CODEWITHSUNDEEP
c++vectoriteratorlanguage-lawyererase
RiaD
RiaD

Reputation: 47640

Erasing vector::end from vector

Does it works correctly (does nothing) when I use

 vector<T> v;
 v.erase(v.end());

I want to use something like

 v.erase(std::find(...));

Should I if is it v.end() or not?
There is no info about it on C++.com and CPPreference

Upvotes: 50

Views: 27089

Answers (4)

Unmitigated
Unmitigated

Reputation: 89364

Since C++ 17, if statements can have an init statement, so erasing an element that may not be present can be simplified. As a bonus, the variable used for the iterator will not be visible outside the scope of the if statement.

if (auto it = std::find(v.begin(), v.end(), value); it != v.end()) v.erase(it);

In addition, std::ranges::find (or std::ranges::find_if) can be used since C++ 20, which don't require passing in begin() and end() iterators.

if (auto it = std::ranges::find(v, value); it != v.end()) v.erase(it);

The above solutions remove the first occurrence of value if it exists. To remove all occurrences of a value, std::erase from <vector> may be used since C++ 20.

std::erase(v, value);

Upvotes: 0

Gaffi
Gaffi

Reputation: 4367

Have you tried this?

v.erase(remove_if(v.begin(), v.end(), (<your criteria>)), v.end());

Upvotes: 7

Steve Jessop
Steve Jessop

Reputation: 279305

The standard doesn't quite spell it out, but v.erase(q) is defined, "Erases the element pointed to by q" in [sequence.reqmts]. This means that q must actually point to an element, which the end iterator doesn't. Passing in the end iterator is undefined behavior.

Unfortunately, you need to write:

auto it = std::find(...);
if (it != <the part of ... that specifies the end of the range searched>) {
    v.erase(it);
}

Of course, you could define:

template typename<Sequence, Iterator>
Iterator my_erase(Sequence &s, Iterator it) {
    if (it == s.end()) return it;
    return s.erase(it);
}

my_erase(v, std::find(v.begin(), v.end(), whatever));

c.erase() on an associative container returns void, so to generalize this template to all containers you need some -> decltype action.

Upvotes: 45

Billy ONeal
Billy ONeal

Reputation: 106579

Erasing end() (or for that matter, even looking at the target of end()) is undefined behavior. Undefined behavior is allowed to have any behavior, including "just work" on your platform. That doesn't mean that you should be doing it; it's still undefined behavior, and I'll come bite you in the worst ways when you're least expecting it later on.

Depending on what you're doing, you might want to consider set or unordered_set instead of vector here.

Upvotes: 31

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