• string类的常用接口说明

    STL六大组件：

    容器 

    算法

    配接器

    迭代器

    仿函数

    空间配置器

    温馨提示：只讲常用接口，使用方法说明详见代码注释

    目录

    一、string类对象的常见构造

    二、string类对象的容量操作

    三、类对象的访问及遍历操作

    四、string类对象的修改操作

    五、string类非成员函数

    六、汇总代码

    一、string类对象的常见构造

    1. #include<iostream>
    2. using namespace std;
    3. #include<string>
    4. //typedef basic_string<char16_t> u16string;
    5.  
    6. std::string s0("Initial string");
    7.  
    8. //构造空的string类对象，即空字符串(默认构造)
    9. //default (1)	explicit basic_string(const allocator_type& alloc = allocator_type());
    10. std::string s1;
    11.  
    12. //用C-string来构造string类对象
    13. //copy(2)    basic_string(const basic_string& str);
    14. std::string s2(s0);
    15.  
    16. //拷贝构造函数
    17. //copy(2)    basic_string(const basic_string& str);
    18. std::string s2(s0);
    19.  
    20. void Teststring()
    21. {
    22. 	string s1;//构造空的string类对象s1
    23. 	string s2("hello sunlang");//用C格式字符串构造string类对象s2
    24. 	string s3(s2);//拷贝构造s3
    25. }

    二、string类对象的容量操作

    1. //返回字符串有效字符长度
    2. //size_type size() const;
    3. int main()
    4. {
    5. 	std::string str("Test string");
    6. 	std::cout << "The size of str is" << str.size() << "characters.\n";
    7. 	return 0;
    8. }
    1. //检测字符串释放为空串，是返回true，否则返回false
    2. //bool empty() const;
    3. int main()
    4. {
    5. 	std::string content;
    6. 	std::string line;
    7. 	std::cout << "Please introduce a text.Enter an empty line to finish:\n";
    8. 	do
    9. 	{
    10. 		getline(std::cin, line);
    11. 		content += line + '\n';
    12. 	} while (!line.empty());
    13. 	std::cout << "The text you introduced was:\n" << content;
    14. 	return 0;
    15. }
    1. //清空有效字符
    2. //void clear();
    3. int main()
    4. {
    5.     char c;
    6.     std::string str;
    7.     std::cout << "Please type some lines of text. Enter a dot (.) to finish:\n";
    8.     do {
    9.         c = std::cin.get();
    10.         str += c;
    11.         if (c == '\n')
    12.         {
    13.             std::cout << str;
    14.             str.clear();
    15.         }
    16.     } while (c != '.');
    17.     return 0;
    18. }
    1. //为字符串预留空间**
    2. //void reserve (size_type n = 0);
    3. int main()
    4. {
    5.     std::string str;
    6.  
    7.     std::ifstream file("test.txt", std::ios::in | std::ios::ate);
    8.     if (file) {
    9.         std::ifstream::streampos filesize = file.tellg();
    10.         str.reserve(filesize);
    11.  
    12.         file.seekg(0);
    13.         while (!file.eof())
    14.         {
    15.             str += file.get();
    16.         }
    17.         std::cout << str;
    18.     }
    19.     return 0;
    20. }
    1. //将有效字符的个数改成n个，多出的空间用字符C填充
    2. //void resize (size_type n);
    3. //void resize(size_type n, charT c)
    4. int main()
    5. {
    6. 	std::string str("I like to code in C");
    7. 	std::cout << str << '\n';
    8.  
    9. 	std::string::size_type sz = str.size();
    10.  
    11. 	str.resize(sz + 2, '+');
    12. 	std::cout << str << '\n';
    13.  
    14. 	str.resize(14);
    15. 	std::cout << str << '\n';
    16. 	return 0;
    17. }

