如何实现链表并允许用户选择要使用 C++ 删除的特定节点?
How can I implement a linked list and allow users to choose a specific node to remove with C++?
我花了几乎一整天的时间试图做到这一点，我理解指针和链表的作用，但我不知道如何实际编码它，我发现的只是Java和C示例，这些示例没有帮助，因为我正在使用C++。 提前感谢您查看我的代码并帮助我，考虑到我花了多少天对此感到压力和困惑，我真的很感激。到目前为止，我不会撒谎，我的大部分 deleteNode 函数可能是垃圾。但就像我说的，我只是迷茫了，我什至不知道从哪里开始或如何进步，因为我只了解这些概念。
这是我的数据文件。
John Doe 80
Jane Smith 70
Bill Jones 50
Pat Hughes 90
Sam Sosa 40
这是我的头文件
#include<string>
using namespace std;
class student {
public:
student(); // constructor method
void st_fn(string fn);
string st_fn();
void st_ln(string ln);
string st_ln();
void st_score(float s);
float st_score();
string st_pass_or_fail();
// need a pointer to the next object
student *nxt_ptr;
protected: // protected can be inherited
float m_score;
string m_ln;
string m_fn;
string m_pf_msg;
};
student::student() //constructor
{
nxt_ptr = NULL;
m_score = 0;
}
void student::st_fn(string fn)
{
m_fn = fn;
}
string student::st_fn()
{
return m_fn;
}
void student::st_ln(string ln)
{
m_ln = ln;
}
string student::st_ln()
{
return m_ln;
}
void student::st_score(float s)
{
m_score = s;
}
float student::st_score()
{
return m_score;
}
string student::st_pass_or_fail()
{
if (m_score >= 60)
m_pf_msg = "PASSED";
else
m_pf_msg = "FAILED";
return m_pf_msg;
}
这是我.cpp文件。
#include<iostream>
#include<string>
#include<fstream>
#include "Header.h"
using namespace std;
int display_menu()
{
int option;
cout << endl << endl;
cout << "1. Display List" << endl;
cout << "2. Add a student" << endl;
cout << "3. Delete first student" << endl;
cout << "4. Search by Last Name" << endl;
cout << "5. Exit" << endl;
cin >> option;
return option;
}
student * search_last_name(student *h)
{
student *f = NULL;
student *t = NULL;
string s_ln;
// prompt for last name to search for
cout << "Enter Last Name of the Student";
cin >> s_ln;
if (h != NULL)
{
t = h;
while (t != NULL)
{
if (t->st_ln() == s_ln)
f = t; // found the last name so save t
t = t->nxt_ptr;
}
}
else
cout << "List is empty" << endl;
return f;
}
void add_student(student *&head) // h is the head of the list
{
student *new_st, *r;
string fn, ln;
float s;
cout << "Enter new students first name, last name and score";
cin >> fn >> ln >> s;
// instantiate a new node, use new_st
new_st = new student;
new_st->st_fn(fn);
new_st->st_ln(ln);
new_st->st_score(s);
if (head == NULL)
head = new_st;
else
{
// find the last node, use r for this
// write code
r = head;
while (r->nxt_ptr != nullptr)
r = r->nxt_ptr;
// add to the back of the list
// write code
r->nxt_ptr = new_st;
} // end of else
} // end of add student
student * delete_front(student * head)
{
student *t;
// delete front node
// check for empty list
if (head != NULL)
{
// delete first node
t = head;
head = head->nxt_ptr;
delete(t);
}
else
cout << "List is empty - nothing to delete" << endl;
return head;
}
void deleteNode(struct Node *head, struct Node *n)
{
// When node to be deleted is head node
if (head == n)
{
n = head->next;
//Remove the link of next node
head->next = head->next->next;
return;
}
//When not first node, folow the normal deletion process
//Find the previous node
struct Node *prev = head;
while (prev->next != NULL && prev->next != n)
prev = prev->next;
// Check if node really exists in Linked List
if (prev->next == NULL)
{
cout << endl << "Given node is not present in Linked List";
return;
}
//Remove node from linked list should it exist
prev->next = prev->next->next;
return;
}
void display_list(student *t)
{
if (t == NULL)
cout << "List is Empty!";
else
{
while (t != NULL)
{
cout << "******Student******" << endl;
