使用 valgrind 的地图中的读取大小错误无效

Question

我有这个代码来填充表格，但我不断收到分段错误。我正在尽头试图找到错误可能是什么。我的函数接收 2 个映射并遍历它们以找到公共字符串。它获取这些公共字符串的 int 值并将其放入表中以计算公共字符串的次数。

myMap findTable(mapGraph * dbgraph1, mapGraph * dbgraph2)
{
typedef mapGraph::const_iterator iter;
typedef myMap::const_iterator mapiter;
iter it1 = dbgraph1->begin();
iter it2 = dbgraph2->begin();
int count =0;
myMap * newTable = NULL;
//iterating through the 2 samples of dbgraphs
while (it1 != dbgraph1->end() && it2 != dbgraph2->end())
{
    //a match is found for 2 strings
    if (it1->first == it2->first)
    {
        //the component ids of first sample
        int compdb1 = it1->second->comp;
        //the component ids of second sample
        int compdb2 = it2->second->comp;
        //inserting the component ids and counts in the map
        newTable->insert(make_pair(make_pair(compdb1, compdb2), count));
        count++;
        for (mapiter it = newTable->begin(); it != newTable->end(); it++)
        {
            printf("%i %it %in", it->first.first, it->first.second, it->second);
        }
        it1++;
        it2++;
    }
    //match not found
    else
        it1++;
        it2++;
}
printf("nCLEARn");
return newTable;
}

这是错误：

Address 0x10 is not stack'd, malloc'd or (recently) free'd
Invalid read of size 8
Process terminating with default action of signal 11 (SIGSEGV)
Access not within mapped region at address 0x10

Answer 1

newTable NULL：

myMap * newTable = NULL;

并且从未在以下之前分配给有效对象：

newTable->insert(make_pair(make_pair(compdb1, compdb2), count));

取消引用NULL指针是未定义的行为。为newTable动态分配myMap实例：

myMap* newTable = new myMap(); // Remember to delete later.

或使用堆栈分配的实例：

myMap newTable;

这是一个错误：

//match not found
    else
        it1++;
        it2++;

导致it2在循环的每次迭代中递增，并将导致在end()迭代器上调用++。更改为：

//match not found
    else
    {
        it1++;
        it2++;
    }

或者为了简化代码，只需在循环中的一个位置递增迭代器，因为它们总是递增（在ifelse的每个分支中）。