C++标准库介绍及使用string类的详细过程

//使用时记得加上
#include<string>
using std::string;//或者using namespace std;
//源代码大致框架
namespace std
{
	class string
	{
	private:
		char* _str;
		size_t _size;
		size_t _capacity;
	};
}

int main()
{
	//static const size_t npos = -1;
	//typedef unsigned long long size_t
	//-1的原码：10000000 00000000 00000000 00000001
	//-1的反码：11111111 11111111 11111111 11111110
	//-1的补码：11111111 11111111 11111111 11111111
	//npos：-1的补码按照无符号整形打印出的值，由于静态成员变量，类外使用时加上类域
	cout << string::npos << endl;//32位环境：4294967295
	return 0;
}

int main()
{
	string s1;
	string s2("hello xzy");
	string s3(s2);
	string s4(s2, 6, 8);
	string s5("hello xzy", 5);
	string s6(10, 'x');
	cout << s1 << endl;//输出：
	cout << s2 << endl;//输出：hello xzy
	cout << s3 << endl;//输出：hello xzy
	cout << s4 << endl;//输出：xzy
	cout << s5 << endl;//输出：hello
	cout << s6 << endl;//输出：xxxxxxxxxx
	return 0;
}

int main()
{
	string s1;
	string s2;
	string s3;
	//赋值重载
	s1 = "hello xzy";
	s2 = s1;
	s3 = 'v';
	//拷贝构造
	string s4 = s1;
	cout << s1 << endl;//输出：hello xzy
	cout << s2 << endl;//输出：hello xzy
	cout << s3 << endl;//输出：v
	cout << s4 << endl;//输出：hello xzy
	return 0;
}

int main()
{
	string s1("hello xzy");
	s1[6] = 'w';
	s1[7] = 'j';
	s1[8] = '\0';
	cout << s1 << endl;//输出：hello wj
	s1[10] = 'A';//下标越界，内部断言assert报错
	return 0;
}

int main()
{
	string s1("hello xzy");
	string s2(" how are you");
	s1 += s2;
	cout << s1 << endl;
	s1 += "???";
	cout << s1 << endl;
	s1 += '!';
	cout << s1 << endl;
	return 0;
}

int main()
{
	string s1("hello");
	string s2 = s1 + " world";
	string s3 = "xzy " + s1;
	string s4 = s2 + s3;
	cout << s2 << endl; //hello world
	cout << s3 << endl; //xzy hello
	cout << s4 << endl; //hello worldxzy hello
	return 0;
}

int main()
{
	string s1("hello xzy");
	string::iterator it = s1.begin();
	while (it != s1.end())
	{
		cout << *it << " ";
		++it;
	}
	cout << endl;
	string s2("hello xzy");
	string::reverse_iterator rit = s2.rbegin();
	while (rit != s2.rend())
	{
		cout << *rit << " ";
		++rit;
	}
	cout << endl;
	const string s3("hello xzy");
	string::const_iterator cit = s3.begin();
	while (cit != s3.end())
	{
		//*cit += 2; s3不能修改
		cout << *cit << " ";
		++cit;
	}
	cout << endl;
	const string s4("hello xzy");
	string::const_reverse_iterator crit = s4.rbegin();
	while (crit != s4.rend())
	{
		//*crit += 2; s4不能修改
		cout << *crit << " ";
		++crit;
	}
	cout << endl;
	return 0;
}

//在VS2022下的string类
class string
{
private:
	char* _buff[16]; //有效数据小于16，存放在这里
	char* _str;      //有效数据大于等于16，存放在这里
	size_t _size;
	size_t capacity;
};
int main()
{
	string s;
	size_t sz = s.capacity();
	cout << "capacity changed: " << sz << '\n';
	cout << "making s grow:\n";
	for (int i = 0; i < 100; ++i)
	{
		s.push_back('c');
		if (sz != s.capacity())
		{
			sz = s.capacity();
			cout << "capacity changed: " << sz << '\n';
		}
	}
	cout << "VS2022下的string类的大小：" << sizeof(s) << endl;
	return 0;
}

int main()
{
	string s1("hello xzy how are you");
	cout << s1.length() << endl;   //21
	cout << s1.size() << endl;     //21
	cout << s1.max_size() << endl; //2147483647
	cout << s1.capacity() << endl; //31
	string s2("hello xzy how are you");
	s2.reserve(100);//扩容：不一定扩100，但一定大于等于n，取决于编译器，Linux中的g++编译器扩的是100
	cout << s2.empty() << endl;    //0
	cout << s2.capacity() << endl; //111
	s2.shrink_to_fit();            //缩容
	cout << s2.capacity() << endl; //31
	string s3("hello xzy how are you");
	s3.resize(9);
	cout << s3 << endl; //hello xzy
	s3.resize(15, 'w');
	cout << s3 << endl; //hello xzywwwwww
	return 0;
}

