public member function
<list>
std::list::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 list, 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 elements is allocated using the container's allocator, 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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// list::emplace_front
#include <iostream>
#include <list>
int main ()
{
std::list< std::pair<int,char> > mylist;
mylist.emplace_front(10,'a');
mylist.emplace_front(20,'b');
mylist.emplace_front(30,'c');
std::cout << "mylist contains:";
for (auto& x: mylist)
std::cout << " (" << x.first << "," << x.second << ")";
std::cout << std::endl;
return 0;
}
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Output:
mylist contains: (30,c) (20,b) (10,a)
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Iterator validity
No changes.
Member begin returns a different iterator value.
Data races
The container is modified.
No contained elements are accessed: concurrently accessing or modifying them is safe.
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.