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

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

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Containers library

Iterators library

Ranges library (C++20)

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Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

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

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 integral type.	(until C++11)
This overload only participates in overload resolution if InputIt qualifies as a 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 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 guarantee	added strong exception safety guarantee
LWG 2946	C++17	overload (8) causes ambiguity in some cases	avoided by making it a template

See also

append_range (C++23)	appends a range of characters to the end (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)
wcsncat	appends a certain amount of wide characters from one wide string to another (function)