运行.exe文件时出现这个std :: logic错误
basic string::_S_construct null not valid
我搜索了论坛并查看并查看了所有内容，我没有看到我将空引用传递给字符串构造函数的地方，是否有人可以为我发光？
#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;
}
答案 0 :(得分：0)
当您尝试构建_S_construct）string（因此basic_string）将其初始化为NULL（即常量{{}时，会触发此错误1}}）。
在这里，我在代码中可以找到的第一个项目位于(char const *) NULL，您可以将Attendance::Attendance初始化为id（相当于初始化为0）
没有输入错误，因为0是指向常量字符串的指针，但是已经进行了特殊检查以避免在实际尝试读取位置0处的字符串时发生的分段错误。
最有可能的解决方法是将NULL替换为id(0)，并尝试将id("")初始化为std::string（或NULL }）。