C++ sstream

sstream

• <sstream> 라이브러리

• stringstream의 약자이다.

• << : insertion operator

• >> : extraction operator

상속 관계

• istringstream, ostringstream, stringstream은 비슷하지만 약간 다른 부분이 존재한다.

  • istringstream에 << 연산자는 정의되어있지 않다.

  • ostringstream에 >> 연산자는 정의되어있지 않다.

  <iosfwd>

  using istringstream = basic_istringstream<char, char_traits<char>, allocator<char>>;
  using ostringstream = basic_ostringstream<char, char_traits<char>, allocator<char>>;
  using stringstream  = basic_stringstream<char, char_traits<char>, allocator<char>>;

  <sstream>

  // CLASS TEMPLATE basic_istringstream
  template <class _Elem, class _Traits, class _Alloc>
  class basic_istringstream : public basic_istream<_Elem, _Traits> { // input stream associated with a character array
  };
  
  // CLASS TEMPLATE basic_ostringstream
  template <class _Elem, class _Traits, class _Alloc>
  class basic_ostringstream : public basic_ostream<_Elem, _Traits> { // output stream associated with a character array
  }
  
  // CLASS TEMPLATE basic_stringstream
  template <class _Elem, class _Traits, class _Alloc>
  class basic_stringstream
      : public basic_iostream<_Elem, _Traits> { // input/output stream associated with a character array
  }

기본 예제

• stringstream 사용

  #include <iostream>
  #include <sstream>
  
  int         main()
  {
      using namespace std;
  
      stringstream ss;
      ss << "Hello, World";
      ss << '!';
  
      string str;
      ss >> str;
      cout << str << endl;
  
      ss.str("Hello World!");
      str = ss.str();
      cout << str << endl;
  
      ss.str("");
      cout << boolalpha << ss.str().empty() << endl;
  }
  
  /* stdout stderr
  Hello,
  Hello World!
  true
  */

• 숫자 넣기

  #include <iostream>
  #include <sstream>
  
  int         main()
  {
      using namespace std;
  
      stringstream ss;
  
      ss << "12345 67.89";
  
      int     i;
      double  d;
  
      ss >> i >> d;
  
      cout << i << '|' << d << endl;
  }
  
  

/* stdout stderr
12345|67.89
*/

- `istringstream`, `ostringstream` 사용

  ```c++
  #include <iostream>
  #include <string>
  #include <sstream>

  template <typename T>
  std::string ToString(T x)
  {
    std::ostringstream osstream;
    osstream << x;
    return osstream.str();
  }

  template <typename T>
  bool        FromString(const std::string& str, T& x)
  {
    std::istringstream isstream(str);
    return (isstream >> x ? true : false);
  }

  int         main()
  {
    using namespace std;

    string my_str(ToString(3.141592));
    cout << my_str << endl;

    double d;
    if (FromString(my_str, d))
      cout << d << endl;
    else
      cout << "Cannot conver string to double\n";
    if (FromString("Hello", d))
      cout << d << endl;
    else
      cout << "Cannot conver string to double\n";
  }

  /* stdout stderr
  3.14159
  3.14159
  Cannot conver string to double
  */