Why Does Erasing Vector Elements with an Iterator Crash Without a Specific Conditional Check?

Why Does "Vector Erase Iterator" Code Crash Without an Additional Conditional Check?

Consider the following code:

vector<int> res;
res.push_back(1);
vector<int>::iterator it = res.begin();
for( ; it != res.end(); it++)
{
    it = res.erase(it);
}

This code attempts to erase all elements from a vector using an iterator. However, it crashes without the following additional conditional check:

if(it == res.end())
    return 0;

Explanation

The erase function returns an iterator pointing to the next element after the erased element. When the last element is erased, the returned iterator is equal to res.end().

In the original code, without the conditional check, the for loop continues to increment the iterator even after reaching the end of the vector. This results in an attempt to access memory beyond the bounds of the vector, leading to a crash.

By using the conditional check, the loop terminates when the iterator reaches the end of the vector (it == res.end()). This prevents the crash.

Alternative Loop Structure

To avoid the need for the conditional check, you can rewrite the loop as follows:

while (it != res.end())
{
    it = res.erase(it);
}

This loop will automatically terminate when it reaches res.end(), as the condition will no longer hold true.

Additional Considerations

When erasing elements conditionally, it is necessary to increment the iterator manually if the element is not erased. This can be achieved using:

for ( ; it != res.end(); )
{
   if (condition) 
        it = res.erase(it);
   else 
        ++it;
}

The above is the detailed content of Why Does Erasing Vector Elements with an Iterator Crash Without a Specific Conditional Check?. For more information, please follow other related articles on the PHP Chinese website!