void test_string1()
{
	//1.string();
	cout << "1." << endl;
	string s1;
	cout << s1 << endl;

	//2.string(const char* s)
	cout << "2." << endl;
	string s2("hello world!!!");
	cout << s2 << endl;

	//3.string(const string& str)
	cout << "3." << endl;
	string s3(s2);
	cout << s3 << endl;

	//4.string(const string& str, size_t pos, size_t len = npos)
	cout << "4." << endl;
	string s4(s3, 6, 4);
	cout << s4 << endl;
	string s5(s3, 6, 20);
	cout << s5 << endl;
	string s6(s3, 6);
	cout << s6 << endl;

	//5.string(const char* s, size_t n);
	cout << "5." << endl;
	string s7("hello world", 4);
	cout << s7 << endl;

	//6.string(size_t n, char c)
	cout << "6." << endl;
	string s8(5, 'm');
	cout << s8 << endl;

	//7.迭代器版本
	cout << "7." << endl;
	string s9("helloooooo");
	string s10(s9.begin(), s9.end() - 5);
	cout << s10 << endl;
}

2.赋值运算符重载

void test_string2()
{
	//1.string& operator=(const string& str)
	cout << "1." << endl;
	string s1("hello world!");
	string s2("hello string!");
	s1 = s2;
	cout << s1 << endl;

	//2.string& operator=(const char* s)
	cout << "2." << endl;
	string s3("ni hao");
	s3 = "hello";
	cout << s3 << endl;

	//3.string& operator=(char c)
	cout << "3." << endl;
	string s4("hhhhhh");
	s4 = 'h';
	cout << s4 << endl;
}

3.逐个字符遍历：[]重载与at

void test_string3()
{
	//char& operator[](size_t pos)
	cout << "1." << endl;
	string s1("helloworld!");
	for (size_t i = 0; i < s1.size(); i++)
	{
		cout << s1[i] << " ";
	}
	cout << endl;

	//const char& operator[](size_t pos)
	cout << "2." << endl;
	const string s2("helloworld!");
	for (size_t i = 0; i < s2.size(); i++)
	{
		cout << s2[i] << " ";
	}
	cout << endl;

	//char& at(size_t pos)
	cout << "3." << endl;
	const string s3("helloat");
	for (size_t i = 0; i < s3.size(); i++)
	{
		cout << s3.at(i) << " ";
	}
	cout << endl;

	//const char& at(size_t pos) const
	cout << "4." << endl;
	const string s4("helloat");
	for (size_t i = 0; i < s4.size(); i++)
	{
		cout << s4.at(i) << " ";
	}
	cout << endl;
}

?3.0.范围for

void test_for()
{
	string s("hello world!!");
	for (auto ch : s)
	{
		cout << ch << " ";
	}
	cout << endl;
}

?范围for遍历的底层实际就是迭代器，可以从汇编角度观察到

4.迭代器(正向/反向/正向常量/反向常量迭代器)

void test_string4()
{
	//正向迭代器 - iterator
	//[s.begin(),s.end()) - 左闭右开
	cout << "1." << endl;
	string s1("hello iterator");
	string::iterator it = s1.begin();
	while (it != s1.end())
	{
		cout << *it << " ";
		it++;
	}
	cout << endl;

	//反向迭代器 - reverse_iterator
	//(s.rend(),s.rbegin()] - 左开右闭
	cout << "2." << endl;
	string s2("hello reverse_iterator");
	string::reverse_iterator rit = s2.rbegin();
	while (rit != s2.rend())
	{
		//正/反向迭代器可以通过it修改内容
		*rit = 'x';
		cout << *rit << " ";
		rit++;
	}
	cout << endl;
	cout << s2 << endl;

	//常量迭代器 - const_iterator
	cout << "3." << endl;
	const string s3("hello const_iterator");
	//auto cit = s3.begin();自动推导 begin返回什么auto就是什么
	string::const_iterator cit = s3.begin();
	while (cit != s3.end())
	{
		cout << *cit << " ";
		cit++;
	}
	cout << endl;

	//反向常量迭代器 - const_reverse_iterator
	cout << "4." << endl;
	const string s4("hello const_reverse_iterator");
	string::const_reverse_iterator crit = s4.rbegin();
	while (crit != s4.rend())
	{
		cout << *crit << " ";
		crit++;
	}
	cout << endl;
}

5.追加字符/字符串：push_back、append、operator+=

void test_string5()
{
	cout << "1." << endl;
	string s1("hello push_back");
	s1.push_back('a');
	cout << s1 << endl;

	cout << "2." << endl;
	string s2("hello append");
	s2.append("aaaaa");
	cout << s2 << endl;

	cout << "3." << endl;
	string s3("hello operator+=");
	s3 += "hehe";
	s3 += 'a';
	cout << s3 << endl;

	cout << "4." << endl;
	string s4("hello");
	s4.append(s3.begin(), s3.end() - 5);
	cout << s4 << endl;
}

