std::basic_string<CharT,Traits,Allocator>::operator+=
< cpp | string | basic string
basic_string& operator+=( const basic_string& str ); |
(1) | |
basic_string& operator+=( CharT ch ); |
(2) | |
basic_string& operator+=( const CharT* s ); |
(3) | |
basic_string& operator+=( std::initializer_list<CharT> ilist ); |
(4) | (since C++11) |
template < class T > basic_string& operator+=( const T& t ); |
(5) | (since C++17) |
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 only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, 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
1) linear in size of
str
2) constant
3) linear in size of
s
4) linear in size of
ilist
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
Run this code
#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) |