C++/C++11中std::string用法汇总

C++/C++11中std::string是个模板类，它是一个标准库。使用string类型必须首先包含<string>头文件。作为标准库的一部分，string定义在命名空间std中。

std::string是C++中的字符串。字符串对象是一种特殊类型的容器，专门设计来操作字符序列。

strings are objects that represent sequences of characters.

The standard string class provides support for such objects with an interface similar to that of a standard container of bytes, but adding features specifically designed to operate with strings of single-byte characters.

The string class is an instantiation of the basic_string class template that uses char (i.e.,bytes) as its character type, with its default char_traits and allocator types.

Note that this class handles bytes independently of the encoding used: If used to handle sequences of multi-byte or variable-length characters (such as UTF-8),all members of this class (such as length or size), as well as its iterators,will still operate in terms of bytes (not actual encoded characters).

一个容器就是一些特定类型对象的集合。顺序容器(sequential container)为程序员提供了控制元素存储和访问顺序的能力。这种顺序不依赖于元素的值，而是与元素加入容器时的位置相对应。

标准库中的顺序容器包括：

(1)、vector：可变大小数组。支持快速随机访问。在尾部之外的位置插入或删除元素可能很慢。

(2)、deque：双端队列。支持快速随机访问。在头尾位置插入/删除速度很快。

(3)、list：双向链表。只支持双向顺序访问。在list中任何位置进行插入/删除操作速度都很快。

(4)、forward_list：单向链表。只支持单向顺序访问。在链表任何位置进行插入/删除操作速度都很快。

(5)、array：固定大小数组。支持快速随机访问。不能添加或删除元素。

(6)、string：与vector相似的容器，但专门用于保存字符。随机访问快。在尾部插入/删除速度快。

除了固定大小的array外，其它容器都提供高效、灵活的内存管理。我们可以添加和删除元素，扩张和收缩容器的大小。容器保存元素的策略对容器操作的效率有着固定的，有时是重大的影响。在某些情况下，存储策略还会影响特定容器是否支持特定操作。

例如，string和vector将元素保存在连续的内存空间中。由于元素是连续存储的，由元素的下标来计算其地址是非常快速的。但是，在这两种容器的中间位置添加或删除元素就会非常耗时：在一次插入或删除操作后，需要移动插入/删除位置之后的所有元素，来保持连续存储。而且，添加一个元素有时可能还需要分配额外的存储空间。在这种情况下，每个元素都必须移动到新的存储空间中。

list和forward_list两个容器的设计目的是令容器任何位置的添加和删除操作都很快速。作为代价，这两个容器不支持元素的随机访问：为了访问一个元素，我们只能遍历整个容器。而且，与vector、deque和array相比，这两个容器的额外内存开销也很大。

deque是一个更为复杂的数据结构。与string和vector类似，deque支持快速的随机访问。与string和vector一样，在deque的中间位置添加或删除元素的代价(可能)很高。但是，在deque的两端添加或删除元素都是很快的，与list或forward_list添加删除元素的速度相当。

forward_list和array是新C++标准增加的类型。与内置数组相比，array是一个种更安全、更容易使用的数组类型。与内置数组类似，array对象的大小是固定的。因此，array不支持添加和删除元素以及改变容器大小的操作。forward_list的设计目标是达到与最好的手写的单向链表数据结构相当的性能。因此，forward_list没有size操作，因为保存或计算其大小就会比手写链表多出额外的开销。对其他容器而言，size保证是一个快速的常量时间的操作。

通常，使用vector是最好的选择，除法你有很好的理由选择其他容器。

以下是一些选择容器的基本原则：

(1)、除法你有很好的理由选择其他容器，否则应该使用vector；

(2)、如果你的程序有很多小的元素，且空间的额外开销很重要，则不要使用list或forward_list；

(3)、如果程序要求随机访问元素，应使用vector或deque；

(4)、如果程序要求在容器的中间插入或删除元素，应使用list或forward_list；

(5)、如果程序需要在头尾位置插入或删除元素，但不会在中间位置进行插入或删除操作，则使用deque；

(6)、如果程序只有在读取输入时才需要在容器中间位置插入元素，随后需要随机访问元素，则：首先，确定是否真的需要在容器中间位置添加元素。当处理输入数据时，通常可以很容器地向vector追加数据，然后再调用标准库的sort函数来重排容器中的元素，从而避免在中间位置添加元素。如果必须在中间位置插入元素，考虑在输入阶段使用list，一旦输入完成，将list中的内容拷贝到一个vector中。

