c++ - 运行 .exe 文件时出现 std::logic 错误

Question

我在运行 .exe 文件时遇到这个 std::logic 错误

basic string::_S_construct null not valid

我搜索了论坛，到处看了又看，但我没有看到我将空引用传递给字符串构造函数的位置，有人可以为我发光吗？

#include <iostream>
#include <cstdlib>
#include <fstream>
#include <cstring>
using namespace std;

class Attendance        //parent class called Attendance
{
  public:
     Attendance() : name("Not Assigned"), id(0), num_modules(0),num_contact_hours(0), num_attended(0) { }       //default constructor
     //below is a constructor 
     Attendance(string n, string id, int num_mod, int num_hours, int num_att) : name(n), id(id), num_modules(num_mod), num_contact_hours(num_hours), num_attended(num_att) { }
      ~Attendance() { } //destructor

  // you place your other functions here...

  protected:
     string name;       //name of person
     string id;         //staff or studentid
     int num_modules, num_contact_hours, num_attended;  //the array contains the number of hours in the first sem and second sem
};



class Staff : public Attendance     //subclass for Staff attendace
{
public:
   void initialize_staff(string, string, int, int, int, int, int);
   Staff() : lecture_hours(16), type("Full time") { }       //default constructor, default lecturing hours should be 16
   Staff(string n, string id, int mod, int contact, int attend, int hours, string t) : Attendance(n, id, num_modules, num_contact_hours, num_attended), lecture_hours(hours), type(t) { }
   ~Staff() { }     //destructor
   void setLecturingHours(int hours) { lecture_hours = hours; } //member function (mutator) of subclass that sets lecture hours
   int LecturingHours() { return lecture_hours; }       //accessor function that returns the lecturer hours
   void setType(string t) { type = t; }     //mutator function for 
   string Lecturer_Type() { return type; }  
   void initialize_staff(string,string,int,int,int,string);
   void add();
   void display();
   bool find_free_pos();
    friend istream& operator >> (istream& in, Staff& staff_);
    friend ostream& operator << (ostream& out, Staff& staff);
private:
    int lecture_hours;
   string type;  // full time or part-time
};

class Student : public Attendance
{
   public:
    Student() : type("Undefined") {}
    Student(string n, string id, int mod, int attend, int hours, string t) : Attendance(n, id, mod, num_contact_hours, attend), type(t) {}
    ~Student() {};
    void initialize_student(string,string,int,int,int,string);
    void add();
    void display();
    friend istream& operator >> (istream& in, Student& student_);
    friend ostream& operator << (ostream& out, Student& student);
    bool find_free_pos();

    void setContactHours(int hours) {};
    int getContactHours() {return num_contact_hours;};


   private:
    string type;
    // you populate your variables here
};


int main(int argc, char** argv) 
{
    int i=0, choice_task_menu=0, position=0, num_attend=0, num_modules=0, choice_search, num_contact_hours, lecture_hours;      //variables
    string name, id, type;


    Student *student; //declaring pointer called student that will point to object of class Student
    student = new Student[50];  //object created in dynamic memory

    Staff *staff;       //declaring pointer called staff that will point to object of class Staff
    staff = new Staff[50];  //object created in dynamic memory


    Staff staf_count;   //variables just to count the number of rows in file and do nothing else
    Student stud_count; //variables just to count number of rows in file

    ifstream fin1, fin2, fin3, fin4;                // input file stream, fin1 declared
    fin1.open("attendance_student.txt", ios::in);       //open a text file named "student_attendance.txt"
    if(fin1.fail())             //if it fails, output the following and exit the programs
    {
    cout << "Error opening file for reading\n";
    exit(1);
    }

    int count_student = 0, count_staff = 0;             //initialize count to zero
    while(fin1 >> stud_count) // while true (there are values to read in), exucute the loop again           |{line includes call to overloading operators}|
    {                   
        count_student++;                //post-increment the count each time the 6 variables (a row) are filled
    }
    fin1.close();           //close file
    cout << "the number of rows in the students file: " << count_student << endl;


    fin2.open("attendance_staff.txt", ios::in);     //open a text file named "staff_attendance.txt"
    if(fin2.fail())             //if it fails, output the following and exit the programs
    {
    cout << "Error opening file for reading\n";
    exit(1);
    }

    count_staff = 0;                //initialize count to zero
    while(fin2 >> staf_count) // while true (there are values to read in), exucute the loop again           |{line includes call to overloading operators}|
    {                   
        count_staff++;              //post-increment the count each time the 6 variables (a row) are filled
    }
    fin2.close();           //close file
    cout << "the number of rows in the staff file: " << count_staff << endl;

    fin3.open("attendance_student.txt", ios::in);       //opens file named "phonebook.txt"
    if(fin1.fail())         //if it fails to open file, display the following and exits program
    {
    cout << "Error opening file for reading\n";
    exit(1);
    }

    i = 0;              //read the contents in to myphbk now
    while(fin3 >> student[i] && i < count_student)
    {   
    i++;    
    }

    for(i=0;i<50;i++)       //displays every student
    student[i].display();

    //now it will operate the staff

    fin4.open("attendance_staff.txt", ios::in);     //opens file named "phonebook.txt"
    if(fin4.fail())         //if it fails to open file, display the following and exits program
    {
    cout << "Error opening file for reading\n";
    exit(1);
    }

    i = 0;              //read the contents in to myphbk now
    while(fin4 >> staff[i] && i < count_staff)
    {   
    i++;    
    }

    for(i=0;i<50;i++)       //displays every contact
    staff[i].display();


