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)