如果你不确定应该使用哪种容器，那么可以在程序中只使用vector和list公共的操作：使用迭代器，不使用下标操作，避免随机访问。这样，在必要时选择使用vector或list都很方便。

一般来说，每个容器都定义在一个头文件中，文件名与类型名相同。即，deque定义在头文件deque中，list定义在头文件list中，以此类推。容器均定义为模板类。

顺序容器几乎可以保存任意类型的元素。特别是，我们可以定义一个容器，其元素的类型是另一个容器。这种容器的定义与任何其他容器类型完全一样：在尖括号中指定元素类型(此种情况下，是另一种容器类型)。

typedef basic_string<char, char_traits<char>, allocator<char> >			string;
typedef basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> >	wstring;
typedef basic_string<char16_t, char_traits<char16_t>, allocator<char16_t> >	u16string;
typedef basic_string<char32_t, char_traits<char32_t>, allocator<char32_t> >	u32string;

下面的测试代码包含了std::string的所有用法，主要来自 http://www.cplusplus.com/reference/string/string/ 和《C++ Primer(Fifth Edition)》：

#include "string.hpp"
#include <string>
#include <iostream>
#include <cctype>
#include <cstddef> // std::size_t
#include <fstream>/*typedef basic_string<char, char_traits<char>, allocator<char> >			string;typedef basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> >	wstring;typedef basic_string<char16_t, char_traits<char16_t>, allocator<char16_t> >	u16string;typedef basic_string<char32_t, char_traits<char32_t>, allocator<char32_t> >	u32string;
*/int test_string_init()
{// 如果使用等号(=)初始化一个变量，实际上执行的是拷贝初始化，编译器把等号右侧的初始化拷贝到新创建的对象中去。// 与之相反，如果不使用等号，则执行的是直接初始化std::string s1; // 默认初始化，s1是一个空串std::string s2(s1); // s2是s1的副本std::string s3 = s1; // 等价于s3(s1)，s3是s1的副本std::string s4("value"); // s4是字面值"value"的副本，除了字面值最后的那个空字符外，直接初始化std::string s5 = "value"; // 等价于s5("value"),s5是字面值"value"的副本,拷贝初始化std::string s6(10, 'c'); // 把s6初始化为由连续10个字符c组成的串，直接初始化// 对于用多个值进行初始化的情况，非要用拷贝初始化的方式来处理也不是不可以，// 不过需要显示地创建一个(临时)对象用于拷贝std::string s7 = std::string(10, 'c'); // 拷贝初始化，等价于： std::string tmp(10, 'c'); std::string s7 = tmp;// string s(s2, pos2) : s是string s2从下标pos2开始的字符的拷贝，若pos2>s2.size()，构造函数的行为未定义std::string s8(s4, 2);// string s(cp, n) : s是cp指向的数组中前n个字符的拷贝，此数组至少应该包含n个字符char cp[6] {"abcde"};std::string s9(cp, 2);// string s(s2, pos2, len2) : s是string s2从下标pos2开始len2个字符的拷贝。若pos2>s2.size(),构造函数的行为未定义.// 不管len2的值是多少，构造函数至多拷贝s2.size()-pos2个字符std::string s10(s4, 1, 2);return 0;
}int test_string_base()
{int num{ 0 };std::cin >> num;switch (num) {case 0: {// 读写string对象std::string s1;std::cin >> s1; // 将string对象读入s1,遇到空白停止, string对象会自动忽然开头的空白(即空格符、换行符、制表符等)// 并从第一个真正的字符开始读起，直到遇见下一个空白为止std::cout << s1 << std::endl; // 输出s1;std::string s2, s3;std::cin >> s2 >> s3; // 多个输入或多个输出可以连写在一起std::cout << s2 << s3 << std::endl;}break;case 1: {// 读取未知数量的string对象std::string s4;while (std::cin >> s4) { // 反复读取，直至到达文件末尾(ctrl+z)std::cout << s4 << std::endl; // 逐个输出单词，每个单词后面紧跟一个换行}}break;case 2: {// 使用getline读取一整行,getline只要一遇到换行符就结束读取操作并返回结果std::string s5;while (std::getline(std::cin, s5)) { // 按ctrl+z退出循环std::cout << s5 << std::endl; // 触发getline函数返回的那个换行符实际上被丢弃掉了，// 得到的string对象中并不包含该换行符}}break;case 3: {// empty：是否为空返回一个对应的布尔值// 每次读入一整行，遇到空行直接跳过std::string s6;while (std::getline(std::cin, s6)) {if (!s6.empty())std::cout << s6 << std::endl;elsestd::cout << "it is empty" << std::endl;}}break;case 4: {// size： 返回string对象的长度(即string对象中字符的个数)std::string s7;while (std::getline(std::cin, s7)) {auto len = s7.size(); // size函数返回的是一个std::string::size_type类型的值，// 它是一个无符号类型的值，而且能足够存放下任何string对象的大小,std::cout << "string size: " << len << std::endl;}}break;case 5: {// 比较string对象：大小写敏感：==、!