    //overloading operators later 




    int pos = 0;
    for(pos = 0; pos < 50; pos++)           // initializing everything to undefined, and position to free (position is the second parameter sended in)  
    {
        //the sequence goes like this (name,id,num_modules,num_contact_hours,num_attend,type)
        student[pos].initialize_student( "Undefined", "0", 0, 0, 0,"Undefined");    //initialize everything to zero and strings are undefined
        staff[pos].initialize_staff("Undefined", "0",0 ,0,0, "Undefined");
        //void Student::initialise(string name_,string id_, int num_modules_, int num_contact_hours_, int num_attended_, int type_)
        //void Staff::initialise(string name_, string id_, int num_modules_, int lecture_hours_, int num_attended_, string type_)
        //take previous two comments away

    }

    cout << "Please select option (1. Add a person/2. Search for a person)" << endl;
    cin >> choice_task_menu;    //menu only gives 2 choices (add or search for an individual)

    switch(choice_task_menu)
    {
        case(1):    // add a person, now its classified staff or student
            cout << "Please enter the position of the person (1. Staff/ 2. Student)" << endl;
            cin >> position;



            //if 1, call staff initialize function, if 2, call student initialize function
            if(position == 1)
            {
                for(int i=0;i<100;i++)
                {   
                    if(student[i].find_free_pos())
                    {
                        student[i].add();
                    }
                }
            }
            break;

            if(position == 2)
            {
                for(int i=0; i<100; i++)
                {
                    if(student[i].find_free_pos())
                    {
                        student[i].add();
                    }
                }
            }
        case(2):
            cout << "How do you want to search (1. Name/2. ID)" << endl;
            cin >> choice_search;
    }

    return 0;
}

void Student::initialize_student(string name_,string id_, int num_modules_, int num_contact_hours_, int num_attended_, string type_)
{
    //now assign them to private member variables
    name = name_;
    id = id_;
    num_modules = num_modules_;
    num_contact_hours = num_contact_hours_;
    type = type_;
    num_attended = num_attended_;


    //end of assigning
}

void Staff::initialize_staff(string name_, string id_, int num_modules_, int lecture_hours_, int num_attended_, string type_)
{
    //assigning to private member variables
    name = name_;
    id = id_;
    num_modules = num_modules_;
    type = type_;
    num_attended = num_attended_;
    lecture_hours = lecture_hours_;

}

bool Student::find_free_pos()
{
    if (name == "Undefined")
    {
        return true;
    }
}

bool Staff::find_free_pos()
{
    if (name == "Undefined")
    {
        return true;
    }
}

void Student::add()
{
            cout << "Please enter the type of the person (Full time/Part Time)" << endl;
            cin >> type;
            cout << "Please enter name of person you wish to add" << endl;
            cin >> name;
            cout << "Please enter the ID of the person" << endl;
            cin >> id;      //remember that id is type string
            cout << "Please enter number of contact hours" << endl;
            cin >> num_contact_hours;
            cout << "Please enter number of hours that the person attended" << endl;
            cin >> num_attended;
            cout << "Please enter the number of modules that the person has" << endl;
            cin >> num_modules;
}

void Staff::add()
{
            cout << "Please enter the type of the person (Full time/Part Time)" << endl;
            cin >> type;
            cout << "Please enter name of person you wish to add" << endl;
            cin >> name;
            cout << "Please enter the ID of the person" << endl;
            cin >> id;      //remember that id is type string
            cout << "Please enter number of hours that the person attended" << endl;
            cin >> num_attended;
            cout << "Please enter the number of modules that the person has" << endl;
            cin >> num_modules;
            cout << "Please enter lecture hours (if any)" << endl;
            cin >> lecture_hours;
}

void Student::display()
{
    cout << name << " " << type << " " << id << " " << num_contact_hours << " " <<  num_modules << " " << num_attended;
}

void Staff::display()
{
    cout << name << " " << type << " " << id << " " << lecture_hours << " " <<  num_modules << " " << num_attended;
}

istream& operator >> (istream& in , Staff& staff)       //overloading operator on insertion operator
{
    in >> staff.name >> staff.type >> staff.id >> staff.lecture_hours >> staff.num_modules >> staff.num_attended;
    return in;
}

ostream& operator << (ostream& out , Staff& staff)      //overloading operator on extraction operator
{
    out << staff.name << staff.type << staff.id << staff.lecture_hours << staff.num_modules << staff.num_attended;
    return out;
} 

istream& operator >> (istream& in , Student& student)       //overloading operator on insertion operator
{
    in >> student.name >> student.type >> student.id >> student.num_contact_hours >> student.num_modules >> student.num_attended;
    return in;
}

ostream& operator << (ostream& out , Student& student)      //overloading operator on extraction operator
{
    out << student.name << student.type << student.id << student.num_contact_hours << student.num_modules << student.num_attended;
    return out;
} 

Answer 1

当您尝试构造(因此 _S_construct)string(因此 basic_string)并将其初始化为 时，会触发此错误NULL(即常量 (char const *) NULL)。

在这里，我在您的代码中找到的第一个项目是 Attendance::Attendance，您将 id 初始化为 0(这相当于初始化为 NULL)。

没有打字错误，因为 0 是指向常量字符串的指针，但已进行特殊检查以避免在实际尝试读取位置 0 处的字符串时发生段错误。

最有可能的解决办法是用 id("") 替换 id(0)，在任何你尝试初始化 std 的地方都是一样的::string 到 NULL(或 0)。