从零开始学C++之标准库类型（一）：string 类简介和例程

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一、标准库string类型

string类型支持长度可变的字符串，C++标准库将负责管理与存储字符相关的内存，以及提供各种有用的操作 ，在VC中直接F1查看

template <
class CharType,
class Traits=char_traits<CharType>,
class Allocator=allocator<CharType>
>
class basic_string

typedef basic_string<char> string;

typedef basic_string<wchar_t> wstring;

要使用string类型对象，必须包含相关头文件

#include <string>

using std::string;

string对象的定义和初始化：

string s1; //默认构造函数，s1为空串

string s2(s1); //将s2初始化为s1的一个副本

string s3(“value”);
//将s3初始化为一个字符串字面值副本

string s4(n, ‘c’);
//将s4初始化为字符‘c’的n个副本

常用成员函数：



例程1：

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#include <string> #include <iostream> using namespace std; int main(void) { string s1; string s2("abcdefghijkl"); cout << s2 << endl; basic_string<char> s3("xxx"); // 等价于string s3("xxx"); cout << s3 << endl; string s4("abcdefg", 4); cout << s4 << endl; string s5(s2, 2, 3); cout << s5 << endl; string::iterator first = s2.begin() + 1; string::iterator last = s2.begin() + 3; string s6(first, last); //[first, last) cout << s6 << endl; return 0; }

例程2：

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#include <string> #include <iostream> using namespace std; int main(void) { string s1("abcdefdg"); cout << s1.size() << endl; cout << s1.length() << endl; cout << s1.empty() << endl; cout << s1.substr(1, 2) << endl; cout << s1.substr(1) << endl; //等价于s1.substr(1, -1); string::size_type pos = s1.find('d', 1);//位置从0开始算起 if (pos == string::npos) //npos = -1 cout << "not found" << endl; else cout << "pos=" << pos << endl; pos = s1.rfind('d'); if (pos == string::npos) cout << "not found" << endl; else cout << "pos=" << pos << endl; return 0; }

例程3：

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#include <string> #include <iostream> using namespace std; int main(void) { string s1("abcdefghijkl"); s1.replace(2, 2, "AAAAAA"); cout << s1 << endl; s1 = "abcdefg"; s1.replace(s1.begin() + 1, s1.begin() + 4, "AAAAAA"); cout << s1 << endl; string s2 = "xyzabc"; s2.insert(2, "MMMM"); //在位置2之前插入 cout << s2 << endl; s2.append("6666"); cout << s2 << endl; string s3 = "111"; s2.swap(s3); cout << s2 << endl; cout << s3 << endl; return 0; }

例程4：

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#include <string> #include <iostream> using namespace std; void fun(char *str) { cout << str << endl; } int main(void) { string s1 = "abc"; s1[1] = 'B'; cout << s1 << endl; const string s2 = "xyz"; //s2[1] = 'Y'; Error s2[1] 返回的是 const char& string s3 = "111" + s1 + "222" ; cout << s3 << endl; //s3.c_str() fun(const_cast<char *>(s3.c_str())); return 0; }

例程5：

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#include <string> #include <iostream> using namespace std; int main() { string strinfo = " //*---Hello World!......------"; string strset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"; string::size_type first = strinfo.find_first_of(strset); if(first == string::npos) cout << "not find any characters" << endl; string::size_type last = strinfo.find_last_of(strset); if(last == string::npos) cout << "not find any characters" << endl; cout << strinfo.substr(first, last - first + 1) << endl; return 0; }

输出：Hello World

可以利用find_first_of 等操作去除空格，如去除左空格可以这样：

string s = " afas";

string drop = " \t";

s.erase(0, s.find_first_not_of(drop));

去除右空格：

string s = " dsfs ";

string drop = " \t";

s.erase(s.find_last_not_of(drop)+1);

参考：

C++ primer 第四版

Effective C++ 3rd

C++编程规范