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deductionguidesforstd::vector(3) C++ Standard Libary deductionguidesforstd::vector(3)


deductionguidesforstd::vector - deductionguidesforstd::vector


Defined in header <vector>
template< class InputIt,

class Alloc = std::allocator<typename
std::iterator_traits<InputIt>::value_type>> (since C++17)
vector(InputIt, InputIt, Alloc = Alloc())

-> vector<typename std::iterator_traits<InputIt>::value_type, Alloc>;

This deduction guide is provided for vector to allow deduction from an iterator
range. This overload participates in overload resolution only if InputIt satisfies
LegacyInputIterator and Alloc satisfies Allocator.

Note: the extent to which the library determines that a type does not satisfy
LegacyInputIterator is unspecified, except that as a minimum integral types do not
qualify as input iterators. Likewise, the extent to which it determines that a type
does not satisfy Allocator is unspecified, except that as a minimum the member type
Alloc::value_type must exist and the expression
std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as
an unevaluated operand.


// Run this code

#include <vector>

int main() {
std::vector<int> v = {1, 2, 3, 4};

// uses explicit deduction guide to deduce std::vector<int>
std::vector x(v.begin(), v.end());

// deduces std::vector<std::vector<int>::iterator>
// first phase of overload resolution for list-initialization selects the candidate
// synthesized from the initializer-list constructor; second phase is not performed and
// deduction guide has no effect
std::vector y{v.begin(), v.end()};