    三、类对象的访问及遍历操作

    1. //返回pos位置的字符，const string类对象调用
    2. //reference operator[] (size_type pos);
    3. //const_reference operator[] (size_type pos) const;
    4. int main()
    5. {
    6. 	std::string str("Test string");
    7. 	for (int i = 0; i < str.length(); ++i)
    8. 	{
    9. 		std::cout << str[i];
    10. 	}
    11. 	return 0;
    12. }

    四、string类对象的修改操作

    1. //在字符串后面追加字符串str
    2. //string(1)
    3. //basic_string& operator+= (const basic_string& str);
    4. //c - string(2)
    5. //basic_string & operator+= (const charT * s);
    6. //character(3)
    7. //basic_string& operator+= (charT c);
    8. int main()
    9. {
    10. 	std::string name("John");
    11. 	std::string family("Smith");
    12. 	name += "K";         // c-string
    13. 	name += family;         // string
    14. 	name += '\n';           // character
    15.  
    16. 	std::cout << name;
    17. 	return 0;
    18. }
    1. //返回C格式字符串
    2. //const charT* c_str() const;
    3. int main()
    4. {
    5. 	std::string str("Please split this sentence into tokens");
    6.  
    7. 	char* cstr = new char[str.length() + 1];
    8. 	std::strcpy(cstr, str.c_str());
    9.  
    10. 	// cstr now contains a c-string copy of str
    11.  
    12. 	char* p = std::strtok(cstr, " ");
    13. 	while (p != 0)
    14. 	{
    15. 		std::cout << p << '\n';
    16. 		p = strtok(NULL, " ");
    17. 	}
    18.  
    19. 	delete[] cstr;
    20. 	return 0;
    21. }
    1. //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
    2. //string(1)
    3. //size_type find(const basic_string& str, size_type pos = 0) const;
    4. //c - string(2)
    5. //size_type find(const charT * s, size_type pos = 0) const;
    6. //buffer(3)
    7. //size_type find(const charT* s, size_type pos, size_type n) const;
    8. //character(4)
    9. //size_type find(charT c, size_type pos = 0) const;
    10. int main()
    11. {
    12.     std::string str("There are two needles in this haystack with needles.");
    13.     std::string str2("needle");
    14.  
    15.     // different member versions of find in the same order as above:
    16.     std::string::size_type found = str.find(str2);
    17.     if (found != std::string::npos)
    18.         std::cout << "first 'needle' found at: " << found << '\n';
    19.  
    20.     found = str.find("needles are small", found + 1, 6);
    21.     if (found != std::string::npos)
    22.         std::cout << "second 'needle' found at: " << found << '\n';
    23.  
    24.     found = str.find("haystack");
    25.     if (found != std::string::npos)
    26.         std::cout << "'haystack' also found at: " << found << '\n';
    27.  
    28.     found = str.find('.');
    29.     if (found != std::string::npos)
    30.         std::cout << "Period found at: " << found << '\n';
    31.  
    32.     // let's replace the first needle:
    33.     str.replace(str.find(str2), str2.length(), "preposition");
    34.     std::cout << str << '\n';
    36.     return 0;
    37. }

