std::basic_string::reserve - cppreference.com

##### cppreference.com

##### Search

Create account

##### Namespaces

- Page
- Discussion

##### Variants

##### Views

- View
- Edit
- History

##### Actions

# 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 than `new_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.

### [edit] Parameters

new_cap | - | new capacity of the string

### [edit] Return value

(none)

### [edit] 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.

### [edit] Complexity

At most linear in the size() of the string

### [edit] 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());
    }

### [edit] See also

capacity | returns the number of characters that can be held in currently allocated storage (public member function) [edit]

Retrieved from "http://en.cppreference.com/mwiki/index.php?title=cpp/string/basic_string/reserve&oldid=72361"