Difference between revisions of "cpp/iterator/size"
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===Notes=== | ===Notes=== | ||
In addition to being included in {{tt|<iterator>}}, {{tt|std::size}} is guaranteed to become available if any of the following headers are included: {{tt|<array>}}, {{tt|<deque>}}, {{tt|<forward_list>}}, {{tt|<list>}}, {{tt|<map>}}, {{tt|<regex>}}, {{tt|<set>}}, {{tt|<string>}}, {{tt|<unordered_map>}}, {{tt|<unordered_set>}}, and {{tt|<vector>}}. | In addition to being included in {{tt|<iterator>}}, {{tt|std::size}} is guaranteed to become available if any of the following headers are included: {{tt|<array>}}, {{tt|<deque>}}, {{tt|<forward_list>}}, {{tt|<list>}}, {{tt|<map>}}, {{tt|<regex>}}, {{tt|<set>}}, {{tt|<string>}}, {{tt|<unordered_map>}}, {{tt|<unordered_set>}}, and {{tt|<vector>}}. | ||
| + | |||
| + | ===Possible implementation=== | ||
| + | {{eq fun | ||
| + | | 1= | ||
| + | template <class C> | ||
| + | constexpr auto size(const C& c) -> decltype(c.size()) | ||
| + | { | ||
| + | return c.size(); | ||
| + | } | ||
| + | | 2= | ||
| + | template <class T, std::size_t N> | ||
| + | constexpr std::size_t size(T (&array)[N]) noexcept | ||
| + | { | ||
| + | return N; | ||
| + | } | ||
| + | }} | ||
===Example=== | ===Example=== | ||
Revision as of 03:34, 10 April 2015
| Defined in header <iterator>
|
||
| template < class C > constexpr auto size( const C& c ) -> decltype(c.size()); |
(1) | (since C++17) |
| template < class T, size_t N > constexpr size_t size( const T (&array)[N] ) noexcept; |
(2) | (since C++17) |
Returns the size of the given container c or array array.
1) Returns
c.size().2) 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
Exceptions
2)
noexcept specification:
noexcept
Notes
In addition to being included in <iterator>, std::size is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <string>, <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 T, std::size_t N> constexpr std::size_t size(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
