为什么我使用结构体会出错？

我在写通过二叉树前序和中序遍历的结果重构二叉树，但是TreeNode结构体一直报错，不知道哪里出了问题

这是编译器提示的错误信息

这是代码

#include "stdafx.h"
#include <iostream>
#include <vector>
#include <unordered_map>
#include <stdlib.h>

using namespace std;

TreeNode *reConstructBinaryTree(vector<int> pre,vector<int> vin);
TreeNode *buildtreehelper(unordered_map <int,int> &m,vector<int> &pre,int s0,int e0,int s1);

 struct TreeNode {
     int val;
     TreeNode *left;
     TreeNode *right;
     TreeNode (int x) : val(x), left(NULL), right(NULL) {}
  };

int _tmain(int argc, _TCHAR* argv[])
{
    int a[]={1,2,4,5,3,6};
    int b[]={4,2,5,1,3,6};
    vector<int> c(a,a+6);
    vector<int> d(b,b+6);
    unordered_map<int ,int> in;
    unordered_map <int,int> :: iterator p;
    for(int i=0;i<d.size();++i)
    {
       in[d[i]]=i;
    }
    TreeNode *f=reConstructBinaryTree (c,d);
    cout<<f->val <<endl;
    cout<<f->left ->val <<endl;
    cout<<f->right ->val <<endl;
    return 0;
}

TreeNode* reConstructBinaryTree(vector<int> pre,vector<int> vin) {
    unordered_map<int ,int> in;
    unordered_map <int,int> :: iterator p;
    if(pre.empty ())
        return nullptr;
    for(int i=0;i<vin.size();++i)
    {
       in[vin[i]]=i;
    }

    return buildtreehelper (in,pre,0,pre.size()-1,0);
    }

 TreeNode *buildtreehelper(unordered_map <int,int> &m,vector<int> &pre,int s0,int e0,int s1)
{
   if(s0>e0)
       return nullptr ;
   int mid=pre[s1];
   int index=m[mid];
   int leftlen=index-s0-1;
   TreeNode *node=new TreeNode (mid);
   node->left=buildtreehelper (m,pre,s0,index-1,s1+1);
   node->right =buildtreehelper(m,pre,index-1,e0,s0+leftlen+2);
   return node;
}

struct TreeNode要放在

TreeNode *reConstructBinaryTree(vector<int> pre,vector<int> vin);
TreeNode *buildtreehelper(unordered_map <int,int> &m,vector<int> &pre,int s0,int e0,int s1);

上面啊，兄嘚。

改成

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode (int x) : val(x), left(NULL), right(NULL) {}
};

TreeNode *reConstructBinaryTree(vector<int> pre,vector<int> vin);
TreeNode *buildtreehelper(unordered_map <int,int> &m,vector<int> &pre,int s0,int e0,int s1);

将结构体写成

typedef struct TreeNode {
     int val;
     TreeNode *left;
     TreeNode *right;
     TreeNode (int x) : val(x), left(NULL), right(NULL) {}
  }TreeNode;