cout << t->st_ln() << endl;
cout << t->st_fn() << endl;
cout << t->st_score() << endl << endl;
t = t->nxt_ptr;
}
}
}
int main()
{
string ln, fn;
float s;
int n;
ifstream infile;
student *head = NULL; //pointer to a student object
student *cp = NULL; // pointer to end of the list
student *new_st = NULL; // pointer to a new student object
student *f = NULL; // pointer to found node
int option; // the numbe of menu item the user selects
infile.open("lab8d.txt");
while (!infile.eof())
{
infile >> fn >> ln >> s;
//instantiate a student object
new_st = new student;
//load the object with data
new_st->st_fn(fn);
new_st->st_ln(ln);
new_st->st_score(s);
// check for empty list - its a special case
if (head == NULL)
{
head = new_st;
cp = new_st;
}
else // list is not empty
{
cp->nxt_ptr = new_st;
cp = new_st;
}
} // end of loop
// loop to give the user some options
option = display_menu();
while (option != 5)
{
if (option == 1)
display_list(head);
else if (option == 2)
add_student(head);
else if (option == 3)
head = delete_front(head);
else if (option == 4)
{
f = search_last_name(head);
if (f != NULL)
{
cout << f->st_fn() << endl;
cout << f->st_ln() << endl;
cout << f->st_score() << endl;
cout << f->st_pass_or_fail() << endl;
}
else
cout << "Name not in the list" << endl;
}
else if (option == 6)
{
cout << "Enter the number of the node you would like to delete: " << endl;
cin >> n;
}
option = display_menu();
}
system("pause");
return 0;
}
函数越简单且自包含，它们就越容易测试和调试，并且越不容易失败。
尝试更多类似的东西：
学生.h：
#include <string>
class student_list;
class student
{
public:
student();
student(const std::string &fn, const std::string &ln, float s, student *nxt = NULL);
void next(student *s);
student* next() const;
void firstName(const std::string &fn);
std::string firstName() const;
void lastName(const std::string &ln);
std::string lastName() const;
void score(float s);
float score() const;
std::string pass_or_fail() const;
void display(bool showPassOrFail = false) const;
friend class student_list;
protected: // protected can be inherited
student *m_next;
std::string m_fn;
std::string m_ln;
float m_score;
};
学生.cpp：
#include "Student.h"
#include <iostream>
student::student()
: m_next(NULL), m_score(0)
{
}
student::student(const std::string &fn, const std::string &ln, float s, student *nxt)
: m_next(nxt), m_fn(fn), m_ln(ln), m_score(s)
{
}
void student::next(student *s)
{
m_next = s;
}
student* student::next() const
{
return m_next;
}
void student::firstName(const std::string &fn)
{
m_fn = fn;
}
std::string student::firstName() const
{
return m_fn;
}
void student::lastName(const std::string &ln)
{
m_ln = ln;
}
std::string student::lastName() const
{
return m_ln;
}
void student::score(float s)
{
m_score = s;
}
float student::score() const
{
return m_score;
}
std::string student::pass_or_fail() const
{
if (m_score >= 60)
return "PASSED";
else
return "FAILED";
}
void student::display(bool showPassOrFail) const
{
std::cout << lastName() << std::endl;
std::cout << firstName() << std::endl;
std::cout << score() << std::endl;
if (showPassOrFail)
std::cout << pass_or_fail() << std::endl;
}
学生名单.h：
#include <string>
class student;
class student_list
{
public:
student_list();
~student_list();
student* search_last_name(const std::string &ln);
student* insert(const std::string &fn, const std::string &ln, float s, student* after = NULL);
bool remove(int idx);
void display() const;
private:
student *m_head;
};
学生名单.cpp：
student_list::student_list()
: m_head(NULL)
{
}
student_list::~student_list()
{
while (m_head)
remove(0);
}
student* student_list::search_last_name(const std::string &ln)