    五、string类非成员函数

    1. //输入运算符重载
    2. //template <class charT, class traits, class Alloc>
    3. //basic_istream<charT, traits>& operator>> (basic_istream& is,
    4. //	basic_string<charT, traits, Alloc>& str);
    5. int main()
    6. {
    7. 	std::string name;
    8.  
    9. 	std::cout << "Please, enter your name: ";
    10. 	std::cin >> name;
    11. 	std::cout << "Hello, " << name << "!\n";
    12.  
    13. 	return 0;
    14. }
    1. //输出运算符重载
    2. //template <class charT, class traits, class Alloc>
    3. //basic_ostream<charT, traits>& operator<< (basic_ostream<charT, traits>& os,
    4. //	const basic_string<charT, traits, Alloc>& str);
    5. int main()
    6. {
    7. 	std::string str = "Hello world!";
    8. 	std::cout << str << '\n';
    9. 	return 0;
    10. }
    1. //获取一行字符串
    2. //template <class charT, class traits, class Alloc>
    3. //（1）basic_istream<charT, traits>& getline(basic_istream<charT, traits>& is,
    4. //	basic_string<charT, traits, Alloc>& str, charT delim);
    5. //(2)
    6. //template <class charT, class traits, class Alloc>
    7. //basic_istream<charT, traits>& getline(basic_istream<charT, traits>& is,
    8. //	basic_string<charT, traits, Alloc>& str);
    9. int main()
    10. {
    11. 	std::string name;
    12.  
    13. 	std::cout << "Please, enter your full name: ";
    14. 	std::getline(std::cin, name);
    15. 	std::cout << "Hello, " << name << "!\n";
    16.  
    17. 	return 0;
    18. }
    1. //大小比较
    2. int main()
    3. {
    4. 	std::string foo = "alpha";
    5. 	std::string bar = "beta";
    6.  
    7. 	if (foo == bar) std::cout << "foo and bar are equal\n";
    8. 	if (foo != bar) std::cout << "foo and bar are not equal\n";
    9. 	if (foo < bar) std::cout << "foo is less than bar\n";
    10. 	if (foo > bar) std::cout << "foo is greater than bar\n";
    11. 	if (foo <= bar) std::cout << "foo is less than or equal to bar\n";
    12. 	if (foo >= bar) std::cout << "foo is greater than or equal to bar\n";
    13.  
    14. 	return 0;
    15. }

