public member function
<deque>
std::deque::emplace_front
template <class... Args>
void emplace_front (Args&&... args);
Construct and insert element at beginning
Inserts a new element at the beginning of the deque, right before its current first element. This new element is constructed in place using args as the arguments for its construction.
This effectively increases the container size by one.
The element is constructed in-place by calling allocator_traits::construct with args forwarded.
A similar member function exists, push_front, which either copies or moves an existing object into the container.
Parameters
- args
- Arguments forwarded to construct the new element.
Return value
none.
The storage for the new element is allocated using allocator_traits<allocator_type>::construct(), which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Example
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// deque::emplace_from
#include <iostream>
#include <deque>
int main ()
{
std::deque<int> mydeque = {10,20,30};
mydeque.emplace_front (111);
mydeque.emplace_front (222);
std::cout << "mydeque contains:";
for (auto& x: mydeque)
std::cout << ' ' << x;
std::cout << '\n';
return 0;
}
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Output:
mydeque contains: 222 111 10 20 30
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Iterator validity
All iterators related to this container are invalidated, but pointers and references remain valid, referring to the same elements they were referring to before the call.
Data races
The container is modified.
No contained elements are accessed by the call: concurrently accessing or modifying them is safe (although see iterator validity above).
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.
If allocator_traits::construct is not supported with the appropriate arguments, it causes undefined behavior.