std::basic_string<CharT,Traits,Allocator>::operator+=
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< cpp | string | basic string
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.
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 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).
[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 |
[edit] See also
appends characters to the end (public member function) |