std::basic_string::append(3)

NAME
std::basic_string::append - std::basic_string::append

Synopsis
   basic_string& append( size_type count, CharT (1) (constexpr since
   ch ); C++20)
   basic_string& append( const basic_string& str (2) (constexpr since
   ); C++20)
   basic_string& append( const basic_string& str,
                        size_type pos, size_type (until C++14)
   count );
   basic_string& append( const basic_string& str, (since C++14)
                        size_type pos, size_type (constexpr since
   count = npos ); C++20)
   basic_string& append( const CharT* s, (4) (constexpr since
   size_type count ); C++20)
   basic_string& append( const CharT* s ); (5) (constexpr since
                        C++20)
   template< class InputIt > (constexpr since
   basic_string& append( InputIt first, InputIt (6) C++20)
   last ); (3)
   basic_string& append( (since C++11)
   std::initializer_list<CharT> ilist ); (7) (constexpr since
                        C++20)
   template< class StringViewLike > (since C++17)
   basic_string& append( const StringViewLike& t (8) (constexpr since
   ); C++20)
   template< class StringViewLike >
                        (since C++17)
   basic_string& append( const StringViewLike& t, (9) (constexpr since
                        C++20)
                        size_type pos, size_type
   count = npos );
   Appends additional characters to the string.
   1) Appends count copies of character ch.
   2) Appends string str.
   3) Appends a substring [pos, pos + count) of str.
     * If the requested substring lasts past the end of the string, or if count ==
       npos, the appended substring is [pos, size()).
     * If pos > str.size(), std::out_of_range is thrown.
   4) Appends characters in the range [s, s + count). This range can contain null
   characters.
   If [s, s + count) is not a valid range, the behavior is undefined.
   5) Appends the null-terminated character string pointed to by s, as if by append(s,
   Traits::length(s)).
   6) Appends characters in the range [first, last).
   This overload has the same effect as overload (1) if InputIt is an (until C++11)
   integral type.
   This overload only participates in overload resolution if InputIt (since C++11)
   qualifies as a LegacyInputIterator.
   7) Appends characters from the initializer list ilist.
   8) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT,
   Traits> sv = t;, then appends all characters from sv as if by append(sv.data(),
   sv.size()).
   This overload participates in overload resolution only if
   std::is_convertible_v<const StringViewLike&,
                        std::basic_string_view<CharT, Traits>> is true and
   std::is_convertible_v<const StringViewLike&, const CharT*> is false.
   9) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT,
   Traits> sv = t;, then appends the characters from the subview [pos, pos + count) of
   sv.
     * If the requested subview extends past the end of sv, or if count == npos, the
       appended subview is [pos, sv.size()).
     * If pos >= sv.size(), std::out_of_range is thrown.
   This overload participates in overload resolution only if
   std::is_convertible_v<const StringViewLike&,
                        std::basic_string_view<CharT, Traits>> is true and
   std::is_convertible_v<const StringViewLike&, const CharT*> is false.

Parameters
   count - number of characters to append
   pos - the index of the first character to append
   ch - character value to append
   first, last - range of characters to append
   str - string to append
   s - pointer to the character string to append
   ilist - initializer list with the characters to append
   t - object convertible to std::basic_string_view with the characters to
                 append

Return value
   *this

Complexity
   There are no standard complexity guarantees, typical implementations behave similar
   to std::vector::insert().

Exceptions
   If the operation would result in size() > max_size(), throws std::length_error.
   If an exception is thrown for any reason, this function has no effect (strong
   exception safety guarantee).

Example
// Run this code
 #include <iostream>
 #include <string>
 int main()
 {
     std::basic_string<char> str = "string";
     const char* cptr = "C-string";
     const char carr[] = "Two and one";
     std::string output;
     // 1) Append a char 3 times.
     // Notice, this is the only overload accepting chars.
     output.append(3, '*');
     std::cout << "1) " << output << '\n';
     // 2) Append a whole string
     output.append(str);
     std::cout << "2) " << output << '\n';
     // 3) Append part of a string (last 3 letters, in this case)
     output.append(str, 3, 3);
     std::cout << "3) " << output << '\n';
     // 4) Append part of a C-string
     // Notice, because `append` returns *this, we can chain calls together
     output.append(1, ' ').append(carr, 4);
     std::cout << "4) " << output << '\n';
     // 5) Append a whole C-string
     output.append(cptr);
     std::cout << "5) " << output << '\n';
     // 6) Append range
     output.append(&carr[3], std::end(carr));
     std::cout << "6) " << output << '\n';
     // 7) Append initializer list
     output.append({' ', 'l', 'i', 's', 't'});
     std::cout << "7) " << output << '\n';
 }

Output:
 1) ***
 2) ***string
 3) ***stringing
 4) ***stringing Two
 5) ***stringing Two C-string
 6) ***stringing Two C-string and one
 7) ***stringing Two C-string and one list
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 847 C++98 there was no exception safety added strong exception safety
                       guarantee guarantee
   LWG 2946 C++17 overload (8) causes ambiguity in avoided by making it a
                       some cases template

See also
   append_range appends a range of characters to the end
   (C++23) (public member function)
   operator+= appends characters to the end
                (public member function)
   strcat concatenates two strings
                (function)
   strncat concatenates a certain amount of characters of two strings
                (function)
   wcscat appends a copy of one wide string to another
                (function)
                appends a certain amount of wide characters from one wide string to
   wcsncat another
                (function)