*  @return  Read-only (const) reference to the character.       *  @throw  std::out_of_range  If @a n is an invalid index.       *       *  This function provides for safer data access.  The parameter is       *  first checked that it is in the range of the string.  The function       *  throws out_of_range if the check fails.       */      const_reference      at(size_type __n) const      {	if (__n >= this->size())	  __throw_out_of_range(__N("basic_string::at"));	return _M_data()[__n];      }      /**       *  @brief  Provides access to the data contained in the %string.       *  @param n The index of the character to access.       *  @return  Read/write reference to the character.       *  @throw  std::out_of_range  If @a n is an invalid index.       *       *  This function provides for safer data access.  The parameter is       *  first checked that it is in the range of the string.  The function       *  throws out_of_range if the check fails.  Success results in       *  unsharing the string.       */      reference      at(size_type __n)      {	if (__n >= size())	  __throw_out_of_range(__N("basic_string::at"));	_M_leak();	return _M_data()[__n];      }      // Modifiers:      /**       *  @brief  Append a string to this string.       *  @param str  The string to append.       *  @return  Reference to this string.       */      basic_string&      operator+=(const basic_string& __str)      { return this->append(__str); }      /**       *  @brief  Append a C string.       *  @param s  The C string to append.       *  @return  Reference to this string.       */      basic_string&      operator+=(const _CharT* __s)      { return this->append(__s); }      /**       *  @brief  Append a character.       *  @param c  The character to append.       *  @return  Reference to this string.       */      basic_string&      operator+=(_CharT __c)      { 	this->push_back(__c);	return *this;      }      /**       *  @brief  Append a string to this string.       *  @param str  The string to append.       *  @return  Reference to this string.       */      basic_string&      append(const basic_string& __str);      /**       *  @brief  Append a substring.       *  @param str  The string to append.       *  @param pos  Index of the first character of str to append.       *  @param n  The number of characters to append.       *  @return  Reference to this string.       *  @throw  std::out_of_range if @a pos is not a valid index.       *       *  This function appends @a n characters from @a str starting at @a pos       *  to this string.  If @a n is is larger than the number of available       *  characters in @a str, the remainder of @a str is appended.       */      basic_string&      append(const basic_string& __str, size_type __pos, size_type __n);      /**       *  @brief  Append a C substring.       *  @param s  The C string to append.       *  @param n  The number of characters to append.       *  @return  Reference to this string.       */      basic_string&      append(const _CharT* __s, size_type __n);      /**       *  @brief  Append a C string.       *  @param s  The C string to append.       *  @return  Reference to this string.       */      basic_string&      append(const _CharT* __s)      {	__glibcxx_requires_string(__s);	return this->append(__s, traits_type::length(__s));      }      /**       *  @brief  Append multiple characters.       *  @param n  The number of characters to append.       *  @param c  The character to use.       *  @return  Reference to this string.       *       *  Appends n copies of c to this string.       */      basic_string&      append(size_type __n, _CharT __c);      /**       *  @brief  Append a range of characters.       *  @param first  Iterator referencing the first character to append.       *  @param last  Iterator marking the end of the range.       *  @return  Reference to this string.       *       *  Appends characters in the range [first,last) to this string.       */      template<class _InputIterator>        basic_string&        append(_InputIterator __first, _InputIterator __last)        { return this->replace(_M_iend(), _M_iend(), __first, __last); }      /**       *  @brief  Append a single character.       *  @param c  Character to append.       */      void      push_back(_CharT __c)      { 	const size_type __len = 1 + this->size();	if (__len > this->capacity() || _M_rep()->_M_is_shared())	  this->reserve(__len);	traits_type::assign(_M_data()[this->size()], __c);	_M_rep()->_M_set_length_and_sharable(__len);      }      /**       *  @brief  Set value to contents of another string.       *  @param  str  Source string to use.       *  @return  Reference to this string.       */      basic_string&      assign(const basic_string& __str);      /**       *  @brief  Set value to a substring of a string.       *  @param str  The string to use.       *  @param pos  Index of the first character of str.       *  @param n  Number of characters to use.       *  @return  Reference to this string.       *  @throw  std::out_of_range if @a pos is not a valid index.       *       *  This function sets this string to the substring of @a str consisting       *  of @a n characters at @a pos.  If @a n is is larger than the number       *  of available characters in @a str, the remainder of @a str is used.       */      basic_string&      assign(const basic_string& __str, size_type __pos, size_type __n)      { return this->assign(__str._M_data()			    + __str._M_check(__pos, "basic_string::assign"),			    __str._M_limit(__pos, __n)); }      /**       *  @brief  Set value to a C substring.       *  @param s  The C string to use.       *  @param n  Number of characters to use.       *  @return  Reference to this string.       *       *  This function sets the value of this string to the first @a n       *  characters of @a s.  If @a n is is larger than the number of       *  available characters in @a s, the remainder of @a s is used.       */      basic_string&      assign(const _CharT* __s, size_type __n);      /**       *  @brief  Set value to contents of a C string.       *  @param s  The C string to use.       *  @return  Reference to this string.       *       *  This function sets the value of this string to the value of @a s.       *  The data is copied, so there is no dependence on @a s once the       *  function returns.       */      basic_string&      assign(const _CharT* __s)      {	__glibcxx_requires_string(__s);	return this->assign(__s, traits_type::length(__s));      }      /**       *  @brief  Set value to multiple characters.       *  @param n  Length of the resulting string.       *  @param c  The character to use.       *  @return  Reference to this string.       *       *  This function sets the value of this string to @a n copies of       *  character @a c.       */      basic_string&      assign(size_type __n, _CharT __c)      { return _M_replace_aux(size_type(0), this->size(), __n, __c); }      /**       *  @brief  Set value to a range of characters.       *  @param first  Iterator referencing the first character to append.       *  @param last  Iterator marking the end of the range.       *  @return  Reference to this string.       *       *  Sets value of string to characters in the range [first,last).      */      template<class _InputIterator>        basic_string&        assign(_InputIterator __first, _InputIterator __last)        { return this->replace(_M_ibegin(), _M_iend(), __first, __last); }      /**       *  @brief  Insert multiple characters.       *  @param p  Iterator referencing location in string to insert at.       *  @param n  Number of characters to insert       *  @param c  The character to insert.       *  @throw  std::length_error  If new length exceeds @c max_size().       *       *  Inserts @a n copies of character @a c starting at the position       *  referenced by iterator @a p.  If adding characters causes the length       *  to exceed max_size(), length_error is thrown.  The value of the       *  string doesn't change if an error is thrown.      */      void      insert(iterator __p, size_type __n, _CharT __c)      {	this->replace(__p, __p, __n, __c);  }      /**       *  @brief  Insert a range of characters.       *  @param p  Iterator referencing location in string to insert at.       *  @param beg  Start of range.       *  @param end  End of range.       *  @throw  std::length_error  If new length exceeds @c max_size().       *       *  Inserts characters in range [beg,end).  If adding characters causes       *  the length to exceed max_size(), length_error is thrown.  The value       *  of the string doesn't change if an error is thrown.      */      template<class _InputIterator>        void        insert(iterator __p, _InputIterator __beg, _InputIterator __end)        { this->replace(__p, __p, __beg, __end); }      /**       *  @brief  Insert value of a string.       *  @param pos1  Iterator referencing location in string to insert at.       *  @param str  The string to insert.       *  @return  Reference to this string.       *  @throw  std::length_error  If new length exceeds @c max_size().       *       *  Inserts value of @a str starting at @a pos1.  If adding characters       *  causes the length to exceed max_size(), length_error is thrown.  The       *  value of the string doesn't change if an error is thrown.      */      basic_string&      insert(size_type __pos1, const basic_string& __str)      { return this->insert(__pos1, __str, size_type(0), __str.size()); }      /**       *  @brief  Insert a substring.       *  @param pos1  Iterator referencing location in string to insert at.       *  @param str  The string to insert.       *  @param pos2  Start of characters in str to insert.       *  @param n  Number of characters to insert.       *  @return  Reference to this string.       *  @throw  std::length_error  If new length exceeds @c max_size().       *  @throw  std::out_of_range  If @a pos1 > size() or       *  @a pos2 > @a str.size().       *       *  Starting at @a pos1, insert @a n character of @a str beginning with       *  @a pos2.  If adding characters causes the length to exceed       *  max_size(), length_error is thrown.  If @a pos1 is beyond the end of       *  this string or @a pos2 is beyond the end of @a str, out_of_range is       *  thrown.  The value of the string doesn't change if an error is       *  thrown.      */      basic_string&      insert(size_type __pos1, const basic_string& __str,	     size_type __pos2, size_type __n)      { return this->insert(__pos1, __str._M_data()			    + __str._M_check(__pos2, "basic_string::insert"),			    __str._M_limit(__pos2, __n)); }      /**       *  @brief  Insert a C substring.       *  @param pos  Iterator referencing location in string to insert at.       *  @param s  The C string to insert.       *  @param n  The number of characters to insert.       *  @return  Reference to this string.       *  @throw  std::length_error  If new length exceeds @c max_size().       *  @throw  std::out_of_range  If @a pos is beyond the end of this       *  string.       *       *  Inserts the first @a n characters of @a s starting at @a pos.  If       *  adding characters causes the length to exceed max_size(),       *  length_error is thrown.  If @a pos is beyond end(), out_of_range is       *  thrown.  The value of the string doesn't change if an error is       *  thrown.      */      basic_string&      insert(size_type __pos, const _CharT* __s, size_type __n);      /**       *  @brief  Insert a C string.       *  @param pos  Iterator referencing location in string to insert at.       *  @param s  The C string to insert.       *  @return  Reference to this string.       *  @throw  std::length_error  If new length exceeds @c max_size().       *  @throw  std::out_of_range  If @a pos is beyond the end of this       *  string.       *       *  Inserts the first @a n characters of @a s starting at @a pos.  If       *  adding characters causes the length to exceed max_size(),       *  length_error is thrown.  If @a pos is beyond end(), out_of_range is       *  thrown.  The value of the string doesn't change if an error is       *  thrown.      */      basic_string&      insert(size_type __pos, const _CharT* __s)      {	__glibcxx_requires_string(__s);	return this->insert(__pos, __s, traits_type::length(__s));      }      /**       *  @brief  Insert multiple characters.       *  @param pos  Index in string to insert at.       *  @param n  Number of characters to insert       *  @param c  The character to insert.       *  @return  Reference to this string.       *  @throw  std::length_error  If new length exceeds @c max_size().       *  @throw  std::out_of_range  If @a pos is beyond the end of this       *  string.       *       *  Inserts @a n copies of character @a c starting at index @a pos.  If       *  adding characters causes the length to exceed max_size(),       *  length_error is thrown.  If @a pos > length(), out_of_range is       *  thrown.  The value of the string doesn't change if an error is       *  thrown.