Vector push back error - c++

Question

I'm using C++ to implement FP-growth algorithm, but I get some errors when using vector. Here is my code:
typedef struct Node
{
FPData *fpData;
int childCount;
struct Node *parent;
vector<Node*> childs;
}FPNode;
FPNode* FPTree::NewNode(string data, int support)
{
FPNode *node = (FPNode*) malloc(sizeof(FPNode));
FPData *fpData = (FPData*) malloc(sizeof(FPData));
fpData -> data = data;
fpData -> support = support;
node -> fpData = fpData;
node -> childCount = 0;
node -> parent = NULL;
return node;
}
void FPTree::InsertFPPath(FPNode* root, list<FPData*> fpDatas)
{
if(fpDatas.size() <= 0)
{
return;
}
bool flag = true;
for(int i = 0; i < root -> childCount; i++)
{
FPNode* child = root -> childs[i];
if(child -> fpData -> data == fpDatas.front() -> data)
{
flag = false;
child -> fpData -> support ++;
fpDatas.pop_front();
InsertFPPath(child, fpDatas);
break;
}
}
if(flag)
{
FPData* firstData = fpDatas.front();
FPNode* newChild = NewNode(firstData -> data, firstData -> support);
root -> childs.push_back(newChild); // error at here
root -> childCount ++;
fpDatas.pop_front();
for(int i = 0; i < fpDatas.size(); i++)
{
InsertFPPath(newChild, fpDatas);
}
}
}
The InsertFPPath() is a recursive method, I get error when second iterate:
root -> childs.push_back(newChild)
The error comes at:
construct(_Up* __p, _Args&&... __args) // here the __p is null, and __args is right
{
::new((void*)__p) _Up(_VSTD::forward<_Args>(__args)...);
}
And the thread Queue stop at:
#0 0x00000001000050cf in void std::__1::allocator::construct(Node**, Node* const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1673
the backtrace is :
#0 0x00000001000050cf in void std::__1::allocator::construct(Node**, Node* const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1673
#1 0x00000001000050bc in void std::__1::allocator_traits >::__construct(std::__1::integral_constant, std::__1::allocator&, Node**, Node* const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1600
#2 0x000000010000509c in void std::__1::allocator_traits >::construct(std::__1::allocator&, Node**, Node* const&&&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1453
#3 0x0000000100005079 in std::__1::vector >::push_back(Node* const&) [inlined] at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/vector:1590
#4 0x0000000100004fa9 in FPTree::InsertFPPath(Node*, std::__1::list >) at /Users/dorothy/ME/USTC/作业/数据挖掘/experiment/FPTree/FPTree/FPTree.cpp:129
#5 0x00000001000051b4 in FPTree::InsertFPPath(Node*, std::__1::list >) at /Users/dorothy/ME/USTC/作业/数据挖掘/experiment/FPTree/FPTree/FPTree.cpp:135**

Answer 1

When you allocate memory for structures (struct or class) containing constructors, or for structures containing objects that have constructors, then you can't allocate the memory using malloc. The malloc function only allocates memory, but it doesn't call the constructors, and in your case that means that the childs member object will not be constructed and using the vector will lead to undefined behavior.
When allocating memory dynamically in C++ you need to use the new operator:
FPNode *node = new FPNode;
FPData *fpData = new FPData;