c ++向量插入访问冲突读取位置

Question

My vectors are constructed like this:

struct segment {
    float x1;
    float y1;
    float x2;
    float y2;
    float k;
    float b;
};

enum EventType {UPPER_PT = 0, LOWER_PT, INTER_PT};
struct order {
    float x;
    float y;
    vector<segment>::iterator line_id;
    vector<segment>::iterator line2_id;
    EventType type;
};

vector<segment> seg_lines;
vector<order> event_list;

After initializing event_list , I try to insert() a new element at random position like this:

order new_event;
new_event.x = 300;
new_event.y = 400;
new_event.line_id = an_iterator_in_seg_lines;
new_event.line2_id = another_iterator_in_seg_lines;
new_event.type = INTER_PT;

bool inte_inserted = false;
for(vector<order>::iterator tmp_idx = event_list.begin(); tmp_idx != event_list.end(); tmp_idx++) {
    if(a_Y_threshold > tmp_idx->y || a_Y_threshold == tmp_idx->y && an_X_threshold < tmp_idx->x) {
        event_list.insert(tmp_idx, new_event);
        inte_inserted = true;
        break;
    }
}

I can assure you that line_id and line2_id are both valid. I'm just trying to simplify my description.

In this case, it's trying to insert a new_event at the "5th position", while the size and capacity of event_list are both 10 and the event_list is full of valid order .

But I get such error:

Unhandled exception in ... 0xC0000005: Access violation reading location 0x00000000

I think the error code tells me that I'm using an invalid pointer. But I checked my 'Watch' view, and all iterators related (including tmp_idx ) are all valid and pointing to the right positions.

I try to use emplace() instead of insert() , it doesn't work. I tried to resize() my event_list before inserting new element, it doesn't work either. But when I use list to construct event_list instead of vector , it works like a charm.

So, what may have caused this problem and what should I do if I want to stick with vector ?

I'm using VS 2010.

Answer 1

from cplusplus

If a reallocation happens, all iterators, pointers and references related to the container are invalidated.

You are inserting while looping on a vector, which may invalidate your iterators. You could push back elements into the vector instead of inserting them, and only at the end reorder the vector. Much easier and cleaner.