5.C++：string常用函数及模拟实现

一、resize() 

void test7()
{
    string s("hello world");
    s.resize(5);  //改变长度
    s.resize(20,'x');  //改变空间大小
} 
int main()
{
    test7();
    return 0;
}

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二、string常用函数接口 

1.打印

2.+=、push_back、append

3.迭代器，读写；s.begin()、s.end()、s.rbegin()、s.rend()

4. s.size()、s.length()、s.capacity()

5.s.reserve(100)、s.resize(100,'x')

6.s.insert(0,"x")、s.insert(s.begin(),"x")

7.s.erase(2,3)

8.s.substr(2,3) //从下标为2开始，往后打印3个

9.< >,比较的是字符的ascii码

10.getline(cin,s1),遇到换行结束；cin>>s1,遇到换行或空格结束

#include <iostream>
#include <string>
using namespace std;
//1.常规用法
void test1()
{
	string s1;
	string s2("hello");
	string s3(s2);    //拷贝构造
	string s4("hello",2); //he，打印前两个
	string s5("hello",1,2); //el，从第二个开始打印
	cout << s1 << endl;
	cout << s2 << endl;
	cout << s3 << endl;
	cout << s4 << endl;
	cout << s5 << endl;
}
//2.读和写
void test2()
{
	string s1("hello");
	s1 += ' ';
	s1 += "world";
	cout << s1 << endl;
	//写
	for (size_t i=0; i<s1.size(); i++)
	{
		s1[i] += 1;
	}
	//读
	for (size_t i = 0; i < s1.size(); i++)
	{
		cout << s1[i]<<' ';
	}
	cout << endl;
	//迭代器 写
	string::iterator it = s1.begin(); //可将it看作指针
	while (it != s1.end())  //end指向‘o’后面的位置
	{
		*it -= 1;
		++it;
	}
	//迭代器 读
	it = s1.begin();
	while (it != s1.end())
	{
		cout << *it << " ";
		++it;
	}
	cout << endl;
}
//3.倒着遍历
void test3()
{
	string s1("hello");
	string::reverse_iterator rit = s1.rbegin();
	whi