[C++学习笔记09]string

1. string的定义原型
   

   typedef basic_string<char, char_traits<char>, allocator<char> >
       string; 
   typedef basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t> >
       wstring;
   
   // 第二三个参数有默认值

   ---

2. string部分构造方式
   

   // string 部分构造方式
   #include <iostream>
   #include <string>
   using namespace std;
   
   int main(void)
   {
       string s1;
       string s2("ABCDEFG");
       cout << s1 << endl;
       cout << s2 << endl;
   
       // 使用最初的形式定义
       basic_string<char> s3("xxxx");
       cout << s3 << endl;
   
       /*
           basic_string(
               const value_type *_Ptr, 
               size_type _Count
           );
       */
       string s4("DEFG", 2);
       cout << s4 << endl; // DE
       /*
           basic_string(
               const basic_string& _Right, 
               size_type _Roff,
               size_type _Count = npos
           );
       */
       string s5(s2, 2, 2);
       cout << s5 << endl; //CD
   
       /*
       basic_string(
          const_iterator _First,
          const_iterator _Last
       );
       */
       string::const_iterator first = s2.begin() + 1;
       string::const_iterator end = s2.begin() + 3; // [first, end)
       string s6(first, end);
       cout << s6 << endl; // BC
   
       return 0;
   
   }

   ---

    

3. string常用成员函数
   

   // string 部分成员函数部分形式操作
   #include <iostream>
   #include <string>
   using namespace std;
   
   
   int main(void)
   {
       string s1("ABCDEC");
       cout << s1.size() << endl;
       cout << s1.length() << endl;
   
       cout << s1.empty() << endl;
       // 一样第二个参数是count,不是截至位置
       string s2 = s1.substr(1, /*4*/string::npos); // string::npos == 4294967295
       cout << s2 << endl;
   
       //find
       /*
           size_type find(
               value_type _Ch, 
               size_type _Off = 0
           ) const;
       */
       // 查找某个字符在string中第一次出现的位置（下标）,没找到返回 4294967295 最大值
       cout << s1.find('C') << endl; // 2
       //size_type -> size_t ->unsigned int
       /*
           size_type find(
               const value_type* _Ptr,
               size_type _Off = 0
           ) const;
       */
       // 在string中查找字符串，找到返回第一次出现位置的下标，没找到返回 string::npos， 4294967295 最大值
       cout << s1.find("CD") << endl; // 2
       /*
       size_type find(
           const basic_string<CharType, Traits, Allocator>& _Str,
           size_type _Off = 0
           ) const;
       */
       // 在string中查找string
       cout << s1.find(s2) << endl;
   
       //rfind,反向查找，返回第一次查找到的下标
       cout << s1.rfind('C') << endl; // 5
   
       //replace
       /*
           basic_string<CharType, Traits, Allocator>& replace(
              size_type _Pos1, 
              size_type _Num1,
              const value_type* _Ptr
           );
       */
       // 第三个参数也能是string，这里不写了，只介绍这一个好了
       string s3 = s1;
       s3.replace(1, 2, "RRR");
       cout << s3 << endl; // ARRRDEC
   
       // compare 
       cout << s3.compare(s1) << endl; // 1, s3 > s1
   
       // insert
       /*
           basic_string<CharType, Traits, Allocator>& insert(
              size_type _P0, 
              const value_type* _Ptr
           );
       */
       s3.insert(2, "aaaaaaaaaaa");
       cout << s3 << endl; // ARaaaaaaaaaaaRRDEC
   
       // append
       /*
           basic_string<CharType, Traits, Allocator>& append(
               const value_type* _Ptr
           );
       */
       s3.append("OOOOOOOOOOOOOOOOO");
       cout << s3 << endl; // ARaaaaaaaaaaaRRDECOOOOOOOOOOOOOOOOO
   
       // swap
       /*
           void swap(
               basic_string<CharType, Traits, Allocator>& _Str
           );
       */
       s3.swap(s2);
       cout << s3 << endl;
       cout << s2 << endl;
   
       return 0;
   }

   ---

4. string综合应用
   　　在字符集中查找存在的首尾字符，并截取。
   

   #include <iostream>
   #include <string>
   using namespace std;
   
   int main()
   {
       string strinfo = " //*---------Hello World!--------------*//";
       string strset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
       /*
           size_type find_first_of(
               const basic_string<CharType, Traits, Allocator>& _Str,
               size_type _Off = 0
           ) const;
       */
       string::size_type first = strinfo.find_first_of(strset);
       if (first == string::npos)
           cout << "not found." << endl;
       string::size_type end = strinfo.find_last_of(strset);
       if (end == string::npos)
           cout << "not found." << endl;
       //cout << "string::npos" << string::npos << endl; // string::npos == 4294967295
       cout << strinfo.substr(first, end - first + 1) << endl;
   
       return 0;
   }

   ---

    

5. string简单去除字符串左右空格
   

   // string 简单实现去除字符串左右空格
   #include <iostream>
   #include <string>
   using namespace std;
   
   class StringUtils {
   public:
       static void LTrim(string &s)
       {
           string drop = " \t";
           s.erase(0, s.find_first_not_of(drop));
       }
   
       static void RTrim(string &s)
       {
           string drop = " \t";
           s.erase(s.find_last_not_of(drop)+1);
       }
   
       static void Trim(string &s)
       {
           LTrim(s);
           RTrim(s);
       }
   };
   
   int main(void)
   {
       string s1 = "               ABCD                ";
       StringUtils::Trim(s1);
       cout << s1 << endl; // "ABCD"
       cout << s1.size() << endl; // 4
   
       return 0;
   }

   ---