在说指向指针的指针之前，不得不说指向变量的指针。先看如下示例：
1. 指向整型指针
先看如下示例：
1 #include <iostream>
using namespace std;
int main()
{
int a = 5;
int * p = &a;
cout << "a = " << a << endl
<< "&a = " << &a << endl
<< "*p = " << *p << endl
<< "p = " << p << endl
<< "&p = " << &p << endl;
return 0;
}
运行结果如下：
我们先看下内存分配图：
由上图可以清楚的知道，输出整形变量a的值是5，指针变量p的值是001BFD18，而*号的作用是取值，*p即取地址001BFD18中存放的值，即5。
2. 指向字符型指针
先看如下示例：
1 #include <iostream>
using namespace std;
int main()
{
char a[] = "hello";
char *p = a;
cout << "p = " << p << endl
<<"p = " << (void *) p << endl
<< "*p = " << *p << endl;
for(int i = 0 ; i < 5; i++)
{
cout << "&a[" << i << "] = "<< (void *)&a[i] << endl;
}
return 0;
}
1 #include <iostream>
2 using namespace std;
3
4 int main()
5 {
6 char a[] = "hello";
7 char *p = a;
8
9 cout << "p = " << p << endl
10 <<"p = " << (void *) p << endl
11 << "*p = " << *p << endl;
12
13
14 for(int i = 0 ; i < 5; i++)
15 {
16 cout << "&a[" << i << "] = "<< (void *)&a[i] << endl;
17 }
18 return 0;
19 }
运行结果图如下：
为什么整型指针p输出的是地址，而字符型指针输出的是字符串呢，字符型指针里存放的不是地址吗？
我们先看下内存分配图：
由上图可以看出，其实p中存放的是地址，只是当cout时，如果指针是字符型指针，那么会输出p中地址指向的内存中的内容(这里是h)直到遇到‘\0‘才结束。所以直接输出p时会输出hello，而将p强制转换为void *时输出的是地址。
3. 指向整型指针的指针
先看如下示例：
1 #include <iostream>
using namespace std;
int main()
{
int a[5] = {1, 2, 3, 4, 5};
int *p = a;
int **point = &p;
cout << "a = " << a << endl
<< "p = " << p << endl
<< "&p = " << &p << endl
<< "point = " << point << endl
<< "&point = " << &point << endl;
for (int i = 0; i < 5; i++)
{
cout << "&a[" << i << "] = " << &a[i] << endl;
}
return 0;
}
1 #include <iostream>
2 using namespace std;
3
4 int main()
5 {
6 int a[5] = {1, 2, 3, 4, 5};
7 int *p = a;
8 int **point = &p;
9
10 cout << "a = " << a << endl
11 << "p = " << p << endl
12 << "&p = " << &p << endl
13 << "point = " << point << endl
14 << "&point = " << &point << endl;
15
16 for (int i = 0; i < 5; i++)
17 {
18 cout << "&a[" << i << "] = " << &a[i] << endl;
19 }
20 return 0;
21 }
运行结果图如下：
我们先看下内存分配图：
从上图可以看出point指针中存放的是p指针的地址，而p指针中存放的是a[0]的地址。所以*point和p是一样的，前者是取point指针中存放的地址(0025F754)中的值，即取地址0025F754中存放的值(0025F760)，而后者就是0025F760，所以两者是等价的。**point和a[0]是等价的，前者可以写成*p，*p是取p中存放的地址(0025F760)中的值，即地址0025F760中存放的值1。由上可以得出*point等于p， **point 等于 a[0]。通过上图可以清晰的对付诸如*point++等问题。
4. 指向整型指针的指针
先看如下示例：
1 #include <iostream>
using namespace std;
int main()
{
char *a[] = {"Wel", "To", "China"};
char **p = a;
for(int i = 0; i < 3; i++)
{
for (int j = 0; j < strlen(a[i]) + 1; j++)
{
cout << a[i][j] << "\t" << (void *)&a[i][j] << endl;
}
cout << endl;
}
for (int i = 0; i < 3; i++)
{
cout << "a[" << i << "] = " << (void *) a[i] << endl
<< "&a[" << i << "] = " << &a[i] << endl;
}
cout << "p = " << p << endl
<< "&p = " << &p << endl;
return 0;
}
1 #include <iostream>
2 using namespace std;
3
4 int main()
5 {
6 char *a[] = {"Wel", "To", "China"};
7 char **p = a;
8 for(int i = 0; i < 3; i++)
9 {
10 for (int j = 0; j < strlen(a[i]) + 1; j++)
11 {
12 cout << a[i][j] << "\t" << (void *)&a[i][j] << endl;
13 }
14 cout << endl;
15 }
16
17 for (int i = 0; i < 3; i++)
18 {
19 cout << "a[" << i << "] = " << (void *) a[i] << endl
20 << "&a[" << i << "] = " << &a[i] << endl;
21 }
22
23
24 cout << "p = " << p << endl
25 << "&p = " << &p << endl;
26 return 0;
27 }
运行结果图如下：
我们先看下内存分配图：
由上图可以看出a[0]中存放着‘W‘的地址，a[1]中存放着‘T‘的地址，a[2]中存放着‘C‘的地址，只是这些地址都是指向字符型的，所以直接cout的会输出字符串，而指针p中存放着a[0]的地址，所以*p等于a[0],都是获得‘W‘的地址，即00A778CCC，而**p和a[0][0]等价都获得了地址00A778CCC中存放的值W。由上图我们可以看到字符地址相隔1个字节，而指针地址相隔4个字节，这样就便于++运算，获得下一个地址了，列如++p后，p就指向a[1]，p中存放的是a[1]的地址。