C++/C++11中std string用法汇总
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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;
else
std::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 = hello
std::string s3 = s.substr(6); // s3 = world
std::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
", s2.c_str(), s3.c_str(), s4.c_str());
// insert、erase、assign
s.insert(s.size(), 5, ‘!‘); // 在s末尾插入5个感叹号
fprintf(stdout, "s: %s
", s.c_str());
s.erase(s.size() - 5, 5); // 从s删除最后5个字符
fprintf(stdout, "s: %s
", s.c_str());
const char* cp = "Stately, plump Buck";
s.assign(cp, 7); // s = "Stately"
fprintf(stdout, "s: %s
", s.c_str());
s.insert(s.size(), cp + 7); // s = "Stately, plump Buck"
fprintf(stdout, "s: %s
", 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
", 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
", 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
", 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
", 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
", 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
", 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
", 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
", 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
", 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c
toupper(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 << ‘
‘;
std::size_t found = str.find_last_of("/\");
std::cout << " path: " << str.substr(0, found) << ‘
‘;
std::cout << " file: " << str.substr(found + 1) << ‘
‘;
}
int test_string_func()
{
// reference: http://www.cplusplus.com/reference/string/string/
{ // append
std::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 << ‘
‘;
}
{ // assign
std::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 << ‘
‘;
str.assign(base, 10, 9);
std::cout << str << ‘
‘; // "brown fox"
str.assign("pangrams are cool", 7);
std::cout << str << ‘
‘; // "pangram"
str.assign("c-string");
std::cout << str << ‘
‘; // "c-string"
str.assign(10, ‘*‘);
std::cout << str << ‘
‘; // "**********"
str.assign(10, 0x2D);
std::cout << str << ‘
‘; // "----------"
str.assign(base.begin() + 16, base.end() - 12);
std::cout << str << ‘
‘; // "fox jumps over"
}
{ // at
std::string str("Test string");
for (unsigned i = 0; i<str.length(); ++i) {
std::cout << str.at(i);
}
std::cout << ‘
‘;
}
{ // back(c++11)
std::string str("hello world.");
str.back() = ‘!‘;
std::cout << str << ‘
‘;
}
{ // begin/end
std::string str("Test string");
for (std::string::iterator it = str.begin(); it != str.end(); ++it)
std::cout << *it;
std::cout << ‘
‘;
}
{ // capacity
std::string str("Test string");
std::cout << "size: " << str.size() << "
";
std::cout << "length: " << str.length() << "
";
std::cout << "capacity: " << str.capacity() << "
";
std::cout << "max_size: " << str.max_size() << "
";
}
{ // cbegin/cend(c++11)
std::string str("Lorem ipsum");
for (auto it = str.cbegin(); it != str.cend(); ++it)
std::cout << *it;
std::cout << ‘
‘;
}
{ // clear
char c;
std::string str;
std::cout << "Please type some lines of text. Enter a dot (.) to finish:
";
do {
c = std::cin.get();
str += c;
if (c == ‘
‘) {
std::cout << str;
str.clear();
}
} while (c != ‘.‘);
}
{ // compare
std::string str1("green apple");
std::string str2("red apple");
if (str1.compare(str2) != 0)
std::cout << str1 << " is not " << str2 << ‘
‘;
if (str1.compare(6, 5, "apple") == 0)
std::cout << "still, " << str1 << " is an apple
";
if (str2.compare(str2.size() - 5, 5, "apple") == 0)
std::cout << "and " << str2 << " is also an apple
";
if (str1.compare(6, 5, str2, 4, 5) == 0)
std::cout << "therefore, both are apples
";
}
{ // copy
char buffer[20];
std::string str("Test string...");
std::size_t length = str.copy(buffer, 6, 5);
buffer[length] = ‘ ‘;
std::cout << "buffer contains: " << buffer << ‘
‘;
}
{ // crbegin/crend(c++11)
std::string str("lorem ipsum");
for (auto rit = str.crbegin(); rit != str.crend(); ++rit)
std::cout << *rit;
std::cout << ‘
‘;
}
{ // c_str
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 str
char * p = std::strtok(cstr, " ");
while (p != 0) {
std::cout << p << ‘
‘;
p = std::strtok(NULL, " ");
}
delete[] cstr;
}
{ // data
int 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.
";
if (memcmp(cstr, str.data(), str.length()) == 0)
std::cout << "str and cstr have the same content.
