一、string类对象的常见构造

#include<iostream>
using namespace std;
#include<string>
//typedef basic_string<char16_t> u16string;std::string s0("Initial string");//构造空的string类对象，即空字符串(默认构造)
//default (1)	explicit basic_string(const allocator_type& alloc = allocator_type());
std::string s1;//用C-string来构造string类对象
//copy(2)    basic_string(const basic_string& str);
std::string s2(s0);//拷贝构造函数
//copy(2)    basic_string(const basic_string& str);
std::string s2(s0);void Teststring()
{string s1;//构造空的string类对象s1string s2("hello sunlang");//用C格式字符串构造string类对象s2string s3(s2);//拷贝构造s3
}

二、string类对象的容量操作

//返回字符串有效字符长度
//size_type size() const;
int main()
{std::string str("Test string");std::cout << "The size of str is" << str.size() << "characters.\n";return 0;
}

//检测字符串释放为空串，是返回true，否则返回false
//bool empty() const;
int main()
{std::string content;std::string line;std::cout << "Please introduce a text.Enter an empty line to finish:\n";do{getline(std::cin, line);content += line + '\n';} while (!line.empty());std::cout << "The text you introduced was:\n" << content;return 0;
}

//清空有效字符
//void clear();
int main()
{char c;std::string str;std::cout << "Please type some lines of text. Enter a dot (.) to finish:\n";do {c = std::cin.get();str += c;if (c == '\n'){std::cout << str;str.clear();}} while (c != '.');return 0;
}

//为字符串预留空间**
//void reserve (size_type n = 0);
int main()
{std::string str;std::ifstream file("test.txt", std::ios::in | std::ios::ate);if (file) {std::ifstream::streampos filesize = file.tellg();str.reserve(filesize);file.seekg(0);while (!file.eof()){str += file.get();}std::cout << str;}return 0;
}

//将有效字符的个数改成n个，多出的空间用字符C填充
//void resize (size_type n);
//void resize(size_type n, charT c)
int main()
{std::string str("I like to code in C");std::cout << str << '\n';std::string::size_type sz = str.size();str.resize(sz + 2, '+');std::cout << str << '\n';str.resize(14);std::cout << str << '\n';return 0;
}

三、类对象的访问及遍历操作

//返回pos位置的字符，const string类对象调用
//reference operator[] (size_type pos);
//const_reference operator[] (size_type pos) const;
int main()
{std::string str("Test string");for (int i = 0; i < str.length(); ++i){std::cout << str[i];}return 0;
}

四、string类对象的修改操作

//在字符串后面追加字符串str
//string(1)
//basic_string& operator+= (const basic_string& str);
//c - string(2)
//basic_string & operator+= (const charT * s);
//character(3)
//basic_string& operator+= (charT c);
int main()
{std::string name("John");std::string family("Smith");name += "K";         // c-stringname += family;         // stringname += '\n';           // characterstd::cout << name;return 0;
}

//返回C格式字符串
//const charT* c_str() const;
int main()
{std::string str("Please split this sentence into tokens");char* cstr = new char[str.length() + 1];std::strcpy(cstr, str.c_str());// cstr now contains a c-string copy of strchar* p = std::strtok(cstr, " ");while (p != 0){std::cout << p << '\n';p = strtok(NULL, " ");}delete[] cstr;return 0;
}

//从字符串pos位置开始往后找字符C，返回该字符在字符串中的位置
//string(1)
//size_type find(const basic_string& str, size_type pos = 0) const;
//c - string(2)
//size_type find(const charT * s, size_type pos = 0) const;
//buffer(3)
//size_type find(const charT* s, size_type pos, size_type n) const;
//character(4)
//size_type find(charT c, size_type pos = 0) const;
int main()
{std::string str("There are two needles in this haystack with needles.");std::string str2("needle");// different member versions of find in the same order as above:std::string::size_type found = str.find(str2);if (found != std::string::npos)std::cout << "first 'needle' found at: " << found << '\n';found = str.find("needles are small", found + 1, 6);if (found != std::string::npos)std::cout << "second 'needle' found at: " << found << '\n';found = str.find("haystack");if (found != std::string::npos)std::cout << "'haystack' also found at: " << found << '\n';found = str.find('.');if (found != std::string::npos)std::cout << "Period found at: " << found << '\n';// let's replace the first needle:str.replace(str.find(str2), str2.length(), "preposition");std::cout << str << '\n';return 0;
}

五、string类非成员函数

//输入运算符重载
//template <class charT, class traits, class Alloc>
//basic_istream<charT, traits>& operator>> (basic_istream<charT, traits>& is,
//	basic_string<charT, traits, Alloc>& str);
int main()
{std::string name;std::cout << "Please, enter your name: ";std::cin >> name;std::cout << "Hello, " << name << "!\n";return 0;
}

//输出运算符重载
//template <class charT, class traits, class Alloc>
//basic_ostream<charT, traits>& operator<< (basic_ostream<charT, traits>& os,
//	const basic_string<charT, traits, Alloc>& str);
int main()
{std::string str = "Hello world!";std::cout << str << '\n';return 0;
}

