vector iterator not dereferencable怎么处理啊

求解，下面这段代码是可以运行的，不过我把处理的数据换成

 (IP (NP (NP (NP (CP (IP (VP (VV ()(NP (NR 法新社)(NR 伦敦) (NT 一日) (NN 电) (NN )) (NN 火星) (NN 探测)))))(NP (NN 计划)))(NP (NN 发言人)))(NP (NR 巴拉特)))(VP (VV 说) (PU ,)(IP (IP (VP (VV 一枚)(IP (VP (LCP (IP (NP (NP (NR 美国))(NP (NN 卫星)))(VP (ADVP (AD 无法))(PP (P 与)(NP (CP (IP (VP (ADVP (AD 已))(VP (VV 登陆)(NP (NN 火星)))))(DEC 的))(NP (NP (NP (NP (NR 欧洲))(ADJP (JJ 小)) (NP (NN 猎犬)))(QP (OD 二)(CLP (M 号))) (NP (NN ()))(NP (NN BEAGLE))) (NP (QP (CD 2))(NP (NN )))) (NP (NN 登陆艇)))) (ADVP (AD 连)) (VP (VV 系))))(LC 后))(ADVP (AD ,)) (VP (VV 有意)(NP (CP (IP (VP (ADVP (AD 从小))(VP (VV 猎犬)(NP (QP (OD 二)(CLP (M 号)))(NP (NN 搜集)(NN 信号))))))(DEC 的))(NP (NN 希望))))))))(PU ,) (VP (NP (NT 如今))(ADVP (AD 只好)) (VP (VV 寄)(VP (VV 望)(PP (P 于)(NP (NP (PN 它的))(NP (NN 母)(NN 船) (NN 火星)) (ADJP (JJ 特)) (NP (NN 快车))))))) (PU .))))

之后就不能运行了，然后报错说vector iterator not dereferencable

 #include <iostream>
#include <vector>
#include <string>
#include <iterator>
#include <queue>
#include <iomanip>
#include <cstdlib>
using namespace std;

typedef vector<string>::const_iterator iter;

const int word_length = 10;//Max word length, should be even

class SyntaxTree{
    struct Node{
        string tag;
        vector<Node*> children;
        int leaf_num;

        Node(string tag,vector<Node*> children,int leaf_num=0){
            this->tag = tag;
            this->children = children;
            this->leaf_num = leaf_num;
        }
    };

    Node * _root;
public:
    void parseTree(const vector<string>& vec){
        iter be = vec.begin();
        _root = parseTree(be);
    }

    void printTree(){
        queue<Node*> que;
        que.push(_root);
        int level_num = 1;
        bool end_flag = true;
        while(que.size() != 0 && end_flag){
            end_flag = false;
            int new_level_num = 0;
            while(level_num--){
                Node *temp = que.front();
                printAuxi(temp->leaf_num,temp->tag);
                que.pop();
                for(int i=0;i!=temp->children.size();i++){
                    end_flag = true;
                    que.push(temp->children[i]);
                    new_level_num++;
                }
                if(temp->children.size() == 0){
                    que.push(new Node(" ",vector<Node*>(),1));//Empty Node for aligning
                    new_level_num++;
                }
            }
            level_num = new_level_num;
            cout<<endl;
            cout<<endl;
        }
    }
private:
    void printAuxi(int num,string str){
        if(str.size() % 2 == 1)
            str += " ";
        int pad = (word_length * num - str.size()) / 2;
        cout<<setw(pad + str.size())<<str;
        cout<<setw(pad)<<" ";
    }

    Node * parseTree(iter& b){
        if(*b == ")" || *b == "]"){
            b++;
            return NULL;
        } else if( *b == "(" || *b == "["){
            Node *temp = new Node(*(b+1),vector<Node*>());
            b += 2;
            Node *child;
            while((child = parseTree(b)) != NULL){
                temp->children.push_back(child);
                temp->leaf_num += child->leaf_num;
            }
            return temp;
        } else{
            return new Node(*b++,vector<Node*>(),1);
        }

        return NULL;//nosense
    }
};

vector<string> convert(const string& sytree){
    vector<string> ret;
    for(string::const_iterator i = sytree.begin();i != sytree.end();i++){
        if(*i == ' ' | *i == '\t')
            continue;
        else if(*i == '(' || *i == ')' || *i == '[' || *i == ']')
            ret.push_back(string(i,i+1));
        else{
            string::const_iterator j = i+1;
            for (;j != sytree.end() && *j != ' ' && *j != '\t' && *j != '(' && *j != ')' && *j != '[' && *j != ']';j++)
                ;
            ret.push_back(string(i,j));
            i = --j;
        }
    }
    return ret;
}

int main(){
    string test = "(S(NP I)(VP(VP (V shot) (NP (Det an) (N elephant)))(PP (P in) (NP (Det my) (N pajamas)))))";
    vector<string> syt = convert(test);
    SyntaxTree syn;
    syn.parseTree(syt);
    syn.printTree();
    return 0;
}

求帮忙解答一下，我C++几乎是小白啊

vector的迭代器使用有问题，越界了等

在只读迭代器内修改元素或者集合会报这个错误，仔细调试下代码。

就是vector的访问越界了，while(it != '\0')，如果访问数据是字符的话，在访问中加上字符的条件限制试试