NAME

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

Synopsis

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

constexpr basic_string& (since append( const C++20) StringViewLike& t,

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.
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 (until C++11)
integral type.
This overload only participates in overload resolution if InputIt (since C++11)
qualifies as an 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 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 avoided by making it a
some cases 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