{
student *t = m_head;
while (t)
{
if (t->lastName() == ln)
break; // found the last name
t = t->next();
}
return t;
}
student* student_list::insert(const std::string &fn, const std::string &ln, float s, student* after)
{
student **r;
if (after)
{
// add to list after the specified node
// get pointer to next node
r = &(after->m_next);
}
else
{
// add to the back of the list
// find pointer to last node
r = &m_head;
while (*r)
r = &((*r)->m_next);
}
// instantiate a new node
student *new_st = new student(fn, ln, s);
if (after)
new_st->next(*r);
// add to list
*r = new_st;
return new_st;
}
bool student_list::remove(int idx)
{
// delete a node at index
// find pointer to node
student **r = &m_head;
while ((*r) && (idx-- > 0))
r = &((*r)->m_next);
if (*r)
{
// delete node
student *t = *r;
*r = t->next();
delete t;
return true;
}
return false;
}
void student_list::display() const
{
student *t = m_head;
if (!t)
std::cout << "List is Empty!" << std::endl;
else
{
do
{
std::cout << "******Student******" << std::endl;
t->display();
t = t->next();
}
while (t);
}
}
主.cpp：
#include "Student.h"
#include "StudentList.h"
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <limits>
#include <cstdlib>
int read_number()
{
int value;
while (!(std::cin >> value))
{
std::cout << "Must be a number, try again: ";
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), 'n');
}
return value;
}
int display_menu()
{
int option;
std::cout << std::endl << std::endl;
std::cout << "1. Display List" << std::endl;
std::cout << "2. Add a student" << std::endl;
std::cout << "3. Delete first student" << std::endl;
std::cout << "4. Search by Last Name" << std::endl;
std::cout << "5. Delete student by index" << std::endl;
std::cout << "6. Exit" << std::endl << std::endl;
std::cout << "Choice: ";
do
{
option = read_number();
if ((option >= 1) && (option <= 6))
break;
std::cout << "Must be 1..6, try again: ";
}
while (true);
return (option != 6) ? option : -1;
}
int main()
{
student_list students;
std::ifstream infile("lab8d.txt");
if (infile.is_open())
{
student *cp = NULL;
std::string ln, fn;
float s;
while (infile >> fn >> ln >> s)
cp = students.insert(fn, ln, s, cp);
infile.close();
}
// loop to give the user some options
int option; // the number of menu item the user selects
while ((option = display_menu()) != -1)
{
switch (option)
{
case 1:
{
students.display();
break;
}
case 2:
{
// prompt for student info
std::string info;
std::cout << "Enter new student's first name, last name, and score: ";
std::string ln, fn;
float s;
if (std::cin >> fn >> ln >> s)
students.insert(fn, ln, s);
break;
}
case 3:
{
if (!students.remove(0))
std::cout << "List is empty" << std::endl;
break;
}
case 4:
{
// prompt for last name to search for
std::string ln;
std::cout << "Enter Last Name of the Student: ";
if (std::cin >> ln)
{
student *f = students.search_last_name(ln);
if (f)
f->display(true);
else
std::cout << "Name not found in List" << std::endl;
}
break;
}
case 5:
{
std::cout << "Enter the index of the Student to Delete: " << std::endl;
int idx = read_number();
if (!students.remove(idx))
std::cout << "Index not found in List" << std::endl;
break;
}
}
}
std::system("pause");
return 0;
}
话虽如此，您确实应该改用std::list容器，例如：
学生.h：
#include <string>
class student_list;
class student
{
public:
student();
student(const std::string &fn, const std::string &ln, float s);
void firstName(const std::string &fn);
std::string firstName() const;
void lastName(const std::string &ln);
std::string lastName() const;
void score(float s);
float score() const;
std::string pass_or_fail() const;