=、<、<=、>、>=std::string s1{ "hello" }, s2{ "Hello" }, s3{"Hello world"};if (s1 > s2)std::cout << "s1 > s2" << std::endl;else if (s1 == s2)std::cout << "s1 == s2" << std::endl;else if (s1 < s2)std::cout << "s1 < s2" << std::endl;if (s2 <= s3)std::cout << "s2 <= s3" << std::endl;}break;case 6: {// +: 其内容是把左侧的运算对象与右侧的运算对象串接std::string s1{ "hello, " }, s2{ "world" }, s3;s3 = s1 + s2;std::cout << "s3: " << s3 << std::endl;// 当把string对象和字符字面值及字符串字面值混在一条语句中使用时，// 必须确保每个加法运算符(+)的两侧的对象至少有一个是string,// 不能把字面值直接相加// Note: 字符串字面值与string是不同的类型std::string s4{ "csdn blog" }, s5{ "http://blog.csdn.net/" }, s6;s6 = s4 + ": " + s5 + "fengbingchun";std::cout << s6 << std::endl;}break;case 7: {// substr: 返回一个string，它是原始string的一部分或全部的拷贝,// 可以传递给substr一个可选的开始位置和计数值std::string s{ "hello world" };std::string s2 = s.substr(0, 5); // s2 = hellostd::string s3 = s.substr(6); // s3 = worldstd::string s4 = s.substr(6, 11); // s3 = world//std::string s5 = s.substr(12); // 抛出一个out_of_range异常fprintf(stderr, "s2: %s; s3: %s; s4: %s\n", s2.c_str(), s3.c_str(), s4.c_str());// insert、erase、assigns.insert(s.size(), 5, '!'); // 在s末尾插入5个感叹号fprintf(stdout, "s:  %s\n", s.c_str());s.erase(s.size() - 5, 5); // 从s删除最后5个字符fprintf(stdout, "s: %s\n", s.c_str());const char* cp = "Stately, plump Buck";s.assign(cp, 7); // s = "Stately"fprintf(stdout, "s: %s\n", s.c_str());s.insert(s.size(), cp + 7); // s = "Stately, plump Buck"fprintf(stdout, "s: %s\n", s.c_str());std::string s5{ " some string " }, s6{ " some other string " };s5.insert(0, s6); // 在s5中位置0之前插入s6的拷贝fprintf(stdout, "s5: %s\n", s5.c_str());s5.insert(0, s6, 0, s6.size()); // 在s5[0]之前插入s6中s6[0]开始的s6.size()个字符fprintf(stdout, "s5: %s\n", s5.c_str());// append: 是在末尾进行插入操作的一种简写形式std::string s7{ "C++ Primer" }, s8{ s7 };s7.insert(s7.size(), " 5th Ed.");s8.append(" 5th Ed.");fprintf(stdout, "s7: %s; s8: %s\n", s7.c_str(), s8.c_str());// replace: 是调用erase和insert的一种简写形式s7.replace(11, 3, "Fifth"); // s7.erase(11, 3); s7.insert(11, "Fifth");fprintf(stdout, "s7: %s\n", s7.c_str());/*s.find(args)：查找s中args第一次出现的位置s.rfind(args)：查找s中args最后一次出现的位置s.find_first_of(args)：在s中查找args中任何一个字符第一次出现的位置s.find_last_of(args)：在s中查找args中任何一个字符最后一次出现的位置s.find_first_not_of(args)：在s中查找第一个不在args中的字符s.find_last_not_of(args)：在s中查找最后一个不在args中的字符*/// find: 返回第一个匹配位置的下标std::string s9{ "AnnaBelle" };auto pos1 = s9.find("Belle");auto pos2 = s9.find("xxx");fprintf(stdout, "pos1: %d, pos2: %d\n", pos1, pos2); // 4, -1// find_first_of: 查找与给定字符串中任何一个字符匹配的位置std::string numbers{ "0123456789" }, name{ "r2d2" };auto pos3 = name.find_first_of(numbers);fprintf(stdout, "pos3: %d\n", pos3); // 1, name中第一个数字的下标// find_first_not_of: 第一个不在参数中的字符std::string s10{ "03714p3" };auto pos4 = s10.find_first_not_of(numbers);fprintf(stdout, "pos4: %d\n", pos4); // 5// compare: 返回0(等于)、正数(大于)或负数(小于)auto ret = numbers.compare(name);fprintf(stdout, "compare result: %d\n", ret);// -1// 数值数据与string之间的转换int i{ 43 };std::string s11 = std::to_string(i); // 将整数i转换为字符表示形式double d = std::stod(s11); // 将字符串s11转换为浮点数fprintf(stdout, "s11: %s, d: %f\n", s11.c_str(), d);/*to_string(val):一组重载函数，返回数值val的string表示。val可以是任何算术类型stoi(s,p,b)/stol(s,p,b)/stoul(s,p,b)/stoll(s,p,b)/stoull(s,p,b)：返回s的起始子串(表示整数内容)的数值，返回类型分别是int、long、unsigned long、long long、unsigned long long。b表示转换所用的基数，默认值为10.p是size_t指针，用来保存s中第一个非数值字符的下标，p默认是0，即，函数不保存下标。stof(s,p)/stod(s,p)/stold(s,p)：返回s的起始子串(表示浮点数内容)的数值，返回值类型分别是float、double或long double.参数p的作用与整数转换函数中一样。*/}break;default:break;}return 0;
}int test_string_cctype()
