C++基础---string类的data/c_str/copy

1.string类的data/c_str/copy

1.1 std::string::data

• 原型： const char *data()const;
• 功能： string型字符串转化为char型字符串。
• 说明：将自身转化为一个以空终止符结束（即带”\0“结尾）的char型字符串。
• 返回值：一个指向字符串数组的指针，字符串数组指针。

• 代码示例：

  (1)示例代码一：
  
  #include <iostream>
  
  
  #include <string>
  
  using namespace std;
  int main ()
  {
      string str = "Test string";
      char *cstr = "Test string";
  
      if (str.length() == strlen(cstr))
      {
          cout<<"str and cstr have the same length."<<endl;
  
          if (memcmp(cstr, str.data(), str.length()) == 0)
          {
              cout<<"str and cstr have the same content."<<endl;
          }
      }
  
      system("pause");
      return 0;
  }
  =>str and cstr have the same length.
    str and cstr have the same content.

  (2)示例代码二：
  
  #include <iostream>
  
  
  #include <string>
  
  using namespace std;
  int main ()
  {
      string str("Please split this sentence into tokens");
      const char *split = " ";
      char *cstr = new char [str.length()+1];
      strcpy_s(cstr, str.size() + 1, str.data());
  
      //cstr now contains a c-string copy of str
      char *p = 0;
      char *pNext = 0;
      p = strtok_s(cstr, split, &pNext);
      while(p != 0)
      {
          cout<<p<<endl;
          p = strtok_s(NULL, split, &pNext);
      }
  
      delete[] cstr;
      system("pause");
  
      return 0;
  }   
  =>Please
    split
    this
    sentence
    into
    tokens

1.2 std::string::c_str

• 原型：const char *c_str()const;
• 功能： string型字符串转化为char型字符串。
• 说明：将自身转化为一个以空终止符结束（即带”\0“结尾）的char型字符串。
• 返回值：一个指向字符串数组的指针，字符串数组指针。

• 代码示例：

  (1)示例代码一：
  
  #include <iostream>
  
  
  #include <string>
  
  using namespace std;
  int main ()
  {
      string str = "Test string";
      char *cstr = "Test string";
  
      if (str.length() == strlen(cstr))
      {
          cout<<"str and cstr have the same length."<<endl;
  
          if (memcmp(cstr, str.c_str(), str.length()) == 0)
          {
              cout<<"str and cstr have the same content"<<endl;
          }
      }
  
      system("pause");
      return 0;
  }
  =>str and cstr have the same length.
    str and cstr have the same content.

  (2)示例代码二：
  
  #include <iostream>
  
  
  #include <string>
  
  using namespace std;
  int main ()
  {
      string str("Please split this sentence into tokens");
      const char *split = " ";
      char *cstr = new char [str.length()+1];
      strcpy_s(cstr, str.size() + 1, str.c_str());
  
      //cstr now contains a c-string copy of str
      char *p = 0;
      char *pNext = 0;
      p = strtok_s(cstr, split, &pNext);
      while (p != 0)
      {
          cout<<p<<endl;
          p = strtok_s(NULL, split, &pNext);
      }
  
      delete[] cstr;
      system("pause");
  
      return 0;
  }
  =>Please
    split
    this
    sentence
    into
    tokens

1.3 std::string::copy

• 原型：size_t copy (char* s, size_t len, size_t pos = 0) const;
• 功能： string型字符串转化为char型字符串。
• 说明：从源字符串以下标为pos（默认为0）处开始拷贝n个字符到char型字符串s中。
• 返回值：实际拷贝的字符个数。

• 代码示例：

  
  #pragma warning(disable:4996) //全部关掉
  
  
  #include <iostream>
  
  
  #include <string>
  
  using namespace std;
  int main ()
  {
      char buffer[20];
      string str("Test string...");
      size_t length = str.copy(buffer, 6, 5);
      buffer[length]='\0';
      cout<<"buffer contains: "<<buffer<<endl;
      system("pause");
      return 0;
  }
  =>buffer contains: string

参考文献：
[1] 网络资源： http://www.cplusplus.com/reference/string/string/data/
       http://www.cplusplus.com/reference/string/string/c_str/
       http://www.cplusplus.com/reference/string/string/copy/