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

 

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Strings library

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) Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of

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 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*) Operations basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr

Constants basic_string::npos Non-member functions operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversions stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11)  stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Literals operator""s (C++14) Helper classes hash<std::basic_string> (C++11) Deduction guides(C++17)

 

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)

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";constchar* cptr ="C-string";constchar 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

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)