Is it Safe to Call `erase()` on a C Map Element During Iteration?

Consequences of Calling erase() on a Map Element During Iteration from Beginning to End

When iterating through a map in C , it is essential to consider the implications of calling the erase() method on a map element within the loop. Specifically, the question arises: is it safe to erase the element and continue iterating, or is it necessary to collect the keys in another container and perform a separate loop for erasure?

In C 03, erasing elements from a map does not invalidate any iterators except those pointing to the element that was deleted. However, it's crucial to note that your code is modifying the iterator after calling erase. This is problematic because pm_it becomes invalid once erase is called. To address this, you should increment the iterator before calling erase.

map<string, SerialdMsg::SerialFunction_t>::iterator pm_it = port_map.begin();
while (pm_it != port_map.end()) {
    if (pm_it->second == delete_this_id) {
        port_map.erase(pm_it++);  // Use iterator and post-increment
    } else {
        ++pm_it;  // Can use pre-increment here for efficiency
    }
}

In C 11, a significant improvement was made to erase, as it now returns the next iterator. This eliminates the need for the awkward post-increment technique shown above. Instead, you can write:

auto pm_it = port_map.begin();
while (pm_it != port_map.end()) {
    if (pm_it->second == delete_this_id) {
        pm_it = port_map.erase(pm_it);
    } else {
        ++pm_it;
    }
}

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