6.capacity(容量，不包括\0所占空间)，max_size，reserve，resize

void test_string7()
{
	cout << "1." << endl;
	string s1("hello");
	cout << s1.max_size() << endl;
	cout << s1.capacity() << endl;

	//查看vs下的扩容机制
	cout << "查看vs下的扩容机制:" << endl;
	size_t sz = s1.capacity();
	for (size_t i = 0; i < 100; i++)
	{
		s1.push_back('a');
		if (sz != s1.capacity())
		{
			sz = s1.capacity();
			cout << "capacity:" << sz << endl;
		}
	}

	cout << "2." << endl;
	string s2("aaaaaaaaaaaaaaaaa");
	cout << "reserve之前capacity:" << s2.capacity() << endl;
	s2.reserve(1000);//开空间
	cout << "reserve之后capacity:" << s2.capacity() << endl;
	s2.resize(1000,'x');//开空间+初始化
	cout << "resize之后capacity:" << s2.capacity() << endl;
}

注意：空间只可扩容不可缩小，reverse或者resize开出去的空间多大就是多大，例如第一次reverse(1000)第二次reverse(500)由于第二次比第一次小，空间就按照第一次来算?

7.assign赋值，insert插入，erase删除，replace替换

void test_string8()
{
	cout << "1." << endl;
	string s1;
	s1.assign("hehe");
	cout << s1 << endl;

	cout << "2." << endl;
	string s2("hello insert");
	s2.insert(1, " OH! ");//在pos为1的位置后插入字符串
	cout << s2 << endl;
	//iterator insert (const_iterator p, char c);
	s2.insert(s2.begin(), 'K');
	cout << s2 << endl;

	s2.erase(0, 1);//在0位置向后删除1个字符
	s2.erase(s2.begin() + 2);
	cout << s2 << endl;

	cout << "3." << endl;
	string s3("helloworld");
	string s4("zsl");
	s3.replace(0, 5, s4);//将0~5替换成s4
	cout << s3 << endl;
}

注意：尽量少使用插入，删除，替换这些接口，因为底层实现是要大量挪动数据的，时间复杂度较高?

8.c_str，给C库提供的接口

void test_string9()
{
	string s1("string.cpp");
	FILE* p = fopen(s1.c_str(), "r");
	assert(p);
	char ch = 0;
	while (ch != EOF)
	{
		ch = fgetc(p);
		cout << ch;
	}
	cout << endl;

	s1 += '\0';
	s1 += "hehehe";
	cout << s1 << endl;//以size为结束标准
	cout << s1.c_str() << endl;//以'\0'为结束标准
}

许多软件的底层使用C语言实现，因为C++兼容C，使用C实现接口，C、C++都可以使用。

例如：fopen是C语言标准库提供的接口，参数不认识string这样的类，所以传参一般要传字符串的首字符地址，就可以使用c_str()这个接口将string类转换为地址，返回值为const char*

9.find、rfind、substr

void test_string10()
{
    //查找文件后缀
	//从前向后找
	cout << "1." << endl;
	string s1("string.cpp");
	size_t pos1 = s1.find(".");
	cout << s1.substr(pos1) << endl;
	//从后向前找
	cout << "2." << endl;
	string s2("hello.world.cpp");
	size_t pos2 = s2.rfind(".");
	cout << s2.substr(pos2) << endl;
}

注意：find()中传的参数要全部匹配上才可以，与下一条(10.)有明显区别

10.?find_first_of、find_last_of、find_first_not_of、find_last_not_of

void test_string11()
{
	cout << "1." << endl;
	string s1("hello,This,is,my,world!");
	size_t pos1 = 0;
	while (1)
	{
		pos1 = s1.find_first_of("l,!");
		if (pos1 == string::npos)
			break;
		s1[pos1] = '*';
		cout << s1 << endl;
	}

	cout << "2." << endl;
	string s2("hello,This,is,my,world!");
	size_t pos2 = 0;
	while (1)
	{
		pos2 = s2.find_first_not_of("l,!");
		if (pos2 == string::npos)
			break;
		s2[pos2] = ',';
		cout << s2 << endl;
	}

	cout << "3." << endl;
	string s3("hello,This,is,my,world!");
	size_t pos3 = 0;
	while (1)
	{
		pos3 = s3.find_last_of("l,!");
		if (pos3 == string::npos)
			break;
		s3[pos3] = '*';
		cout << s3 << endl;
	}
}