cppreference.com > C++ Strings > String constructors String constructors Syntax:
      #include <string>
      string();
      string( const string& s );
      string( size_type length, const char& ch );
      string( const char* str );
      string( const char* str, size_type length );
      string( const string& str, size_type index, size_type length );
      string( input_iterator start, input_iterator end );
      ~string();
The string constructors create a new string containing: nothing; an empty string, a copy of the given string s, length copies of ch, a duplicate of str (optionally up to length characters long), a substring of str starting at index and length characters long a string of characterss denoted by the start and end iterators For example,
       string str1( 5, 'c' );
       string str2( "Now is the time..." );
       string str3( str2, 11, 4 );
       cout << str1 << endl;
       cout << str2 << endl;
       cout << str3 << endl;
displays
       ccccc
       Now is the time...
       time
The string constructors usually run in linear time, except the empty constructor, which runs in constant time.