";
}
}
{ // empty
std::string content;
std::string line;
std::cout << "Please introduce a text. Enter an empty line to finish:
";
do {
getline(std::cin, line);
content += line + ‘
‘;
} while (!line.empty());
std::cout << "The text you introduced was:
" << content;
}
{ // erase
std::string str("This is an example sentence.");
std::cout << str << ‘
‘;
// "This is an example sentence."
str.erase(10, 8); // ^^^^^^^^
std::cout << str << ‘
‘;
// "This is an sentence."
str.erase(str.begin() + 9); // ^
std::cout << str << ‘
‘;
// "This is a sentence."
str.erase(str.begin() + 5, str.end() - 9); // ^^^^^
std::cout << str << ‘
‘;
// "This sentence."
}
{ // find
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::size_t found = str.find(str2);
if (found != std::string::npos)
std::cout << "first ‘needle‘ found at: " << found << ‘
‘;
found = str.find("needles are small", found + 1, 6);
if (found != std::string::npos)
std::cout << "second ‘needle‘ found at: " << found << ‘
‘;
found = str.find("haystack");
if (found != std::string::npos)
std::cout << "‘haystack‘ also found at: " << found << ‘
‘;
found = str.find(‘.‘);
if (found != std::string::npos)
std::cout << "Period found at: " << found << ‘
‘;
// let‘s replace the first needle:
str.replace(str.find(str2), str2.length(), "preposition");
std::cout << str << ‘
‘;
}
{ // find_first_not_of
std::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 << ‘
‘;
}
}
{ // find_first_of
std::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 << ‘
‘;
}
{ // find_last_not_of
std::string str("Please, erase trailing white-spaces
");
std::string whitespaces(" fv
");
std::size_t found = str.find_last_not_of(whitespaces);
if (found != std::string::npos)
str.erase(found + 1);
else
str.clear(); // str is all whitespace
std::cout << ‘[‘ << str << "]
";
}
{ // find_last_of
std::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 << ‘
‘;
}
{ // get_allocator
// reference: http://www.tenouk.com/cpluscodesnippet/cplusbasic_stringget_allocator.html
// using the default allocator
std::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 str1
std::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;
else
std::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 str1
std::string str5(xchar);
}
{ // insert
std::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 )question
str.insert(6, str3, 3, 4); // to be (not )the question
str.insert(10, "that is cool", 8); // to be not (that is )the question
str.insert(10, "to be "); // to be not (to be )that is the question
str.insert(15, 1, ‘:‘); // to be not to be(:) that is the question
it = str.insert(str.begin() + 5, ‘,‘); // to be(,) not to be: that is the question
str.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 << ‘
‘;
}
{ // length
std::string str("Test string");
std::cout << "The size of str is " << str.length() << " bytes.
";
}
{ // max_size
std::string str("Test string");
std::cout << "size: " << str.size() << "
";
std::cout << "length: " << str.length() << "
";
std::cout << "capacity: " << str.capacity() << "
";
std::cout << "max_size: " << str.max_size() << "
";
}
{ // operator +=
std::string name("John");
std::string family("Smith");
name += " K. "; // c-string
name += family; // string
name += ‘
‘; // character
std::cout << name;
}
{ // operator =
std::string str1, str2, str3;
str1 = "Test string: "; // c-string
str2 = ‘x‘; // single character
str3 = str1 + str2; // string
std::cout << str3 << ‘
‘;
}
{ // 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 << ‘
‘;
}
{ // push_back
std::string str;
std::ifstream file("test.txt", std::ios::in);
if (file) {
while (!file.eof()) str.push_back(file.get());
}
std::cout << str << ‘
‘;
}
{ // rbegin/rend
std::string str("now step live...");
for (std::string::reverse_iterator rit = str.rbegin(); rit != str.rend(); ++rit)
std::cout << *rit;
}
{ // replace
std::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*12345
std::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 << ‘
‘;
}
{ // reserve
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;
}
}
{ // resize
std::string str("I like to code in C");
std::cout << str << ‘
‘;
unsigned sz = str.size();
str.resize(sz + 2, ‘+‘);
std::cout << str << ‘
‘;
str.resize(14);
std::cout << str << ‘
‘;
}
{ // rfind
std::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 << ‘
‘;
}
{ // shrink_to_fit(c++11)
std::string str(100, ‘x‘);
std::cout << "1. capacity of str: " << str.capacity() << ‘
‘;
str.resize(10);
std::cout << "2. capacity of str: " << str.capacity() << ‘
‘;
str.shrink_to_fit();
std::cout << "3. capacity of str: " << str.capacity() << ‘
‘;
}
{ // size
std::string str("Test string");
std::cout << "The size of str is " << str.size() << " bytes.