    六、汇总代码

    1. #include
    2. using namespace std;
    3. #include
    4. //测试string容量相关的接口
    5. //size/clear/resize
    6. void Teststring1()
    7. {
    8. 	//注意：string类对象支持直接用cin和cout进行输入和输出
    9. 	string s("hello,sunlang!!!");//用C-siring来构造string类对象
    10. 	cout << s.size() << endl;//返回字符串有效字符长度
    11. 	cout << s.length() << endl;//返回字符串有效字符长度
    12. 	cout << s.capacity() << endl;//返回空间总大小
    13. 	cout << s << endl;
    14. 	//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
    15. 	s.clear();
    16. 	cout << s.size() << endl;
    17. 	cout << s.capacity() << endl;
    18. 	//将s中有效字符个数增加到10个，多出位置用‘a'进行补充
    19. 	//"aaaaaaaa"
    20. 	s.resize(10, 'a');
    21. 	cout << s.size() << endl;
    22. 	cout << s << endl;
    23. 	cout << s.capacity() << endl;
    24. 	//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
    25. 	//"aaaaaaaa\0\0\0\0"
    26. 	s.resize(15);
    27. 	cout << s.size() << endl;
    28. 	cout << s.capacity() << endl;
    29. 	cout << s << endl;
    30. 	//将s中有效字符个数缩小到5个
    31. 	s.resize(5);
    32. 	cout << s.size() << endl;
    33. 	cout << s.capacity() << endl;
    34. 	cout << s << endl;
    35. }
    36. void Teststring2()
    37. {
    38. 	string s;
    39. 	//测试reserve是否会改变string中有效元素个数
    40. 	s.reserve(100);
    41. 	cout << s.size() << endl;
    42. 	cout << s.capacity() << endl;
    43. 	//测试reserve参数小于string的底层空间大小时，是否会将空间缩小
    44. 	s.reserve(50);
    45. 	cout << s.size() << endl;
    46. 	cout<capacity()<
    47. }
    48. //利用reserve提高插入数据的效率，避免增容带来的开销
    49. void TestPushBack()
    50. {
    51. 	string s;
    52. 	size_t sz = s.capacity();
    53. 	cout << "making s grow:\n";
    54. 	for (int i = 0; i < 100; ++i)
    55. 	{
    56. 		s.push_back('c');
    57. 		if (sz != s.capacity())
    58. 		{
    59. 			sz = s.capacity();
    60. 			cout << "capacity changed:" << sz << '\n';
    61. 		}
    62. 	}
    63. }
    64. //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
    65. void TestPushBackReserve()
    66. {
    67. 	string s;
    68. 	s.reserve(100);
    69. 	size_t sz = s.capacity();
    70. 	cout << "making s grow:\n";
    71. 	for (int i = 0; i < 100; ++i)
    72. 	{
    73. 		s.push_back('c');
    74. 		if (sz != s.capacity())
    75. 		{
    76. 			sz = s.capacity();
    77. 			cout << "capacity changed:" << sz << '\n';
    78. 		}
    79. 	}
    80.  
    81. }
    82. //string的遍历
    83. //begin()+end()   for+[]   范围for
    84. //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)
    85. //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
    86. void Teststring3()
    87. {
    88. 	string s1("hello sunlang");
    89. 	const string s2("Hello sunlang");
    90. 	cout << s1 << " " << s2 << endl;
    91. 	cout << s1[0] << " " << s2[0] << endl;
    92. 	
    93. 	s1[0] = 'H';
    94. 	cout << s1 << endl;
    95. 	//s2[0]='h';代码编译失败，因为const类型对象不能修改
    96. }
    97. void Teststring4()
    98. {
    99. 	string s("hello sunlang");
    100. 	//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
    101. 	//第一种使用最多
    102. 	//for+operator[]
    103. 	for (size_t i = 0; i < s.size(); ++i)
    104. 	{
    105. 		cout << s[i] << endl;
    106. 	}
    107. 	//迭代器
    108. 	string::iterator it = s.begin();
    109. 	while (it != s.end())
    110. 	{
    111. 		cout << *it << endl;
    112. 		++it;
    113. 	}
    114. 	//string::reserve_iterator rit =s.rbegin();
    115. 	//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
    116. 	//auto rit = s.rbegin();
    117. 	//while (rit != s.rend())
    118. 	//{
    119. 	//	cout << *rit << endl;
    120. 	//}
    121. 	//范围for
    122. 	for (auto ch : s)
    123. 	{
    124. 		cout << ch << endl;
    125. 	}
    126. }
    127. //测试string
    128. //1、插入（拼接）方式：push_back append operator+=
    129. //2、正向和反向查找：find()+rfind()
    130. //3、截取子串：substr()
    131. //4、删除：erase
    132. void Teststring5()
    133. {
    134. 	string str;
    135. 	str.push_back(' ');//在str后插入空格
    136. 	str.append("hello");//在str后追加一个字符"hello"
    137. 	str += 's';//在str后追加一个字符'b'
    138. 	str += "un";//在str后追加一个字符串"it"
    139. 	cout << str << endl;
    140. 	cout << str.c_str() << endl;//以C语言的方式打印字符串
    141. 	//获取file的后缀
    142. 	string file("Test.cpp");
    143. 	size_t pos = file.rfind('.');
    144. 	string suffix(file.substr(pos, file.size() - pos));
    145. 	cout << suffix << endl;
    146. 	//npos是string里面的一个静态成员变量
    147. 	//static const size_t npos=-1;
    148. 	//取出ur1中的域名
    149. 	string ur1("https://mp.csdn.net/mp_blog/creation/editor/128085730");
    150. 	cout << ur1 << endl;
    151. 	size_t start = ur1.find("://");
    152. 	if (start == string::npos)
    153. 	{
    154. 		cout << "invalid url" << endl;
    155. 		return;
    156. 	}
    157. 	start += 3;
    158. 	size_t finish = url.find('/', start);
    159. 	string address = url.substr(start, finish - start);
    160. 	cout << address << endl;
    161. 	// 删除 url 的协议前缀
    162. 	pos = url.find("://");
    163. 	url.erase(0, pos + 3);
    164. 	cout << url << endl;
    165. }
    166. int main()
    167. {
    168. 	Teststring1();
    169. 	Teststring2();
    170. 	TestPushBack();
    171. 	TestPushBackReserve();
    172. 	Teststring3();
    173. 	Teststring4();
    174. 	Teststring5();
    175. 	return 0;
    176. }

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  • 原文地址：https://blog.csdn.net/lang_965/article/details/128085730