void display(bool showPassOrFail = false) const;
friend class student_list;
protected: // protected can be inherited
std::string m_fn;
std::string m_ln;
float m_score;
};
学生.cpp：
#include "Student.h"
#include <iostream>
student::student()
: m_score(0)
{
}
student::student(const std::string &fn, const std::string &ln, float s)
: m_fn(fn), m_ln(ln), m_score(s)
{
}
void student::firstName(const std::string &fn)
{
m_fn = fn;
}
std::string student::firstName() const
{
return m_fn;
}
void student::lastName(const std::string &ln)
{
m_ln = ln;
}
std::string student::lastName() const
{
return m_ln;
}
void student::score(float s)
{
m_score = s;
}
float student::score() const
{
return m_score;
}
std::string student::pass_or_fail() const
{
if (m_score >= 60)
return "PASSED";
else
return "FAILED";
}
void student::display(bool showPassOrFail) const
{
std::cout << lastName() << std::endl;
std::cout << firstName() << std::endl;
std::cout << score() << std::endl;
if (showPassOrFail)
std::cout << pass_or_fail() << std::endl;
}
主.cpp：
#include "Student.h"
#include <list>
#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
#include <limits>
#include <algorithm>
#include <cstdlib>
int read_number()
{
int value;
while (!(std::cin >> value))
{
std::cout << "Must be a number, try again: ";
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), 'n');
}
return value;
}
int display_menu()
{
int option;
std::cout << std::endl << std::endl;
std::cout << "1. Display List" << std::endl;
std::cout << "2. Add a student" << std::endl;
std::cout << "3. Delete first student" << std::endl;
std::cout << "4. Search by Last Name" << std::endl;
std::cout << "5. Delete student by index" << std::endl;
std::cout << "6. Exit" << std::endl << std::endl;
std::cout << "Choice: ";
do
{
option = read_number();
if ((option >= 1) && (option <= 6))
break;
std::cout << "Must be 1..6, try again: ";
}
while (true);
return (option != 6) ? option : -1;
}
int main()
{
std::list<student> students;
std::ifstream infile("lab8d.txt");
if (infile.is_open())
{
std::string ln, fn;
float s;
while (infile >> fn >> ln >> s)
students.push_back(student(fn, ln, s));
infile.close();
}
// loop to give the user some options
int option; // the number of menu item the user selects
while ((option = display_menu()) != -1)
{
switch (option)
{
case 1:
{
if (students.empty())
std::cout << "List is Empty!" << std::endl;
else
{
for(const auto &s : students)
{
std::cout << "******Student******" << std::endl;
s.display();
}
}
break;
}
case 2:
{
// prompt for student info
std::string info;
std::cout << "Enter new student's first name, last name, and score: ";
std::string ln, fn;
float s;
if (std::cin >> fn >> ln >> s)
students.push_back(student(fn, ln, s));
break;
}
case 3:
{
if (students.empty())
std::cout << "List is empty" << std::endl;
else
students.erase(students.begin());
break;
}
case 4:
{
// prompt for last name to search for
std::string ln;
std::cout << "Enter Last Name of the Student: ";
if (std::cin >> ln)
{
auto f = std::find(students.begin(), students.end(),
[&](const student &s){ return (s.lastName() == ln); }
);
if (f != students.end())
f->display(true);
else
std::cout << "Name not found in List" << std::endl;
}
break;
}
case 5:
{
std::cout << "Enter the index of the Student to Delete: " << std::endl;
int idx = read_number();
if ((idx < 0) || (idx >= students.size()))
std::cout << "Index not found in List" << std::endl;
else
students.erase(std::next(students.begin(), idx));
break;
}
}
}
std::system("pause");
return 0;
}
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