";
}
{ // substr
std::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 str
std::string str3 = str.substr(pos); // get from "live" to the end
std::cout << str2 << ‘ ‘ << str3 << ‘
‘;
}
{ // swap
std::string buyer("money");
std::string seller("goods");
std::cout << "Before the swap, buyer has " << buyer;
std::cout << " and seller has " << seller << ‘
‘;
seller.swap(buyer);
std::cout << " After the swap, buyer has " << buyer;
std::cout << " and seller has " << seller << ‘
‘;
}
{ // npos
/*
std::string::npos : public static member constant
static 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.
*/
}
{ // getline
std::string name;
std::cout << "Please, enter your full name: ";
std::getline(std::cin, name);
std::cout << "Hello, " << name << "!
";
}
{ // 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 << ‘
‘;
}
{ // operator <<
std::string str = "Hello world!";
std::cout << str << ‘
‘;
}
{ // operator >>
std::string name;
std::cout << "Please, enter your name: ";
std::cin >> name;
std::cout << "Hello, " << name << "!
";
}
{ // string comparisons
std::string foo = "alpha";
std::string bar = "beta";
if (foo == bar) std::cout << "foo and bar are equal
";
if (foo != bar) std::cout << "foo and bar are not equal
";
if (foo< bar) std::cout << "foo is less than bar
";
if (foo> bar) std::cout << "foo is greater than bar
";
if (foo <= bar) std::cout << "foo is less than or equal to bar
";
if (foo >= bar) std::cout << "foo is greater than or equal to bar
";
}
{ // swap strings
std::string buyer("money");
std::string seller("goods");
std::cout << "Before the swap, buyer has " << buyer;
std::cout << " and seller has " << seller << ‘
‘;
swap(buyer, seller);
std::cout << " After the swap, buyer has " << buyer;
std::cout << " and seller has " << seller << ‘
‘;
}
{ // stod(c++11)
std::string orbits("365.24 29.53");
std::string::size_type sz; // alias of size_t
double earth = std::stod(orbits, &sz);
double moon = std::stod(orbits.substr(sz));
std::cout << "The moon completes " << (earth / moon) << " orbits per Earth year.
";
}
{ // stof(c++11)
std::string orbits("686.97 365.24");
std::string::size_type sz; // alias of size_t
float mars = std::stof(orbits, &sz);
float earth = std::stof(orbits.substr(sz));
std::cout << "One martian year takes " << (mars / earth) << " Earth years.
";
}
{ // 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_t
int 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) << "]
";
std::cout << str_hex << ": " << i_hex << ‘
‘;
std::cout << str_bin << ": " << i_bin << ‘
‘;
std::cout << str_auto << ": " << i_auto << ‘
‘;
}
{ // 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_t
long 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 << ‘
‘;
std::cout << str_hex << ": " << li_hex << ‘
‘;
std::cout << str_bin << ": " << li_bin << ‘
‘;
std::cout << str_auto << ": " << li_auto << ‘
‘;
}
{ // stold(c++11)
std::string orbits("90613.305 365.24");
std::string::size_type sz; // alias of size_t
long 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.
";
}
{ // stoll(c++11)
std::string str = "8246821 0xffff 020";
std::string::size_type sz = 0; // alias of size_t
while (!str.empty()) {
long long ll = std::stoll(str, &sz, 0);
std::cout << str.substr(0, sz) << " interpreted as " << ll << ‘
‘;
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 << ‘
‘;
}
{ // stoull(c++11)
std::string str = "8246821 0xffff 020 -1";
std::string::size_type sz = 0; // alias of size_t
while (!str.empty()) {
unsigned long long ull = std::stoull(str, &sz, 0);
std::cout << str.substr(0, sz) << " interpreted as " << ull << ‘
‘;
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 << ‘
‘;
std::cout << perfect << ‘
‘;
}
{ // 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‘
‘;
std::wcout << perfect << L‘
‘;
}
return 0;
}
int test_string_ifstream_to_string()
{
// reference: http://stackoverflow.com/questions/2602013/read-whole-ascii-file-into-c-stdstring
std::ifstream file("E:/GitCode/Messy_Test/testdata/regex.txt");
if (!file) {
fprintf(stderr, "read file failed!
");
return -1;
}
std::string str((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());
fprintf(stderr, "file content:
%s
", str.c_str());
return 0;
}
GitHub:https://github.com/fengbingchun/Messy_Test
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