Difference between revisions of "cpp/container/vector/begin"
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Latest revision as of 06:56, 7 November 2021
| iterator begin(); |
(1) | (noexcept since C++11) (constexpr since C++20) |
| const_iterator begin() const; |
(2) | (noexcept since C++11) (constexpr since C++20) |
| const_iterator cbegin() const noexcept; |
(3) | (since C++11) (constexpr since C++20) |
Returns an iterator to the first element of the vector.
If the vector is empty, the returned iterator will be equal to end().
Contents |
[edit] Parameters
(none)
[edit] Return value
Iterator to the first element.
[edit] Complexity
Constant.
Notes
libc++ backports cbegin() to C++98 mode.
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <numeric> #include <string> #include <vector> int main() { std::vector<int> nums{1, 2, 4, 8, 16}; std::vector<std::string> fruits{"orange", "apple", "raspberry"}; std::vector<char> empty; // Print vector. std::for_each(nums.begin(), nums.end(), [](const int n) { std::cout << n << ' '; }); std::cout << '\n'; // Sums all integers in the vector nums (if any), printing only the result. std::cout << "Sum of nums: " << std::accumulate(nums.begin(), nums.end(), 0) << '\n'; // Prints the first fruit in the vector fruits, checking if there is any. if (!fruits.empty()) std::cout << "First fruit: " << *fruits.begin() << '\n'; if (empty.begin() == empty.end()) std::cout << "vector 'empty' is indeed empty.\n"; }
Output:
1 2 4 8 16 Sum of nums: 31 First fruit: orange vector 'empty' is indeed empty.
[edit] See also
| (C++11) |
returns an iterator to the end (public member function) |
| (C++11)(C++14) |
returns an iterator to the beginning of a container or array (function template) |
