C++ error: The iterator has expired, how to solve it?

In C programming, using an iterator (Iterator) is a common way to traverse the elements of a container. However, when traversing a container, sometimes you encounter the problem that the iterator has expired, causing the program to crash or produce unexpected results.

So, what is the problem that the iterator has expired? Simply put, when we use an iterator to traverse a container, if the container is modified (such as adding or deleting elements, etc.), it may cause the iterator to become invalid, that is, the element pointed to by the iterator no longer exists or the position has been changed. changes, an error will occur if the iterator is used again.

How to solve the problem that the iterator has expired? Here are some common solutions:

1. Use the erase function instead of the remove function

In the operation of using container elements, the remove and erase functions are often used. They can both be used to delete elements in a container. However, the remove function only moves the element to be deleted to the end of the container and does not actually delete the element, while the erase function actually deletes the element from the container. Therefore, if we want to delete elements when traversing the container, it is best to use the erase function so as not to cause the iterator to expire.

2. Use the auto keyword

C 11 introduces the auto keyword, which can automatically deduce the iterator type. When using the auto keyword, the compiler will automatically match the iterator type to ensure that the iterator matches the type of the container, thereby avoiding type mismatch problems.

For example:

vector<int> v = {1,2,3,4,5};
for(auto it = v.begin(); it != v.end(); ++it){
    // ...
}

Using the auto keyword allows the compiler to automatically deduce the type of iterator to ensure that it matches the type of the container.

3. Use the correct iterator when modifying the container

When we modify the container, we need to make sure to use the correct iterator. For example, when traversing a vector container, if you want to delete an element, you need to use the erase function, but using the erase function will cause the positions of all elements after the element to change. If we still use the previous iterator to point to the element that has been moved, the iterator will become invalid.

In order to avoid this situation, we can first record the iterator of the position of the element to be deleted, then perform the deletion operation, and update the iterator with the position after the iterator to ensure that the iterator still points correctly s position. The sample code is as follows:

vector<int> v = {1,2,3,4,5};
auto it = v.begin() + 2; // 记录要删除的元素位置
v.erase(it); // 删除元素
it = v.begin() + 2; // 更新迭代器

This ensures that the iterator still points to the correct location and avoids the problem of iterator failure.

In short, when writing C programs, using iterators to traverse a container is a very common operation. However, iterator failure is a very common problem, so we need to pay attention to avoid this problem to ensure the correctness of the program.

The above is the detailed content of C++ error: The iterator has expired, how to solve it?. For more information, please follow other related articles on the PHP Chinese website!