std::basic_string<CharT,Traits,Allocator>::operator+=
(1) | ||
basic_string& operator+=( const basic_string& str ); |
(until C++20) | |
constexpr basic_string& operator+=( const basic_string& str ); |
(since C++20) | |
(2) | ||
basic_string& operator+=( CharT ch ); |
(until C++20) | |
constexpr basic_string& operator+=( CharT ch ); |
(since C++20) | |
(3) | ||
basic_string& operator+=( const CharT* s ); |
(until C++20) | |
constexpr basic_string& operator+=( const CharT* s ); |
(since C++20) | |
(4) | ||
basic_string& operator+=( std::initializer_list<CharT> ilist ); |
(since C++11) (until C++20) |
|
constexpr basic_string& operator+=( std::initializer_list<CharT> ilist ); |
(since C++20) | |
(5) | ||
template < class StringViewLike > basic_string& operator+=( const StringViewLike& t ); |
(since C++17) (until C++20) |
|
template < class StringViewLike > constexpr basic_string& operator+=( const StringViewLike& t ); |
(since C++20) |
Appends additional characters to the string.
str
ch
s
.
ilist
.
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 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
.
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.
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 some cases |
avoided by making it a template |
Example
#include <iostream> #include <iomanip> #include <string> int main() { std::string str; str.reserve(50); //reserves sufficient storage space to avoid memory reallocation 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 += 76.85; // equivalent to str += static_cast<char>(76.85), might not be the intent std::cout << std::quoted(str) << '\n'; }
Output:
"" "This" "This is " "This is a" "This is a string." "This is a string.L"
See also
appends characters to the end (public member function) |
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