//获取一行字符串
//template <class charT, class traits, class Alloc>
//（1）basic_istream<charT, traits>& getline(basic_istream<charT, traits>& is,
//	basic_string<charT, traits, Alloc>& str, charT delim);
//(2)
//template <class charT, class traits, class Alloc>
//basic_istream<charT, traits>& getline(basic_istream<charT, traits>& is,
//	basic_string<charT, traits, Alloc>& str);
int main()
{std::string name;std::cout << "Please, enter your full name: ";std::getline(std::cin, name);std::cout << "Hello, " << name << "!\n";return 0;
}

//大小比较
int main()
{std::string foo = "alpha";std::string bar = "beta";if (foo == bar) std::cout << "foo and bar are equal\n";if (foo != bar) std::cout << "foo and bar are not equal\n";if (foo < bar) std::cout << "foo is less than bar\n";if (foo > bar) std::cout << "foo is greater than bar\n";if (foo <= bar) std::cout << "foo is less than or equal to bar\n";if (foo >= bar) std::cout << "foo is greater than or equal to bar\n";return 0;
}

六、汇总代码

#include<iostream>
using namespace std;
#include<string>
//测试string容量相关的接口
//size/clear/resize
void Teststring1()
{//注意：string类对象支持直接用cin和cout进行输入和输出string s("hello,sunlang!!!");//用C-siring来构造string类对象cout << s.size() << endl;//返回字符串有效字符长度cout << s.length() << endl;//返回字符串有效字符长度cout << s.capacity() << endl;//返回空间总大小cout << s << endl;//将s中的字符串清空，注意清空时只是将size清0，不改变底层空间的大小s.clear();cout << s.size() << endl;cout << s.capacity() << endl;//将s中有效字符个数增加到10个，多出位置用‘a'进行补充//"aaaaaaaa"s.resize(10, 'a');cout << s.size() << endl;cout << s << endl;cout << s.capacity() << endl;//将s中有效字符个数增加到15个，多出位置用缺省值'\0'进行补充//"aaaaaaaa\0\0\0\0"s.resize(15);cout << s.size() << endl;cout << s.capacity() << endl;cout << s << endl;//将s中有效字符个数缩小到5个s.resize(5);cout << s.size() << endl;cout << s.capacity() << endl;cout << s << endl;
}
void Teststring2()
{string s;//测试reserve是否会改变string中有效元素个数s.reserve(100);cout << s.size() << endl;cout << s.capacity() << endl;//测试reserve参数小于string的底层空间大小时，是否会将空间缩小s.reserve(50);cout << s.size() << endl;cout<<s.capacity()<<endl;
}
//利用reserve提高插入数据的效率，避免增容带来的开销
void TestPushBack()
{string s;size_t sz = s.capacity();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';}}
}
//构建vector时，如果提前已经知道string中大概要放多少个元素，可以提前将string中空间设置好
void TestPushBackReserve()
{string s;s.reserve(100);size_t sz = s.capacity();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';}}}
//string的遍历
//begin()+end()   for+[]   范围for
//注意：string遍历时使用最多的还是for+下标或者范围for(C++11后才支持)
//begin()+end()大多数使用在需要使用STL提供的算法操作string时，比如：采用reserve逆置string
void Teststring3()
{string s1("hello sunlang");const string s2("Hello sunlang");cout << s1 << " " << s2 << endl;cout << s1[0] << " " << s2[0] << endl;s1[0] = 'H';cout << s1 << endl;//s2[0]='h';代码编译失败，因为const类型对象不能修改
}
void Teststring4()
{string s("hello sunlang");//以下三种方式除了遍历string对象，还可以遍历修改string中的字符//第一种使用最多//for+operator[]for (size_t i = 0; i < s.size(); ++i){cout << s[i] << endl;}//迭代器string::iterator it = s.begin();while (it != s.end()){cout << *it << endl;++it;}//string::reserve_iterator rit =s.rbegin();//C++11之后，直接使用auto定义迭代器，让编译器推到迭代器的类型//auto rit = s.rbegin();//while (rit != s.rend())//{//	cout << *rit << endl;//}//范围forfor (auto ch : s){cout << ch << endl;}
}
//测试string
//1、插入（拼接）方式：push_back append operator+=
//2、正向和反向查找：find()+rfind()
//3、截取子串：substr()
//4、删除：erase
void Teststring5()
{string str;str.push_back(' ');//在str后插入空格str.append("hello");//在str后追加一个字符"hello"str += 's';//在str后追加一个字符'b'str += "un";//在str后追加一个字符串"it"cout << str << endl;cout << str.c_str() << endl;//以C语言的方式打印字符串//获取file的后缀string file("Test.cpp");size_t pos = file.rfind('.');string suffix(file.substr(pos, file.size() - pos));cout << suffix << endl;//npos是string里面的一个静态成员变量//static const size_t npos=-1;//取出ur1中的域名string ur1("https://mp.csdn.net/mp_blog/creation/editor/128085730");cout << ur1 << endl;size_t start = ur1.find("://");if (start == string::npos){cout << "invalid url" << endl;return;}start += 3;size_t finish = url.find('/', start);string address = url.substr(start, finish - start);cout << address << endl;// 删除 url 的协议前缀pos = url.find("://");url.erase(0, pos + 3);cout << url << endl;
}
int main()
{Teststring1();Teststring2();TestPushBack();TestPushBackReserve();Teststring3();Teststring4();Teststring5();return 0;
}