Question

我用这种方式定义了一个名为nth_best_parse的类：

class nth_best_parse {
      public:
        int traversal;
        int nth_best_active;
        int nth_best_passive;
        double viterbi_prob;

        nth_best_parse();
        nth_best_parse(int t, int nbl, int nbr, double v) {traversal = t; nth_best_active = nbl; nth_best_passive = nbr; viterbi_prob = v;}
    };

然后我将这个nth_best_parse的向量声明为两个不同类的成员：

class Edge {        // an edge associates an Earley style dotted-item with a span
      public:

        <some irrelevant stuff>

        Span span;      // Span of the edge
        bool isActive;
        vector<Traversal *> leading_traversals; // The list of traversals which lead to parsing of this edge

        vector<nth_best_parse> n_best_parses;


        union {
                DottedRule rule_state;  // Accessed if isActive is true
                int symbol;     // Accessed if isActive is false
                                // A symbol corresponding to the category of a passive edge
                                // Put inside this union to save space
        };

        inline int span_length() {return span.end - span.start;}

    };

<some other stuff>

class BPCFGParser {

  public:

    // Some data structures used in intermediary computations for calculating the n-best parses

//    vector<vector<int> > nth_best_pairs;
    vector<vector<nth_best_parse> > n_best_pairs_for_traversals;

    <some other stuff>

    void compute_n_best_parses(Edge *e, int n);

    <some other stuff>
}

然后我用gdb运行这个程序（顺便说一下，我使用Linux Ubuntu 9.04，g ++ 4.3.3，GNU gdb 6.8-debian）并在compute_n_best_parses（）定义的末尾设置一个断点条件（找到我想要的这个函数的确切调用，我是从一个分段错误追溯）。当gdb命中断点时，我发出了一组命令，gdb输出如下：

(gdb) print e->n_best_parses.size()
$27 = 1
(gdb) print e->n_best_parses[0]
$28 = (nth_best_parse &) @0x1e96240: {traversal = 0, nth_best_active = 0, nth_best_passive = 0, viterbi_prob = 0.16666666666666666}
(gdb) print e->n_best_parses[0].traversal
$29 = 0
(gdb) print &(e->n_best_parses[0].traversal)
$30 = (int *) 0x1e96240
(gdb) awatch *$30
Hardware access (read/write) watchpoint 6: *$30
(gdb) print e->n_best_parses
$31 = {<std::_Vector_base<nth_best_parse, std::allocator<nth_best_parse> >> = {
    _M_impl = {<std::allocator<nth_best_parse>> = {<__gnu_cxx::new_allocator<nth_best_parse>> = {<No data fields>}, <No data fields>}, 
      _M_start = 0x1e96240, _M_finish = 0x1e96258, _M_end_of_storage = 0x1e96288}}, <No data fields>}
(gdb) continue
Continuing.
Hardware access (read/write) watchpoint 6: *$30

Old value = 0
New value = 1
0x0000000000408a4c in __gnu_cxx::new_allocator<nth_best_parse>::construct<nth_best_parse> (this=0x1e96208, __p=0x1e96240, __args#0=@0x7fff8ad82260)
    at /usr/include/c++/4.3/ext/new_allocator.h:114
114     { ::new((void *)__p) _Tp(std::forward<_Args>(__args)...); }
(gdb) backtrace
#0  0x0000000000408a4c in __gnu_cxx::new_allocator<nth_best_parse>::construct<nth_best_parse> (this=0x1e96208, __p=0x1e96240, __args#0=@0x7fff8ad82260)
    at /usr/include/c++/4.3/ext/new_allocator.h:114
#1  0x000000000042169c in std::vector<nth_best_parse, std::allocator<nth_best_parse> >::push_back<nth_best_parse> (this=0x1e96208, __args#0=@0x7fff8ad82260)
    at /usr/include/c++/4.3/bits/stl_vector.h:703
#2  0x0000000000402bef in BPCFGParser::compute_n_best_parses (this=0x7fff8ad82770, e=0x7f5492858b78, n=3) at BPCFGParser.cpp:639
#3  0x00000000004027fd in BPCFGParser::compute_n_best_parses (this=0x7fff8ad82770, e=0x7f5492859d58, n=3) at BPCFGParser.cpp:606
#4  0x00000000004027fd in BPCFGParser::compute_n_best_parses (this=0x7fff8ad82770, e=0x7f549285a1d0, n=3) at BPCFGParser.cpp:606
#5  0x00000000004064d8 in main () at experiments.cpp:75

BPCFGParser.cpp的第639行是这样的：

PUSH_BEST_PAIR_FOR_TRAVERSAL(i,row,column,grammar->probs[temp_rule.symbol][temp_rule.expansion]);

这是在文件开头定义的宏：

#define PUSH_BEST_PAIR_FOR_TRAVERSAL(x,y,z,t) n_best_pairs_for_traversals[x].push_back(nth_best_parse(x, y, z, e->leading_traversals[x]->active_edge->n_best_parses[y].viterbi_prob * e->leading_traversals[x]->passive_edge->n_best_parses[z].viterbi_prob * t))

顺便说一句，Traversal类被定义为：

class Traversal {   // Class for a traversal
      public:
        Edge *active_edge;
        Edge *passive_edge;
        Traversal();
        Traversal(Edge *a, Edge *p) {active_edge = a; passive_edge = p;}
    };

所以实际上我正在向向量n_best_pairs_for_traversals推送一些东西，它是BPCFGParser类的一个实例的成员，push_back（）代码以某种方式覆盖了向量n_best_parses，它是类Edge的一个实例的成员。这怎么可能呢？

Answer 1

你显然在某处存在记忆腐败问题但是这里没有足够的信息来帮助你。

但是你正在编写C ++代码，你的类包含指针这不是一个好兆头（在C ++类中几乎不应该有RAW指针）对于没有经验的C ++开发人员来说，这通常也是导致内存损坏的原因！

你是否遵守了4的规则？

确保每个包含RAW拥有指针的类：

构造
复制构造函数
赋值运算符
析构函数。

Answer 2

您确定要将有效的第一个参数传递给宏吗？在执行n_best_pairs_for_traversals[x]时，您可能正在访问界限，因为x大于矢量大小。

Answer 3

我猜你正在使用一个向量来存储对象（可能是Traversal？），没有意识到将新元素推送到该向量上会使指向已经存在于向量中的元素的指针无效。如果是这种情况，请使用deque。

C ++ vector push_back（）会覆盖另一个相同类型的向量？

3 个答案: