std::vector<T,Allocator>::clear
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Containers library
(C++17)
(C++11)
(C++26)
(C++26)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++23)
(C++23)
(C++23)
(C++23)
(C++20)
(C++23)
Tables
std::vector
Non-member functions
Deduction guides (C++17)
(C++23)
(C++11)
(C++11)
(C++11)
(C++11)
(DR*)
vector::clear
(C++23)
(C++23)
(C++11)
(C++11)
(C++20)
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
void clear();
(noexcept since C++11) (constexpr since C++20)
Erases all elements from the container. After this call, size() returns zero.
Invalidates any references, pointers, and iterators referring to contained elements. Any past-the-end iterators are also invalidated.
[edit] Complexity
Linear in the size of the container, i.e., the number of elements.
Notes
Calling clear() does not affect the result of capacity() . The standard's restriction on the changes to capacity is in the specification of reserve() , see SO.
[edit] Example
Run this code
#include <iostream> #include <string_view> #include <vector> void print_info(std::string_view rem, const std::vector <int>& v) { std::cout << rem << "{ "; for (const auto& value : v) std::cout << value << ' '; std::cout << "}\n"; std::cout << "Size=" << v.size() << ", Capacity=" << v.capacity() << '\n'; } int main() { std::vector <int> container{1, 2, 3}; print_info("Before clear: ", container); container.clear(); print_info("After clear: ", container); }
Output:
Before clear: { 1 2 3 }
Size=3, Capacity=3
After clear: { }
Size=0, Capacity=3Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2231 | C++11 | complexity guarantee was mistakenly omitted in C++11 | complexity reaffirmed as linear |