{/* include <cctype>isalnum(c)：当c是字母或数字时为真isalpha(c)：当c是字母时为真isblank(c)：当c是空白字符时为真(C++11)iscntrl(c)：当c时控制字符时为真isdigit(c)：当c是数字时为真isgraph(c)：当c不是空格但可打印时为真islower(c)：当c是小写字母时为真isprint(c)：当c是可打印字符时为真(即c是空格或c具有可视形式)ispunct(c)：当c是标点符号时为真(即c不是控制字符、数字、字母、可打印空白中的一种)isspace(c)：当c是空白时为真(即c是空格、横向制表符、纵向制表符、回车符、换行符、进纸符中的一种)isupper(c)：当c是大写字母时为真isxdigit(c)：当c是十六进制数字时为真tolower(c)：如果c是大写字母，输出对应的小写字母；否则原样输出ctoupper(c)：如果c是小写字母，输出对应的大写字母；否则原样输出c*/std::string s1{ "Hello World!!!" };decltype(s1.size()) punct_cnt{ 0 };for (auto c : s1) {if (ispunct(c))++punct_cnt;}std::cout << punct_cnt << " punctutation characters in " << s1 << std::endl;for (auto &c : s1) { // 对于s1中的每个字符(Note:c是引用)c = toupper(c); // c是一个引用，因此赋值语句将改变s中字符的值}std::cout << "toupper s1: " << s1 << std::endl;// string对象的下标必须大于等于0而小于s.size()// Note：C++标准并不要求标准库检测下标是否合法。一旦使用了一个超出范围的下标，就会产生不可预知的结果std::string s2{"some string"};for (decltype(s2.size()) index = 0; index != s2.size() && !isspace(s2[index]); ++index) {s2[index] = toupper(s2[index]);}std::cout << "s2: " << s2 << std::endl;// 使用下标执行随机访问const std::string s3{"0123456789ABCDEF"};std::cout << "Enter a series of numbers between 0 and 15"<< "separated by spaces. Hit ENTER when finished: " << std::endl;std::string result;std::string::size_type n;while (std::cin >> n) {if (n < s3.size())result += s3[n];std::cout << "Your hex number is: " << result << std::endl;}return 0;
}static void SplitFilename(const std::string& str)
{std::cout << "Splitting: " << str << '\n';std::size_t found = str.find_last_of("/\\");std::cout << " path: " << str.substr(0, found) << '\n';std::cout << " file: " << str.substr(found + 1) << '\n';
}int test_string_func()
{// reference: http://www.cplusplus.com/reference/string/string/{ // appendstd::string str;std::string str2 = "Writing ";std::string str3 = "print 10 and then 5 more";// used in the same order as described above:str.append(str2);                       // "Writing "str.append(str3, 6, 3);                   // "10 "str.append("dots are cool", 5);          // "dots "str.append("here: ");                   // "here: "str.append(10u, '.');                    // ".........."str.append(str3.begin() + 8, str3.end());  // " and then 5 more"str.append(5, 0x2E);                // "....."std::cout << str << '\n';}{ // assignstd::string str;std::string base = "The quick brown fox jumps over a lazy dog.";// used in the same order as described above:str.assign(base);std::cout << str << '\n';str.assign(base, 10, 9);std::cout << str << '\n';         // "brown fox"str.assign("pangrams are cool", 7);std::cout << str << '\n';         // "pangram"str.assign("c-string");std::cout << str << '\n';         // "c-string"str.assign(10, '*');std::cout << str << '\n';         // "**********"str.assign(10, 0x2D);std::cout << str << '\n';         // "----------"str.assign(base.begin() + 16, base.end() - 12);std::cout << str << '\n';         // "fox jumps over"
}{ // atstd::string str("Test string");for (unsigned i = 0; i<str.length(); ++i) {std::cout << str.at(i);}std::cout << '\n';}{ // back(c++11)std::string str("hello world.");str.back() = '!';std::cout << str << '\n';}{ // begin/endstd::string str("Test string");for (std::string::iterator it = str.begin(); it != str.end(); ++it)std::cout << *it;std::cout << '\n';}{ // capacitystd::string str("Test string");std::cout << "size: " << str.size() << "\n";std::cout << "length: " << str.length() << "\n";std::cout << "capacity: " << str.capacity() << "\n";std::cout << "max_size: " << str.max_size() << "\n";}{ // cbegin/cend(c++11)std::string str("Lorem ipsum");for (auto it = str.cbegin(); it != str.cend(); ++it)std::cout << *it;std::cout << '\n';}{ // clearchar 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 != '.');}{ // comparestd::string str1("green apple");std::string str2("red apple");if (str1.compare(str2) != 0)std::cout << str1 << " is not " << str2 << '\n';if (str1.compare(6, 5, "apple") == 0)std::cout << "still, " << str1 << " is an apple\n";if (str2.compare(str2.size() - 5, 5, "apple") == 0)std::cout << "and " << str2 << " is also an apple\n";if (str1.compare(6, 5, str2, 4, 5) == 0)std::cout << "therefore, both are apples\n";}{ // copychar buffer[20];std::string str("Test string...");std::size_t length = str.copy(buffer, 6, 5);buffer[length] = '\0';std::cout << "buffer contains: " << buffer << '\n';}{ // crbegin/crend(c++11)std::string str("lorem ipsum");for (auto rit = str.crbegin(); rit != str.crend(); ++rit)std::cout << *rit;std::cout << '\n';}{ // c_strstd::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 = std::strtok(NULL, " ");}delete[] cstr;}{ // dataint length;std::string str = "Test string";char* cstr = "Test string";if (str.length() == std::strlen(cstr)) {std::cout << "str and cstr have the same length.\n";if (memcmp(cstr, str.data(), str.length()) == 0)std::cout << "str and cstr have the same content.\n";}}{ // emptystd::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;}{ // erasestd::string str("This is an example sentence.");std::cout << str << '\n';// "This is an example sentence."str.erase(10, 8);                        //            ^^^^^^^^std::cout << str << '\n';// "This is an sentence."str.erase(str.begin() + 9);               //           ^std::cout << str << '\n';// "This is a sentence."str.erase(str.begin() + 5, str.end() - 9);  //       ^^^^^std::cout << str << '\n';// "This sentence."}{ // findstd::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::size_t 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';}{ // find_first_not_ofstd::string str("look for non-alphabetic characters...");std::size_t found = str.find_first_not_of("abcdefghijklmnopqrstuvwxyz ");if (found != std::string::npos) {std::cout << "The first non-alphabetic character is " << str[found];std::cout << " at position " << found << '\n';}}{ // find_first_ofstd::string str("Please, replace the vowels in this sentence by asterisks.");std::size_t found = str.find_first_of("aeiou");while (found != std::string::npos) {str[found] = '*';found = str.find_first_of("aeiou", found + 1);}std::cout << str << '\n';}{ // find_last_not_ofstd::string str("Please, erase trailing white-spaces   \n");std::string whitespaces(" \t\f\v\n\r");std::size_t found = str.find_last_not_of(whitespaces);if (found != std::string::npos)str.erase(found + 1);elsestr.clear();            // str is all whitespacestd::cout << '[' << str << "]\n";}{ // find_last_ofstd::string str1("/usr/bin/man");std::string str2("c:\\windows\\winhelp.exe");SplitFilename(str1);SplitFilename(str2);}{ // front(c++11)std::string str("test string");str.front() = 'T';std::cout << str << '\n';}{ // get_allocator// reference: http://www.tenouk.com/cpluscodesnippet/cplusbasic_stringget_allocator.html// using the default allocatorstd::string str1 = "1234";std::basic_string <char> str2 = "567ABC";std::basic_string <char, std::char_traits<char>, std::allocator<char> > str3 = "DefauLt";std::cout << "str1 = " << str1 << std::endl;std::cout << "str2 = " << str2 << std::endl;std::cout << "str3 = " << str3 << std::endl;// str4 will use the same allocator class as str1std::basic_string <char> str4(str1.get_allocator());std::basic_string <char>::allocator_type xchar = str1.get_allocator();str4 = "Just a string";std::cout << "str4 = " << str4 << std::endl;if (xchar == str1.get_allocator())std::cout << "The allocator objects xchar and str1.get_allocator() are