std::vector::resize
void resize( size_type count, T value = T() ); |
(until C++11) | |
void resize( size_type count ); |
(1) | (since C++11) |
void resize( size_type count, const value_type& value ); |
(2) | (since C++11) |
Resizes the container to contain count
elements.
If the current size is greater than count
, the container is reduced to its first count
elements.
If the current size is less than |
(until C++11) |
If the current size is less than 1) additional default-inserted elements are appended
2) additional copies of value are appended
|
(since C++11) |
Parameters
count | - | new size of the container |
value | - | the value to initialize the new elements with |
Type requirements | ||
-T must meet the requirements of MoveInsertable and DefaultInsertable in order to use overload (1).
| ||
-T must meet the requirements of CopyInsertable in order to use overload (2).
|
Return value
(none)
Complexity
Linear in the difference between the current size and count
. Additional complexity possible due to reallocation if capacity is less than count
Exceptions
If an exception is thrown, this function has no effect (strong exception guarantee).
In overload (1), if T 's move constructor is not noexcept and T is not CopyInsertable into *this , vector will use the throwing move constructor. If it throws, the guarantee is waived and the effects are unspecified. |
(since C++11) |
Notes
If value-initialization in overload (1) is undesirable, for example, if the elements are of non-class type and zeroing out is not needed, it can be avoided by providing a custom Allocator::construct.
Vector capacity is never reduced when resizing to smaller size because that would invalidate all iterators, rather than only the ones that would be invalidated by the equivalent sequence of pop_back() calls.
Example
#include <iostream> #include <vector> int main() { std::vector<int> c = {1, 2, 3}; std::cout << "The vector holds: "; for(auto& el: c) std::cout << el << ' '; std::cout << '\n'; c.resize(5); std::cout << "After resize up to 5: "; for(auto& el: c) std::cout << el << ' '; std::cout << '\n'; c.resize(2); std::cout << "After resize down to 2: "; for(auto& el: c) std::cout << el << ' '; std::cout << '\n'; }
Output:
The vector holds: 1 2 3 After resize up to 5: 1 2 3 0 0 After resize down to 2: 1 2
See also
returns the number of elements (public member function) | |
inserts elements (public member function) | |
erases elements (public member function) |