Cpp std vector erase

std:: vector::erase

Removes from the vector either a single element (position) or a range of elements ([first,last)).

This effectively reduces the container size by the number of elements removed, which are destroyed.

Because vectors use an array as their underlying storage, erasing elements in positions other than the vector end causes the container to relocate all the elements after the segment erased to their new positions. This is generally an inefficient operation compared to the one performed for the same operation by other kinds of sequence containers (such as list or forward_list).

Parameters

position Iterator pointing to a single element to be removed from the vector.
Member types iterator and const_iterator are random access iterator types that point to elements. first, last Iterators specifying a range within the vector] to be removed: [first,last). i.e., the range includes all the elements between first and last, including the element pointed by first but not the one pointed by last.
Member types iterator and const_iterator are random access iterator types that point to elements.

Return value

An iterator pointing to the new location of the element that followed the last element erased by the function call. This is the container end if the operation erased the last element in the sequence.

Member type iterator is a random access iterator type that points to elements.

Example

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// erasing from vector int main () < std::vectorint> myvector; // set some values (from 1 to 10) for (int i=1; i// erase the 6th element myvector.erase (myvector.begin()+5); // erase the first 3 elements: myvector.erase (myvector.begin(),myvector.begin()+3); std::cout "myvector contains:"; for (unsigned i=0; i << myvector[i]; std::cout '\n'; return 0; >

myvector contains: 4 5 7 8 9 10 

Complexity

Linear on the number of elements erased (destructions) plus the number of elements after the last element deleted (moving).

Iterator validity

Iterators, pointers and references pointing to position (or first) and beyond are invalidated, with all iterators, pointers and references to elements before position (or first) are guaranteed to keep referring to the same elements they were referring to before the call.

Data races

The container is modified.
None of the elements before position (or first) is accessed, and concurrently accessing or modifying them is safe.

Exception safety

If the removed elements include the last element in the container, no exceptions are thrown (no-throw guarantee).
Otherwise, the container is guaranteed to end in a valid state (basic guarantee).
An invalid position or range causes undefined behavior.

See also

vector::pop_back Delete last element (public member function) vector::insert Insert elements (public member function)

Источник

std::vector:: erase

Invalidates iterators and references at or after the point of the erase, including the end() iterator.

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos .

The iterator first does not need to be dereferenceable if first == last : erasing an empty range is a no-op.

Contents

[edit] Parameters

[edit] Return value

Iterator following the last removed element.

[edit] Exceptions

Does not throw unless an exception is thrown by the assignment operator of T .

[edit] Complexity

Linear: the number of calls to the destructor of T is the same as the number of elements erased, the assignment operator of T is called the number of times equal to the number of elements in the vector after the erased elements

[edit] Notes

When container elements need to be erased based on a predicate, rather than iterating the container and calling unary erase , the iterator range overload is generally used with std::remove()/std::remove_if() to minimise the number of moves of the remaining (non-removed) elements, this is the erase-remove idiom. std::erase_if() replaces the erase-remove idiom. (since C++20)

[edit] Example

#include #include void print_container(const std::vectorint>& c) { for (int i : c) std::cout   <" "; std::cout  <'\n'; } int main( ) { std::vectorint> c{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; print_container(c); c.erase(c.begin()); print_container(c); c.erase(c.begin() + 2, c.begin() + 5); print_container(c); // Erase all even numbers for (std::vectorint>::iterator it = c.begin(); it != c.end();) { if (*it % 2 == 0) it = c.erase(it); else ++it; } print_container(c); }

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