std::unordered_set<Key,Hash,KeyEqual,Allocator>::begin,std::unordered_set<Key,Hash,KeyEqual,Allocator>::cbegin
From cppreference.com
<cpp |container |unordered set
C++
Containers library
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| Sequence | ||||
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(C++26) | ||||
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| Associative | ||||
| Unordered associative | ||||
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(C++11) | ||||
(C++11) | ||||
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| Adaptors | ||||
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| Views | ||||
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| Tables | ||||
| Iterator invalidation | ||||
| Member function table | ||||
| Non-member function table |
std::unordered_set| Member types | ||||||
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| Deduction guides(C++17) | ||||||
iterator begin()noexcept; | (1) | (since C++11) (constexpr since C++26) |
const_iterator begin()constnoexcept; | (2) | (since C++11) (constexpr since C++26) |
const_iterator cbegin()constnoexcept; | (3) | (since C++11) (constexpr since C++26) |
Returns an iterator to the first element of*this.
If*this is empty, the returned iterator will be equal toend().
Contents |
[edit]Return value
Iterator to the first element.
[edit]Complexity
Constant.
Notes
Because bothiterator andconst_iterator are constant iterators (and may in fact be the same type), it is not possible to mutate the elements of the container through an iterator returned by any of these member functions.
[edit]Example
Run this code
#include <iostream>#include <unordered_set> struct Point{double x, y;}; int main(){ Point pts[3]={{1,0},{2,0},{3,0}}; // points is a set containing the addresses of pointsstd::unordered_set<Point*> points={ pts, pts+1, pts+2}; // Change each y-coordinate of (i, 0) from 0 into i^2 and print the pointfor(auto iter= points.begin(); iter!= points.end();++iter){(*iter)->y=((*iter)->x)*((*iter)->x);// iter is a pointer-to-Point*std::cout<<"("<<(*iter)->x<<", "<<(*iter)->y<<") ";}std::cout<<'\n'; // Now using the range-based for loop, we increase each y-coordinate by 10for(Point* i: points){ i->y+=10;std::cout<<"("<< i->x<<", "<< i->y<<") ";}}
Possible output:
(3, 9) (1, 1) (2, 4) (3, 19) (1, 11) (2, 14)
[edit]See also
| returns an iterator to the end (public member function)[edit] | |
(C++11)(C++14) | returns an iterator to the beginning of a container or array (function template)[edit] |
