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

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< cpp‎ | string‎ | basic string

basic_string& append( size_type count, CharT ch ); | (1) |
basic_string& append( const basic_string& str ); | (2) |
| (3) |
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)
basic_string& append( const CharT* s, size_type count ); | (4) |
basic_string& append( const CharT* s ); | (5) |
template< class InputIt > basic_string& append( InputIt first, InputIt last ); | (6) |
basic_string& append( std::initializer_list<CharT> ilist ); | (7) | (since C++11)
template < class T > basic_string& append( const T& t ); | (8) | (since C++17)
template < class T > basic_string& append( const T& t, size_type pos, size_type count = npos ); | (9) | (since C++17)

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.
5) Appends the null-terminated character string pointed to by `s`. The length of the string is determined by the first null character using Traits::length(s).
6) Appends characters in the range `[first, last)`.

This overload has the same effect as overload (1) if `InputIt` is an integral type. | (until C++11)
This overload only participates in overload resolution if `InputIt` qualifies as an LegacyInputIterator | (since C++11)

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 only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, 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 only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, 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 an exception is thrown for any reason, this function has no effect (strong exception guarantee). (since C++11)

If the operation would result in `size() > max_size()`, throws std::length_error.

### 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 2946 | C++17 | `string_view` overload causes ambiguity in some cases | avoided by making it a template

### Example

Run this code

    #include <string>
    #include <iostream>

    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

### See also

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)
wcsncat | appends a certain amount of wide characters from one wide string to another (function)

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