std::basic_string::reserve
From cppreference.com
< cpp | string | basic string
void reserve( size_type new_cap = 0 ); |
||
Informs a std::basic_string
object of a planned change in size, so that it can manage the storage allocation appropriately.
- If
new_cap
is greater than the current capacity(), new storage is allocated, and capacity() is made equal or greater thannew_cap
.
- If
new_cap
is less than the current capacity(), this is a non-binding shrink request.
- If
new_cap
is less than the current size(), this is a non-binding shrink-to-fit request equivalent to shrink_to_fit() (since C++11).
If a capacity change takes place, all iterators and references, including the past-the-end iterator, are invalidated.
Parameters
new_cap | - | new capacity of the string |
Return value
(none)
Exceptions
Throws std::length_error if new_cap
is greater than max_size()
May throw any exceptions thrown by std::allocator_traits<Allocator>::allocate(), such as std::bad_alloc.
Complexity
At most linear in the size() of the string
Example
Run this code
#include <cassert> #include <string> int main() { std::string s; std::string::size_type new_capacity{ 100u }; assert(new_capacity > s.capacity()); s.reserve(new_capacity); assert(new_capacity <= s.capacity()); }
See also
returns the number of characters that can be held in currently allocated storage (public member function) |