Difference between revisions of "cpp/container/vector/assign"
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Revision as of 06:42, 10 August 2020
void assign( size_type count, const T& value ); |
(1) | (constexpr since C++20) |
template< class InputIt > void assign( InputIt first, InputIt last ); |
(2) | (constexpr since C++20) |
void assign( std::initializer_list<T> ilist ); |
(3) | (since C++11) (constexpr since C++20) |
Replaces the contents of the container.
1) Replaces the contents with count copies of value value.
2) Replaces the contents with copies of those in the range
[first, last). If either argument is an iterator into *this, the behavior is undefined.
|
This overload has the same effect as overload (1) if |
(until C++11) |
|
This overload participates in overload resolution only if |
(since C++11) |
3) Replaces the contents with the elements from ilist.
All iterators (including the end() iterator) and all references to the elements are invalidated.
Contents |
Parameters
| count | - | the new size of the container |
| value | - | the value to initialize elements of the container with |
| first, last | - | the range to copy the elements from |
| ilist | - | std::initializer_list to copy the values from |
Complexity
1) Linear in count.
2) Linear in distance between first and last.
3) Linear in ilist.size().
Example
The following code uses assign to add several characters to a std::vector<char>:
Run this code
#include <vector> #include <iostream> #include <string> int main() { std::vector<char> characters; auto print_vector = [&]() { for (char c : characters) std::cout << c << ' '; std::cout << '\n'; }; characters.assign(5, 'a'); print_vector(); const std::string extra(6, 'b'); characters.assign(extra.begin(), extra.end()); print_vector(); characters.assign({'C', '+', '+', '1', '1'}); print_vector(); }
Output:
a a a a a b b b b b b C + + 1 1
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 2209 | C++98 | the replacement operation was required to be implemented as erasing all existing elements followed by inserting the given elements |
removed the requirement |
See also
| (C++23) |
assigns a range of values to the container (public member function) |
| assigns values to the container (public member function) |
