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    std::basic_string<CharT,Traits,Allocator>::append

    From cppreference.com
     
    C++
     
    Strings library
     
    std::basic_string
     
    basic_string& append( size_type count, CharT ch );
    		 (1) (constexpr since C++20)
    basic_string& append( const CharT* s, size_type count );
    		 (2) (constexpr since C++20)
    basic_string& append( const CharT* s );
    		 (3) (constexpr since C++20)
    template< class SV > basic_string& append( const SV& t );
    		 (4) (since C++17)
    (constexpr since C++20)
    template< class SV > basic_string& append( const SV& t, size_type pos, size_type count = npos );
    		 (5) (since C++17)
    (constexpr since C++20)
    basic_string& append( const basic_string& str );
    		 (6) (constexpr since C++20)
    (7)
    basic_string& append( const basic_string& str, size_type pos, size_type count );
    		 (until C++14)
    basic_string& append( const basic_string& str, size_type pos, size_type count = npos );
    		 (since C++14)
    (constexpr since C++20)
    template< class InputIt > basic_string& append( InputIt first, InputIt last );
    		 (8) (constexpr since C++20)
    basic_string& append( std::initializer_list<CharT> ilist );
    		 (9) (since C++11)
    (constexpr since C++20)
    See More

    Appends additional characters to the string.

    1) Appends count copies of character ch.
    2) Appends characters in the range [s, s + count).
    If [s, s + count) is not a valid range, the behavior is undefined.
    3) Equivalent to return append(s, Traits::length(s));.
    4,5) Appends characters in a string view sv constructed from t.
    • If only t is provided, all characters in sv are appended.
    • If pos is also provided:
      • If count is npos, all characters in sv starting from pos are appended.
      • Otherwise, the std::min(count, sv.size() - pos) characters in sv starting from pos are appended.
    These overloads participate in overload resolution only if all following conditions are satisfied:
    • std::is_convertible_v<const SV&, std::basic_string_view<CharT, Traits>> is true.
    • std::is_convertible_v<const SV&, const CharT*> is false.
    4) Equivalent to std::basic_string_view<CharT, Traits> sv = t;
    return append(sv.data(), sv.size());    .
    5) Equivalent to std::basic_string_view<CharT, Traits> sv = t;
    return append(sv.substr(pos, count));    .
    6,7) Appends characters in another string str.
    • If only str is provided, all characters in it are appended.
    • If pos is also provided:
      • If count is npos, all characters in str starting from pos are appended.
      • Otherwise, the std::min(count, str.size() - pos) characters in str starting from pos are appended.
    6) Equivalent to return append(str.data(), str.size());.
    7) Equivalent to return append(std::basic_string_view<CharT, Traits>
    (str).substr(pos, count));    .
    		(since C++20)
    8) Equivalent to return append(basic_string(first, last, get_allocator()));.

    This overload has the same effect as overload (1) if InputIt is an integral type.

    		(until C++11)

    This overload participates in overload resolution only if InputIt satisfies the requirements of LegacyInputIterator.

    		(since C++11)
    9) Equivalent to return append(ilist.begin(), ilist.size());.

    Parameters

    count - number of characters to append
    ch - character value to append
    s - pointer to the character string to append
    t - object convertible to std::basic_string_view with the characters to append
    pos - the index of the first character to append
    str - string to append
    first, last - range of characters to append
    ilist - initializer list 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 cause size() to exceed max_size(), throws std::length_error.

    5) If pos > sv.size() is true, throws std::out_of_range.
    7) If pos > str.size() is true, throws std::out_of_range.

    If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

    Example

    Run this code
    #include <cassert>
#include <string>

int main()
{
    std::string str = "std::string";
    const char* cptr = "C-string";
    const char carr[] = "range";

    std::string result;

    // 1) Append a char 3 times.
    // Note: This is the only overload accepting “CharT”s.
    result.append(3, '*');
    assert(result == "***");

    // 2) Append a fixed-length C-string
    result.append(cptr, 5);
    assert(result == "***C-str");

    // 3) Append a null-terminated C-string
    // Note: Because “append” returns *this, we can chain calls together.
    result.append(1, ' ').append(cptr);
    assert(result == "***C-str C-string");

    // 6) Append a whole string
    result.append(1, ' ').append(str);
    assert(result == "***C-str C-string std::string");

    // 7) Append part of a string
    result.append(str, 3, 2);
    assert(result == "***C-str C-string std::string::");

    // 8) Append range
    result.append(&carr[2], &carr[3]);
    assert(result == "***C-str C-string std::string::n");

    // 9) Append initializer list
    result.append({'p', 'o', 's'});
    assert(result == "***C-str C-string std::string::npos");
}

    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 guarantee added strong exception safety guarantee
    LWG 2250 C++98 the behavior of overload (7) was
    undefined if pos > str.size() is true     		always throws an exception in this case
    LWG 2788 C++98 overload (8) used a default constructed
    allocator to construct the temporary string     		obtains the allocator
    from get_allocator()
    LWG 2946 C++17 overload (4) causes ambiguity in some cases avoided by making it a template

    See also

    (C++23)
    		 appends a range of characters to the end
    (public member function) [edit]
    		appends characters to the end
    (public member function) [edit]
    		concatenates two strings
    (function) [edit]
    		concatenates a certain amount of characters of two strings
    (function) [edit]
    		appends a copy of one wide string to another
    (function) [edit]
    		appends a certain amount of wide characters from one wide string to another
    (function) [edit]