std::basic_string<CharT,Traits,Allocator>::operator+=
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basic_string::operator+=
(C++23)
(C++20)
(C++20)
(C++23)
(C++20)(C++20)
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(C++11)(C++11)
(C++14)
(C++11)
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) basic_string& operator+=( const StringViewLike& t );
(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.
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.
std::basic_string_view <CharT, Traits>> is true and std::is_convertible_v <const StringViewLike&, const CharT*> is false.
Contents
[edit] 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
[edit] Return value
*this
[edit] Complexity
There are no standard complexity guarantees, typical implementations behave similar to std::vector::insert().
[edit] 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).
[edit] 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.
[edit] 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"
[edit] 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 |