std::basic_string<CharT,Traits,Allocator>::operator+=

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

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& operator+=(const basic_string& str );	(1)	(constexpr since C++20)
basic_string& operator+=( CharT ch );	(2)	(constexpr since C++20)
basic_string& operator+=(const CharT* s );	(3)	(constexpr since C++20)
basic_string& operator+=(std::initializer_list<CharT> ilist );	(4)	(since C++11) (constexpr since C++20)
template<class StringViewLike > basic_string& operator+=(const StringViewLike& t );	(5)	(since C++17) (constexpr since C++20)

Appends additional characters to the string.

1) Appends string str.

2) Appends character ch.

3) Appends the null-terminated character string pointed to by s.

4) Appends characters in the initializer list ilist.

5) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then appends characters in the string view sv as if by append(sv).

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

str	-	string to append
ch	-	character value to append
s	-	pointer to a null-terminated character string to append
ilist	-	std::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 cause size() to exceed max_size(), throws std::length_error.

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

Notes

Overload (2) can accept any types that are implicitly convertible to CharT. For std::string, where CharT is char, the set of acceptable types includes all arithmetic types. This may have unintended effects.

Example

Run this code

#include <iomanip>#include <iostream>#include <string>   int main(){std::string str;   // reserve sufficient storage space to avoid memory reallocation str.reserve(50);   std::cout<<std::quoted(str)<<'\n';// empty string   str +="This";std::cout<<std::quoted(str)<<'\n';   str +=std::string(" is ");std::cout<<std::quoted(str)<<'\n';   str +='a';std::cout<<std::quoted(str)<<'\n';   str +={' ', 's', 't', 'r', 'i', 'n', 'g', '.'};std::cout<<std::quoted(str)<<'\n';   str +=69.96;// Equivalent to str += static_cast<char>(69.96);// 'E' (ASCII code 69) is appended by overload (2),// which might not be the intent.   // To add a numeric value, consider std::to_string(): str +=std::to_string(1729);   std::cout<<std::quoted(str)<<'\n';}

Output:

"" "This" "This is " "This is a" "This is a string." "This is a string.E1729"

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 (5) caused ambiguity in some cases	avoided by making it a template

See also

append

appends characters to the end (public member function)