std::basic_string::reserve

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos

Non-member functions operator+ operator==operator!=operator<operator>operator<=operator>= swap(std::basic_string) operator<<operator>> getline stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string> (C++11)(C++11)(C++11)(C++11)

 

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.

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

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