如何从给定指针的向量中删除元素-C ++

Question

If I have a vector that looks like this {a, b, c, d, e, f} and I have a pointer named myPointer and it points to element e , how can I delete e from the vector?

Here is example code of what I would like to do

vector<char> v = {'a', 'b', 'c', 'd', 'e', 'f'};

char *myPointer = &v[4];

// I want to do something like this
v.erase(myPointer);

// Output
// a, b, c, d, f

Can this be done?

Answer 1

You could use a pointer to the first element to calculate the offset, then use that to create an iterator to pass to std::vector::erase .

auto offset = myPointer - v.data();
v.erase(v.begin() + offset);

This assumes myPointer points to an element of v . If not, the behaviour is undefined.

---

Working example:

#include <vector>
#include <iostream>

int main()
{
    std::vector<int> v{1,2,3,4,5,6,7,8};
    int* p = &v[3];

    v.erase(v.begin() + (p - v.data()));

    for (auto i: v)
        std::cout << i << ' ';

    std::cout << '\n';
}

output:

1 2 3 5 6 7 8

Answer 2

The data stored by a vector is contiguous, so you can convert a pointer to an iterator by: getting a pointer to the first element, doing pointer arithmetic to find the difference and then apply that to begin :

assert(v.data() <= mypointer && mypointer < v.data()+v.size());
v.erase(v.begin() + (mypointer - v.data()));