Difference between revisions of "cpp/container/vector/erase"
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{{cpp/container/erase|vector}} | {{cpp/container/erase|vector}} | ||
| + | |||
| + | Example | ||
| + | |||
| + | <code>//erasing from vector | ||
| + | #include <iostream> | ||
| + | #include <vector> | ||
| + | using namespace std; | ||
| + | int main () | ||
| + | { | ||
| + | unsigned int i; | ||
| + | vector<unsigned int> myvector; | ||
| + | // set some values (from 1 to 10) | ||
| + | for (i=1; i<=10; i++) myvector.push_back(i); | ||
| + | // erase the 6th element | ||
| + | myvector.erase (myvector.begin()+5); | ||
| + | // erase the first 3 elements: | ||
| + | myvector.erase (myvector.begin(),myvector.begin()+3); | ||
| + | cout << "myvector contains:"; | ||
| + | for (i=0; i<myvector.size(); i++) | ||
| + | cout << " " << myvector[i]; | ||
| + | cout << endl; | ||
| + | return 0; | ||
| + | }</code> | ||
| + | |||
| + | [http://www.cplusplus.com/reference/stl/vector/erase/] | ||
Revision as of 00:34, 15 October 2011
| (1) | ||
iterator erase( iterator pos ); |
(until C++11) | |
| iterator erase( const_iterator pos ); |
(since C++11) (constexpr since C++20) |
|
| (2) | ||
iterator erase( iterator first, iterator last ); |
(until C++11) | |
| iterator erase( const_iterator first, const_iterator last ); |
(since C++11) (constexpr since C++20) |
|
Erases the specified elements from the container.
[first, last).Iterators (including the end() iterator) and references to the elements at or after the point of the erase are invalidated.
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 |
Parameters
| pos | - | iterator to the element to remove |
| first, last | - | range of elements to remove |
| Type requirements | ||
-T must meet the requirements of MoveAssignable.
| ||
Return value
Iterator following the last removed element.
[first, last) is an empty range, then last is returned.Exceptions
Does not throw unless an exception is thrown by the assignment operator of T.
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.
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)
Example
#include <vector> #include <iostream> void print_container(const std::vector<int>& c) { for (int i : c) std::cout << i << ' '; std::cout << '\n'; } int main() { std::vector<int> 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::vector<int>::iterator it = c.begin(); it != c.end();) { if (*it % 2 == 0) it = c.erase(it); else ++it; } print_container(c); }
Output:
0 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 6 7 8 9 1 7 9
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 151 | C++98 | first was required to be dereferenceable, which made the behavior of clearing an empty vector undefined
|
not required if first == last |
| LWG 414 | C++98 | iterators at the point of erase were not invalidated | they are also invalidated |
See also
| erases all elements satisfying specific criteria (function template) | |
| clears the contents (public member function) |
Example
//erasing from vector
- include <iostream>
- include <vector>
using namespace std; int main () {
unsigned int i; vector<unsigned int> myvector; // set some values (from 1 to 10) for (i=1; i<=10; i++) myvector.push_back(i); // erase the 6th element myvector.erase (myvector.begin()+5); // erase the first 3 elements: myvector.erase (myvector.begin(),myvector.begin()+3); cout << "myvector contains:"; for (i=0; i<myvector.size(); i++) cout << " " << myvector[i]; cout << endl; return 0;
}
