 0xbfce42d8
Value of var[2] = 200

傳遞指針給函數    總體上可以理解成全局變量  因為傳的是地址， 修改之后在另一個函數內也變化
#include <iostream>
#include <ctime>
 
using namespace std;
void get(unsigned long *par);
int main ()
{
   unsigned long sec = 10;
   get( &sec );
   cout << "sec: " << sec << endl;
   return 0;
}
 
void get(unsigned long *par)
{
   *par = *par * *par;
   return;
}

sec: 100

#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;
// 要生成和返回隨機數的函數
int * getRandom( ) //返回指針
{
  static int  r[10];
  // 設置種子
  srand( (unsigned)time( NULL ) );
  for (int i = 0; i < 10; ++i)
  {
    r[i] = i;
    cout << r[i] << endl;
  }
  return r;
}
// 要調用上面定義函數的主函數
int main ()
{
   // 一個指向整數的指針
   int *p;
   p = getRandom();
   for ( int i = 0; i < 10; i++ )
   {
       cout << "*(p + " << i << ") : ";
       cout << *(p + i) << endl;
   }
   return 0;
}