如何解决此分段错误：以下代码的 11 错误？

Posted 2023-02-22

【中文标题】如何解决此分段错误：以下代码的 11 错误？

【英文标题】：How do I solve this segmentation fault : 11 error for the following code?

【发布时间】：2017-12-07 08:49:56

【问题描述】：

这是我尝试使用本地搜索解决 2-SAT 问题的算法。但是，我似乎遇到了分段错误： 11. 问题从for ( int i =0; i<upper_limit; i++) 之后的主代码开始。 如何解决此错误？

#include <fstream>
#include <iostream>
#include<math.h>
#include <map>
#include <vector>
#include <set>
#include <random>
#include <math.h>

using namespace std;

bool check_clause(short &logic,bool x1,bool x2)

    switch(logic)
        
            case 0:
                return ( (not x1) or (not x2) ); 
            case 1:
                return ( (not x1) or x2 );
                break;
            case 2:
                return ( x1 or (not x2) );
                break;
            case 3:
                return( x1 or x2 );
                break;
        
        return false;


int check_logic(vector<int> & elem)

    short logic=0;
    //Creating logic flag to construct teach clause Eg. x or !x2 = (10)(bin)= (2)(decimal)
    for(int j =1; j>=0;j--)
    
        if (elem[j]>0)
        
            logic+=pow(2,1-j);
        
    
    return logic;


vector <int> check_assignment(map <int,bool> &assignment,map <int, vector<int> > &data)
   int count=0;
    vector <int> unsatisfied;
    for (auto elem: data)
       //Variables for both vertex indices for clause and the logic flag
        int first_vertex=abs(elem.second[0]);
        int second_vertex=abs(elem.second[1]);
        short logic=check_logic(elem.second);

        //Retrieving randomly generated boolean variables for first and second vertex of current clause
        bool x1 = assignment[first_vertex];
        bool x2 = assignment[second_vertex];
        bool answer=check_clause(logic,x1,x2);

        if (answer==false)
        
            unsatisfied.push_back(count);
        
        count+=1;

    

    return unsatisfied;


bool isKeyInMap(int number, map <int,vector<int> > & dictionary)

    if (dictionary.find(number)==dictionary.end())
    
        return false;
    
    else
    
        return true;
    


int main()

    random_device rd;
    mt19937 gen(rd());
    uniform_int_distribution<> dis(0,1);
    map <int, vector<int> > data;
    map<int,vector<int> >::iterator it;
    vector<int> row(2,0);   
    ifstream file_read("2sat1.txt");
    int a;
    int n;
    file_read>>n;
    cout<<n<<endl;
    map <int, vector<int> > positives;
    map <int, vector<int> > negatives;
    int count=0;

    while (file_read>>a)
    
        row[0]=a;
        file_read>>a;
        row[1]=a;
        data[count].insert(data[count].end(),row.begin(),row.end());


        for (auto element: row)
        
            if (element<0)
                
                    negatives[ -element ].push_back(count);
                
            else 
            
                positives[ element ].push_back(count);
            


        


        count++;
    


    int n_rows=positives.size();
    int incl_count=0;

    vector <int> deletionList;
    set <int> inclset;
    // cout<<isKeyInMap(200001,positives)<<endl;

    for (int i =1; i<=n;i++)
    
        bool pos_entry=isKeyInMap(i,positives);
        bool neg_entry=isKeyInMap(i,negatives);

        if ( pos_entry != neg_entry )
        
            if (pos_entry==true)
            
                deletionList.insert(deletionList.end(),positives[i].begin(),positives[i].end());
            
            else
            
                deletionList.insert(deletionList.end(),negatives[i].begin(),negatives[i].end());
            
        
        else if ((pos_entry==neg_entry) and (pos_entry==true))
        

            inclset.insert(i);
        


    
    cout<<"Inclusion set size: "<<inclset.size()<<endl;
    int incl_size=inclset.size();

    set <int> deletionSet(deletionList.begin(),deletionList.end());
    cout<<"Set Size: "<<deletionSet.size()<<endl;
    // sort(deletionList.begin(),deletionList.end());

    for (auto i=deletionSet.rbegin(); i!=deletionSet.rend();++i)
    

        for (auto item: data[*i])
        
            cout<<item<<" ";
        
        it=data.find(*i);
        if (it!=data.end())
        
            data.erase(it);
        
        else
        
            cout<<"Not found!"<<endl;
        


    
    cout<<data.size()<<endl;


    map <int,bool> assignment;
    int upper_limit= (int) ceil ( log2(incl_size) );
    long local_iter_size= 2*pow(incl_size,2);

    for (auto elem: inclset)
    
        assignment[elem]=(bool) dis(gen);
    




    for ( int i =0; i<upper_limit; i++)
    

        for (auto elem: inclset)
        
            assignment[elem]= (bool) dis(gen);

        

        for (auto elem: assignment)
        
            cout<<elem.first<<":"<<elem.second<<endl;
        
        cout<<"Size of assignment: "<<assignment.size()<<endl;

        for (int j=0; j<local_iter_size; j++)
        
            cout<<"Okay "<<j<<endl;
            vector <int> unsatisfied;
            unsatisfied = check_assignment(assignment,data);

            if (unsatisfied.empty())
            
                cout<<"Yay, we win!";
                return 0;
            

            int pick_random= unsatisfied[rand()% unsatisfied.size()];
            vector <int> record= data[pick_random];
            short logic=check_logic(record);
            int first_vertex=abs(record[0]);
            int second_vertex=abs(record[1]);
            bool x1=assignment[first_vertex];
            bool x2= assignment[second_vertex];

            if (check_clause(logic,not x1,x2)==true)
            
                assignment[first_vertex]
                = not x1;
            
            else
            
                assignment[second_vertex]=not x2;
            
            cout<<"Number of unfulfilled clauses: "<<unsatisfied.size()<<endl;
        


    

【问题讨论】：

您是否尝试过从代码中剥离内容直到段错误消失？

谢谢。我会试试看。

【参考方案1】：

if (answer==false)
        
            unsatisfied.push_back(count);
        
        count+=1;

在 check_clause 函数中发现的这个子句有错误。我们应该推送不满足子句的键索引，即unsatisfied.push_back(elem.first)。由于这个错误，程序尝试访问向量unsatisfied 范围之外的索引。 现在，代码运行良好。