int main()
{
	string s1("hello xzy");
	s1.push_back('!');
	cout << s1 << endl; //hello xzy!
	s1.pop_back();
	cout << s1 << endl; //hello xzy
	s1.append(" how are you");
	cout << s1 << endl; //hello xzy! how are you
	//可以用+=取代尾插
	s1 += "???";
	cout << s1 << endl; //hello xzy! how are you???
	string s2("hello xzy!!!");
	string s3;
	s3.assign(s2, 6, 3);
	cout << s3 << endl; //xzy
	string s4("hello xzy");
	s4.insert(0, "hello wj ");
	cout << s4 << endl; //hello wj hello xzy
	string s5("hello xzy!!!");
	s5.erase(9, 2);
	cout << s5 << endl; //hello xzy!
	string s6("hello xzy!!!");
	s6.replace(6, 5, "wj");
	cout << s6 << endl; //hello wj!
	string s7("hello x hello x");
	string tmp;
	tmp.reserve(s7.size());
	for (auto ch : s7)
	{
		if (ch == 'x')
			tmp += "wj";
		else
			tmp += ch;
	}
	cout << tmp << endl; //hello wj hello wj
	s7.swap(tmp);
	cout << s7 << endl;  //hello wj hello wj
	return 0;
}

int main()
{
	string file;
	cin >> file;
	//c_str()函数用于调用C语言的函数，若直接传string，类型不符合（类和指针）
	FILE* fout = fopen(file.c_str(), "r");
	if (fout == NULL)
	{
		perror("open file fail!");
		exit(1);
	}
	char ch = fgetc(fout);
	while (ch != EOF)
	{
		cout << ch;
		ch = fgetc(fout);
	}
	fclose(fout);
	fout = NULL;
	return 0;
}

int main()
{
	//suffix：后缀
	string s1("test.cpp");
	size_t pos1 = s1.find(".");
	string suffix1 = s1.substr(pos1);
	cout << suffix1 << endl; //.cpp
	string s2("test.cpp.zip");
	size_t pos2 = s2.rfind(".");
	string suffix2 = s2.substr(pos2);
	cout << suffix2 << endl; //.zip
	string s3("hello xzy");
	size_t found = s3.find_first_of("xzy");
	while (found != string::npos)
	{
		s3[found] = '*';
		found = s3.find_first_of("xzy", found + 1);
	}
	cout << s3 << endl; //hello ***
	string str1("/user/bin/man");
	cout << endl << str1 << "的路径名与文件名如下：" << endl;
	size_t found1 = str1.find_last_of("/\\");
	cout << "path：" << str1.substr(0, found1) << endl;
	cout << "file：" << str1.substr(found1 + 1) << endl;
	string str2("c:\\windows\\winhelp.exe");
	cout << endl << str2 << "的路径名与文件名如下：" << endl;
	size_t found2 = str2.find_last_of("/\\");
	cout << "path：" << str2.substr(0, found2) << endl;
	cout << "file：" << str2.substr(found2 + 1) << endl;
	return 0;
}

int main()
{
	string s1("hello xzy");
	//1.下标+[]
	for (int i = 0; i < s1.size(); i++)
	{
		s1[i] += 2;//可以修改
		cout << s1[i] << " ";
	}
	cout << endl << s1 << endl;
	return 0;
}

int main()
{
	string s1("hello xzy");
	//2.迭代器
	string::iterator it = s1.begin();
	while (it != s1.end())
	{
		*it += 2;//可以修改
		cout << *it << " ";
		++it;
	}
	cout << endl << s1 << endl;
	return 0;
}

int main()
{
	string s1("hello xzy");
	//3.范围for：字符赋值，自动迭代，自动判断结束
	//  底层就是迭代器
	for (auto ch : s1)
	{
		ch += 2;//修改ch对于s1无影响，ch是它的拷贝
		cout << ch << ' ';
	}
	cout << endl << s1 << endl;
	return 0;
}

int main()
{
	string s1("hello xzy");
	for (auto& ch : s1)//引用：取别名，就可以修改s1
	{
		ch += 2;
		cout << ch << ' ';
	}
	cout << endl << s1 << endl;
	return 0;
}

#include<map>
//auto不能做参数
//void func1(auto a) error
//{}
//auto可以做返回值，但是建议谨慎使用
auto func2()
{
	return 2;
}
int main()
{
	int a = 10;
	auto b = a;//编译期间自动推导类型
	auto c = 'a';
	auto d = func2();
	//auto e; auto必须初始化，否则不知道开多少空间
	int x = 10;
	auto y = &x;
	auto* z = &x;//可以不写*
	auto& m = x;//必须加上&
	auto aa = 1, bb = 2;//right
	//auto cc = 3, dd = 4.0; error必须始终推导为同一类型
	//auto array[] = { 4, 5, 6 }; error数组不能具有其中包含“auto”的元素类型
	// auto 的价值
	map<string, string> dict; //初始化二叉树
	//map<string, string>::iterator mit = dict.begin();
	auto mit = dict.begin();
	cout << typeid(mit).name() << endl;
	return 0;
}

int main()
{
	int array[] = { 1, 2, 3, 4, 5 };
	//范围for适用于《容器》和《数组》
	// C++98的遍历
	for (int i = 0; i < sizeof(array) / sizeof(array[0]); i++)
	{
		cout << array[i] << ' ';
	}
	cout << endl;
	// C++11的遍历
	for (auto& i : array)
	{
		cout << i << ' ';
	}
	cout << endl;
	return 0;
}

#include <iostream>
#include<string>
using namespace std;
int main() 
{
    string str;
    getline(cin, str);
    size_t pos = str.rfind(' ');
    string sub = str.substr(pos + 1);
    cout << sub.size() << endl;
}