36-指针、数组和指针算术

4.8　指针、数组和指针算术

指针和数组基本等价的原因在于指针算术（pointer arithmetic）和C++内部处理数组的方式。首先，我们来看一看算术。将整数变量加1后，其值将增加1；但将指针变量加1后，增加的量等于它指向的类型的字节数。将指向double的指针加1后，如果系统对double使用8个字节存储，则数值将增加8；将指向short的指针加1后，如果系统对short使用2个字节存储，则指针值将增加2。程序清单4.19演示了这种令人吃惊的现象，它还说明了另一点：C++将数组名解释为地址。

程序清单4.19　addpntrs.cpp

// addpntrs.cpp -- pointer addition
#include <iostream>
int main()
{
    using namespace std;
    double wages[3] = {10000.0, 20000.0, 30000.0};
    short stacks[3] = {3, 2, 1};
// Here are two ways to get the address of an array
    double * pw = wages; // name of an array = address
    short * ps = &stacks[0]; // or use address operator
// with array element
    cout << "pw = " << pw << ", *pw = " << *pw << endl;
    pw = pw + 1;
    cout << "add 1 to the pw pointer:\n";
    cout << "pw = " << pw << ", *pw = " << *pw << "\n\n";
    cout << "ps = " << ps << ", *ps = " << *ps << endl;
    ps = ps + 1;
    cout << "add 1 to the ps pointer:\n";
    cout << "ps = " << ps << ", *ps = " << *ps << "\n\n";
    cout << "access two elements with array notation\n";
    cout << "stacks[0] = " << stacks[0]
         << ", stacks[1] = " << stacks[1] << endl;
    cout << "access two elements with pointer notation\n";
    cout << "*stacks = " << *stacks
         << ", *(stacks + 1) = " << *(stacks + 1) << endl;
    cout << sizeof(wages) << " = size of wages array\n";
    cout << sizeof(pw) << " = size of pw pointer\n";
    return 0;
}

下面是该程序的输出：

pw = 0x28ccf0, *pw = 10000
add 1 to the pw pointer:
pw = 0x28ccf8, *pw = 20000
ps = 0x28ccea, *ps = 3
add 1 to the ps pointer:
ps = 0x28ccec, *ps = 2
access two elements with array notation
stacks[0] = 3, stacks[1] = 2
access two elements with pointer notation
*stacks = 3, *(stacks + 1) = 2
24 = size of wages array
4 = size of pw pointer