Difference between revisions of "cpp/iterator/size"
From cppreference.com
(→Notes: +) |
(Corrected inconsistent formatting by adding a newline before a '{') |
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constexpr auto ssize(const C& c) | constexpr auto ssize(const C& c) | ||
-> std::common_type_t<std::ptrdiff_t, | -> std::common_type_t<std::ptrdiff_t, | ||
| − | std::make_signed_t<decltype(c.size())>> { | + | std::make_signed_t<decltype(c.size())>> |
| + | { | ||
using R = std::common_type_t<std::ptrdiff_t, | using R = std::common_type_t<std::ptrdiff_t, | ||
std::make_signed_t<decltype(c.size())>>; | std::make_signed_t<decltype(c.size())>>; | ||
Revision as of 10:13, 26 November 2019
| Defined in header <iterator>
|
||
| template <class C> constexpr auto size(const C& c) -> decltype(c.size()); |
(1) | (since C++17) |
| template <class C> constexpr auto ssize(const C& c) |
(2) | (since C++20) |
| template <class T, std::size_t N> constexpr std::size_t size(const T (&array)[N]) noexcept; |
(3) | (since C++17) |
| template <class T, std::ptrdiff_t N> constexpr std::ptrdiff_t ssize(const T (&array)[N]) noexcept; |
(4) | (since C++20) |
Returns the size of the given container c or array array.
1-2) Returns
c.size(), converted to the return type if necessary.3-4) Returns
N.Contents |
Parameters
| c | - | a container with a size method
|
| array | - | an array of arbitrary type |
Return value
The size of c or array
Notes
In addition to being included in <iterator>, std::size and std::ssize are guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <span>(since C++20), <string>, <string_view>, <unordered_map>, <unordered_set>, and <vector>.
Possible implementation
| First version |
|---|
template <class C> constexpr auto size(const C& c) -> decltype(c.size()) { return c.size(); } |
| Second version |
template <class C> constexpr auto ssize(const C& c) -> std::common_type_t<std::ptrdiff_t, std::make_signed_t<decltype(c.size())>> { using R = std::common_type_t<std::ptrdiff_t, std::make_signed_t<decltype(c.size())>>; return static_cast<R>(c.size()); } |
| Third version |
template <class T, std::size_t N> constexpr std::size_t size(const T (&array)[N]) noexcept { return N; } |
| Fourth version |
template <class T, std::ptrdiff_t N> constexpr std::ptrdiff_t ssize(const T (&array)[N]) noexcept { return N; } |
Example
Run this code
#include <iostream> #include <vector> #include <iterator> int main() { std::vector<int> v = { 3, 1, 4 }; std::cout << std::size(v) << '\n'; int a[] = { -5, 10, 15 }; std::cout << std::size(a) << '\n'; }
Output:
3 3