equal." << std::endl;elsestd::cout << "The allocator objects xchar and str1.get_allocator() are not equal." << std::endl;// you can now call functions on the allocator class xchar used by str1std::string str5(xchar);}{ // insertstd::string str = "to be question";std::string str2 = "the ";std::string str3 = "or not to be";std::string::iterator it;// used in the same order as described above:str.insert(6, str2);                 // to be (the )questionstr.insert(6, str3, 3, 4);             // to be (not )the questionstr.insert(10, "that is cool", 8);    // to be not (that is )the questionstr.insert(10, "to be ");            // to be not (to be )that is the questionstr.insert(15, 1, ':');               // to be not to be(:) that is the questionit = str.insert(str.begin() + 5, ','); // to be(,) not to be: that is the questionstr.insert(str.end(), 3, '.');       // to be, not to be: that is the question(...)str.insert(it + 2, str3.begin(), str3.begin() + 3); // (or )std::cout << str << '\n';}{ // lengthstd::string str("Test string");std::cout << "The size of str is " << str.length() << " bytes.\n";}{ // max_sizestd::string str("Test string");std::cout << "size: " << str.size() << "\n";std::cout << "length: " << str.length() << "\n";std::cout << "capacity: " << str.capacity() << "\n";std::cout << "max_size: " << str.max_size() << "\n";}{ // operator +=std::string name("John");std::string family("Smith");name += " K. ";         // c-stringname += family;         // stringname += '\n';           // characterstd::cout << name;}{ // operator =std::string str1, str2, str3;str1 = "Test string: ";   // c-stringstr2 = 'x';               // single characterstr3 = str1 + str2;       // stringstd::cout << str3 << '\n';}{ // operator []std::string str("Test string");for (int i = 0; i<str.length(); ++i) {std::cout << str[i];}}{ // pop_back(c++11)std::string str("hello world!");str.pop_back();std::cout << str << '\n';}{ // push_backstd::string str;std::ifstream file("test.txt", std::ios::in);if (file) {while (!file.eof()) str.push_back(file.get());}std::cout << str << '\n';}{ // rbegin/rendstd::string str("now step live...");for (std::string::reverse_iterator rit = str.rbegin(); rit != str.rend(); ++rit)std::cout << *rit;}{ // replacestd::string base = "this is a test string.";std::string str2 = "n example";std::string str3 = "sample phrase";std::string str4 = "useful.";// replace signatures used in the same order as described above:// Using positions:                 0123456789*123456789*12345std::string str = base;           // "this is a test string."str.replace(9, 5, str2);          // "this is an example string." (1)str.replace(19, 6, str3, 7, 6);     // "this is an example phrase." (2)str.replace(8, 10, "just a");     // "this is just a phrase."     (3)str.replace(8, 6, "a shorty", 7);  // "this is a short phrase."    (4)str.replace(22, 1, 3, '!');        // "this is a short phrase!!!"  (5)// Using iterators:                                               0123456789*123456789*str.replace(str.begin(), str.end() - 3, str3);                    // "sample phrase!!!"      (1)str.replace(str.begin(), str.begin() + 6, "replace");             // "replace phrase!!!"     (3)str.replace(str.begin() + 8, str.begin() + 14, "is coolness", 7);    // "replace is cool!!!"    (4)str.replace(str.begin() + 12, str.end() - 4, 4, 'o');                // "replace is cooool!!!"  (5)str.replace(str.begin() + 11, str.end(), str4.begin(), str4.end());// "replace is useful."    (6)std::cout << str << '\n';}{ // reservestd::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;}}{ // resizestd::string str("I like to code in C");std::cout << str << '\n';unsigned sz = str.size();str.resize(sz + 2, '+');std::cout << str << '\n';str.resize(14);std::cout << str << '\n';}{ // rfindstd::string str("The sixth sick sheik's sixth sheep's sick.");std::string key("sixth");std::size_t found = str.rfind(key);if (found != std::string::npos)str.replace(found, key.length(), "seventh");std::cout << str << '\n';}{ // shrink_to_fit(c++11)std::string str(100, 'x');std::cout << "1. capacity of str: " << str.capacity() << '\n';str.resize(10);std::cout << "2. capacity of str: " << str.capacity() << '\n';str.shrink_to_fit();std::cout << "3. capacity of str: " << str.capacity() << '\n';}{ // sizestd::string str("Test string");std::cout << "The size of str is " << str.size() << " bytes.\n";}{ // substrstd::string str = "We think in generalities, but we live in details.";// (quoting Alfred N. Whitehead)std::string str2 = str.substr(3, 5);     // "think"std::size_t pos = str.find("live");      // position of "live" in strstd::string str3 = str.substr(pos);     // get from "live" to the endstd::cout << str2 << ' ' << str3 << '\n';}{ // swapstd::string buyer("money");std::string seller("goods");std::cout << "Before the swap, buyer has " << buyer;std::cout << " and seller has " << seller << '\n';seller.swap(buyer);std::cout << " After the swap, buyer has " << buyer;std::cout << " and seller has " << seller << '\n';}{ // npos/*std::string::npos : public static member constantstatic const size_t npos = -1;npos is a static member constant value with the greatest possible value for an element of type size_t.This constant is defined with a value of -1, which because size_t is an unsigned integral type,it is the largest possible representable value for this type.*/}{ // getlinestd::string name;std::cout << "Please, enter your full name: ";std::getline(std::cin, name);std::cout << "Hello, " << name << "!\n";}{ // operator +std::string firstlevel("com");std::string secondlevel("cplusplus");std::string scheme("http://");std::string hostname;std::string url;hostname = "www." + secondlevel + '.' + firstlevel;url = scheme + hostname;std::cout << url << '\n';}{ // operator <<std::string str = "Hello world!";std::cout << str << '\n';}{ // operator >>std::string name;std::cout << "Please, enter your name: ";std::cin >> name;std::cout << "Hello, " << name << "!\n";}{ // string comparisonsstd::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";}{ // swap stringsstd::string buyer("money");std::string seller("goods");std::cout << "Before the swap, buyer has " << buyer;std::cout << " and seller has " << seller << '\n';swap(buyer, seller);std::cout << " After the swap, buyer has " << buyer;std::cout << " and seller has " << seller << '\n';}{ // stod(c++11)std::string orbits("365.24 29.53");std::string::size_type sz;     // alias of size_tdouble earth = std::stod(orbits, &sz);double moon = std::stod(orbits.substr(sz));std::cout << "The moon completes " << (earth / moon) << " orbits per Earth year.\n";}{ // stof(c++11)std::string orbits("686.97 365.24");std::string::size_type sz;     // alias of size_tfloat mars = std::stof(orbits, &sz);float earth = std::stof(orbits.substr(sz));std::cout << "One martian year takes " << (mars / earth) << " Earth years.