c++ - 在 C++ 中复制 vector 时 vector 运算符 = 出错

Question

在我的程序中，我正在复制 vector<vector<int> >对另一个这样的:

#include <vector>
#include <cstdlib>
#include <cmath>

typedef std::vector<std::vector<int> > VVector;

VVector mix_genome(VVector mix_genome,
    VVector g1,
    VVector g2,
    int gene_length)
{
    VVector gbuilt = g1; // valgrind gets angry at this a bit...

    for(int i = 0; i < 30; i++)
    {
        int syngamete_chance = std::floor(std::rand() % 100);
        if(syngamete_chance <= 50)
        {
            gbuilt[i] = g2[i];
        }
    }

    int mutation_chance = floor(rand() % 100);

    if(mutation_chance <= 3)
    {
        int gene_num = floor(rand() % 30);
        int act_num = floor(rand() % gene_length+1);
        int rand_act = floor(rand() % 8);

        gbuilt[gene_num][act_num] = rand_act;
    }

    return gbuilt;
}

在运行程序(每隔一段时间调用此函数)大约 3 分钟后，会导致内存访问错误。 Valgrind 为我提供了有关此功能的以下信息:==31557== Invalid write of size 4和 Address 0x10207e360 is 0 bytes after a block of size 16 alloc'd

如果我禁用该函数并且不调用它，程序似乎不会崩溃。 GDB 给我 malloc: *** error for object 0x1068a6878: incorrect checksum for freed object - object was probably modified after being freed. .回溯显示它来自 operator=:

#13 0x000000010000f8d4 in std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > >::operator= (this=0x7fff5fbfe780, __x=@0x7fff5fbfeb50) at vector.tcc:140

我认为这也会导致其他错误，但我不确定。

编辑:

这是我的 Tick()显然也是导致此错误的函数。

int Creature::Tick() {
if(!dead) {
    food--;
    timeLasted++;
    step++;
    if(step > maxStep) {
        step = 0;
    }
    if(cooldown > 0) {
        cooldown--;
    }
    if(xpos > 178) {
        events[EVENT_RIGHT_SEEN_EDGE_OF_SCREEN] = true;
    }
    else if(xpos < 20) {
        events[EVENT_LEFT_SEEN_EDGE_OF_SCREEN] = true;
    }

    if(ypos > 179) {
        events[EVENT_BOTTOM_SEEN_EDGE_OF_SCREEN] = true;
    }
    else if(ypos < 20) {
        events[EVENT_TOP_SEEN_EDGE_OF_SCREEN] = true;
    }
    events[EVENT_NOTHING_HAPPENED] = true;
    for(int z = 0; z < NUM_EVENTS-1; z++) {
        if(events[z]) {
            events[EVENT_NOTHING_HAPPENED] = false; // events[z] is true so something happened
        }
    }
    for(int i = 0; i < NUM_EVENTS-1; i++) { // last event should always be "nothing happened"
        if(events[i]) {
            Action(genome[i][step]); // this has been ided by valgrind: invalid read size 4
            events[i] = false;
        }
    }
    if(!fighting && events[EVENT_NOTHING_HAPPENED]) {
        Action(genome[EVENT_NOTHING_HAPPENED][step]);
    }
    if(food < 0)
        food = 0;
    if(food > maxFood)
        food = maxFood;
    if(food == 0) {
        lifetime -= 5;
    }
    if(xpos > 200-bodySize) {
        xpos = 200-bodySize;
    }
    else if(xpos < 0) {
        xpos = 0;
    }
    if(ypos > 200-bodySize) {
        ypos = 200-bodySize;
    }
    else if(ypos < 0) {
        ypos = 0;
    }
}
return timeLasted;

Answer 1

实际上这个可能是问题所在:

int act_num = floor(rand() % gene_length+1);

你是说

int act_num = rand() % (gene_length+1);

?

这大致符合 valgrind 的最后提示:在 ~(207-188) == ~+19 行无效写入 mix_genome。

这里是相关的部分:

==31557== Invalid write of size 4
==31557==    at 0x100001C43: mix_genome(...) (Game.h:207)

...

==31557==  Address 0x10207e360 is 0 bytes after a block of size 16 alloc'd
==31557==    by 0x10000CB10: std::vector<...>::vector(std::vector<...> const&) (stl_vector.h:233)
==31557==    by 0x100001AD3: mix_genome(std::vector<...>, ...) (Game.h:188)

---

旧答案文本

虽然目前还不知道这是否仍然相关，但最初的分析还展示了如何“读取”valgrind 诊断的其他方法:

您的问题不在于 vector 。看起来您有一个过时的引用(可能是线程错误)。

FPS: 0    # of Creatures: 414    # of Food: 348      ==31557== Invalid read of size 4
==31557==    at 0x1000016BC: Creature::Tick() (Creature.h:204)

这告诉我，在 Tick() 中，您正在更新某种统计数据(包括打印在控制台上的 FPS？)。显然，这是指一个地址:

==31557==  Address 0x100095980 is 0 bytes after a block of size 16 alloc'd
==31557==    at 0xC658: malloc (vg_replace_malloc.c:295)
...
(std::vector<std::vector<int, std::allocator<int> >, std::allocator<std::vector<int, std::allocator<int> > > > const&) (stl_vector.h:233)
==31557==    by 0x10000CCA2: Creature::Creature(Creature const&) (Creature.h:52)

因此，它可能包含对已释放/重新分配的内容的引用。

请注意，当 vector 调整大小时，它们会使所有现有的引用、指针和/或迭代器失效。为了避免这种情况，

• vector::reserve 可用于避免必须根据预期增长进行重新分配
• 你可以使用 vector 索引
• 你可以看看 boost::stable_vector

编辑 事实上，mix_genome 似乎也写入了无效地址。阅读更多您的 valgrind 日志。