基于范围的for循环和std :: vector.push_back（）使程序崩溃 [英] Range-based for loop and std::vector.push_back() crashing the program

问题描述

#include <iostream>
#include <vector>

int main() {
    std::vector<int> vec;
    for (int i = 0; i < 42; ++i) {
        vec.push_back(i);
        vec.push_back(-i);
    }
    for (int x: vec) {
        for (int y: vec) {
            vec.push_back(x + y);
        }
    }
    for (int x: vec) {
        std::cout << x << "\n";
    }
}

是什么导致此代码崩溃？我尝试用-fsanitize = address进行编译，得到 == 9347 == ERROR：AddressSanitizer：地址0x61500000fdb4在pc 0x00010a4f1043 bp上的free-after-free堆使用0x7fff55710b70 sp 0x7fff55710b68 。当我的计算机上x == 0且y == 22时，它在 vec.push_back（x + y）失败。

What's causing this code to crash? I tried compiling it with -fsanitize=address, got ==9347==ERROR: AddressSanitizer: heap-use-after-free on address 0x61500000fdb4 at pc 0x00010a4f1043 bp 0x7fff55710b70 sp 0x7fff55710b68. It fails at vec.push_back(x + y) when x == 0 and y == 22 on my computer.

推荐答案

来自 std :: vector： ：push_back ：

如果新的size（）大于Capacity（），则所有迭代器和引用（包括过去的） -the-end迭代器）无效。否则，只有过去的迭代器才无效。

If the new size() is greater than capacity() then all iterators and references (including the past-the-end iterator) are invalidated. Otherwise only the past-the-end iterator is invalidated.

基于范围的for循环在内部使用迭代器。使用 push_back 可能会使这些迭代器无效。

Range-based for loop uses iterators internally. Using push_back may cause these iterators to be invalidated.

编辑：请注意，当 y == 22 您将第65个元素插入向量中。容量可能为64。许多实现将容量提高2的幂（每次加倍）。

Edit : Notice that when y == 22 you are inserting a 65th element into your vector. It's likely the capacity was 64. Many implementations increase capacity by powers of 2 (doubling it each time).

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