\n";}{ // stoi(c++11)std::string str_dec = "2001, A Space Odyssey";std::string str_hex = "40c3";std::string str_bin = "-10010110001";std::string str_auto = "0x7f";std::string::size_type sz;   // alias of size_tint i_dec = std::stoi(str_dec, &sz);int i_hex = std::stoi(str_hex, nullptr, 16);int i_bin = std::stoi(str_bin, nullptr, 2);int i_auto = std::stoi(str_auto, nullptr, 0);std::cout << str_dec << ": " << i_dec << " and [" << str_dec.substr(sz) << "]\n";std::cout << str_hex << ": " << i_hex << '\n';std::cout << str_bin << ": " << i_bin << '\n';std::cout << str_auto << ": " << i_auto << '\n';}{ // stol(c++11)std::string str_dec = "1987520";std::string str_hex = "2f04e009";std::string str_bin = "-11101001100100111010";std::string str_auto = "0x7fffff";std::string::size_type sz;   // alias of size_tlong li_dec = std::stol(str_dec, &sz);long li_hex = std::stol(str_hex, nullptr, 16);long li_bin = std::stol(str_bin, nullptr, 2);long li_auto = std::stol(str_auto, nullptr, 0);std::cout << str_dec << ": " << li_dec << '\n';std::cout << str_hex << ": " << li_hex << '\n';std::cout << str_bin << ": " << li_bin << '\n';std::cout << str_auto << ": " << li_auto << '\n';}{ // stold(c++11)std::string orbits("90613.305 365.24");std::string::size_type sz;     // alias of size_tlong double pluto = std::stod(orbits, &sz);long double earth = std::stod(orbits.substr(sz));std::cout << "Pluto takes " << (pluto / earth) << " years to complete an orbit.\n";}{ // stoll(c++11)std::string str = "8246821 0xffff 020";std::string::size_type sz = 0;   // alias of size_twhile (!str.empty()) {long long ll = std::stoll(str, &sz, 0);std::cout << str.substr(0, sz) << " interpreted as " << ll << '\n';str = str.substr(sz);}}{ // stoul(c++11)std::string str{ "1111" };//std::cout << "Enter an unsigned number: ";//std::getline(std::cin, str);unsigned long ul = std::stoul(str, nullptr, 0);std::cout << "You entered: " << ul << '\n';}{ // stoull(c++11)std::string str = "8246821 0xffff 020 -1";std::string::size_type sz = 0;   // alias of size_twhile (!str.empty()) {unsigned long long ull = std::stoull(str, &sz, 0);std::cout << str.substr(0, sz) << " interpreted as " << ull << '\n';str = str.substr(sz);}}{ // to_string(c++11)/*string to_string (int val);string to_string (long val);string to_string (long long val);string to_string (unsigned val);string to_string (unsigned long val);string to_string (unsigned long long val);string to_string (float val);string to_string (double val);string to_string (long double val);*/std::string pi = "pi is " + std::to_string(3.1415926);std::string perfect = std::to_string(1 + 2 + 4 + 7 + 14) + " is a perfect number";std::cout << pi << '\n';std::cout << perfect << '\n';}{ // to_wstring(c++11)/*wstring to_wstring (int val);wstring to_wstring (long val);wstring to_wstring (long long val);wstring to_wstring (unsigned val);wstring to_wstring (unsigned long val);wstring to_wstring (unsigned long long val);wstring to_wstring (float val);wstring to_wstring (double val);wstring to_wstring (long double val);*/std::wstring pi = L"pi is " + std::to_wstring(3.1415926);std::wstring perfect = std::to_wstring(1 + 2 + 4 + 7 + 14) + L" is a perfect number";std::wcout << pi << L'\n';std::wcout << perfect << L'\n';}return 0;
}int test_string_ifstream_to_string()
{// reference: http://stackoverflow.com/questions/2602013/read-whole-ascii-file-into-c-stdstringstd::ifstream file("E:/GitCode/Messy_Test/testdata/regex.txt");if (!file) {fprintf(stderr, "read file failed!\n");return -1;}std::string str((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());fprintf(stderr, "file content: \n%s\n", str.c_str());return 0;
}

GitHub： https://github.com/fengbingchun/Messy_Test