C++数组和指针

Part one
在用到数组名的地方，便会将其转换为指向数组第一个元素的指针
char a[ ] = { };
auto p = a; //等价于 p = &a[0];

#include<iostream>
#include<string>
using namespace std;
void main() {
	char a[4] = {'a','b','a','d'};
	auto p = a;
	auto q = &a[4];   //p为指向数组a的未元素的下一个地址的指针；
	for (p; p != q; ++p)
		cout << *p<< endl;
	auto size_a = size(a);
	cout << size_a << endl;
	system("pause");
}

输出：

利用begin、end 函数避免手动确定数组起止地址指针可能会引发的错误；

#include<iostream>
#include<string>
using namespace std;
void main() {
	char a[4] = { 'a','b','a','d' };
	char *p = begin(a);
	char *q = end(a);   //p为指向数组a的未元素的下一个地址的指针；
	for (p; p != q; ++p)
		cout << *p << endl;
	system("pause");
}

**Part two
给指针加上或者减去一个整数值，其结果仍然是指针。**新指针指向的元素与原来的指针相比前进（加）或后退（减）了该整数值个位置；

    #include<iostream>
	using namespace std;
	void main() {
	char a[4] = { 'a','b','a','d' };
	char *p = a;
	char *q = p + 3;
	char *m = q - 2;
	char *n = q - 6;  //已超出数组范围
	cout << "p = " << *p << endl;
	cout << "q = " << *q << endl;
	cout << "m = " << *m << endl;
	cout << "n = " << *n << endl;  
	system("pause");
}

n为空。

Part three
两个指针相减，结果是他们之间的距离。
参与运算的两个指针必须指向同一个数组中的元素；
两个指针相减的结果是一种类型名为ptrdiff_t的标准库类型，因为两个指针相减差值可能为负，因此ptrdiff_t是一种带符号数。

#include<iostream>
using namespace std;
void main() {
	char a[4] = { 'a','b','a','d' };
	char *p = a;
	char *q = &a[3];
	auto len = q - p;   //不确定是啥类型，用auto就好
	auto length = p - q;;
	cout << "p = " << *p << endl;
	cout << "q = " << *q << endl;
	cout << "len = " << len << endl;
	cout << "length = " << length << endl;
	system("pause");
}

Part four
下标和指针

#include<iostream>
using namespace std;
void main() {
	char a[4] = { 'a','b','c','d' };
	char *p = a;	// p = &a[0];
	char *q = &a[2];
	char m = *(p + 2);  // m == a[2] == *q == 'c';
	char n = q[1];		// n == *(q+1) == a[3] == 'd';
	char t = q[-1];		// t == *(q-1) == a[1] == 'b';

	cout << "p = " << *p << endl;
	cout << "q = " << *q << endl;
	cout << "m = " << m << endl;
	cout << "n = " << n << endl;
	cout << "t = " << t << endl;
	system("pause");
}