好吧，我已经准备好接受教育和侮辱了。我必须制作一个简单的程序，它接受一个字符串并使用链表向后打印它。下面是我的实现，我尝试通过打印第一个节点来测试它，但没有任何显示。为什么会这样？
#include <iostream>
#include <cstddef>
#include <string>
#include <stdio.h>
#include <cstring>
#include <sstream>
using std::cout;
using std::endl;
using std::string;
void addNode(char x);
int main(int argc, const char *argv[]){
string text;
std::cout<<"Insert texst to see it backwards: ";
std::cin >> text;
//convert string to char array
char ctext[1024];
strcpy(ctext, text.c_str());
}
class Node{
friend class LinkedList;
private:
string data;
Node *pnext;
public:
//general constructor
Node(void):pnext(NULL)
{}
//constructor with data value
Node(string val):data(val),pnext(NULL)
{}
//constructor with data and next values
Node(string val, Node* next):data(val), pnext(next)
{}
//Getters
string getValue(void){
return data;
}
Node* getNext(void){
return pnext;
}
};
class LinkedList
{
private:
Node *head;
Node *tail;
public:
LinkedList(void); //general constructor
LinkedList(string val);//constructor with value of a list node
void addNode(char* x);
};
LinkedList::LinkedList(){
head = tail = NULL;
}
LinkedList::LinkedList(string val){
head = new Node(val);
tail = head;
}
void LinkedList::addNode(char* x){
if (head == NULL){
tail = head= new Node(x[0]);
}
else{
int i = 0;
while (x[i]!=NULL){
//creat new node with value
Node* tmp = new Node(x[i]);
//tmp node points to head
tmp->pnext = head;
//tmp becomes new head
head=tmp;
i++;
}
Node *p = head;
std::cout<<p->data;
}
}
除了你从不创建一个列表或在其中放置任何东西......
测试列表中是否没有节点：
if (head == NULL)
这将是真的，因为它是第一次插入。然后创建一个节点：
tail = head= new Node(x[0]);
然后就是这样。您的if块到此结束，并跳到if-else的末尾，那里没有更多的语句，只有函数体的结束大括号。您可能不想使用if-else，而只想使用if。
int i = 0;
if (head == NULL)
{
tail = head= new Node(x[0]);
i = 1;
}
只需确保检查字符串是否超过一个字符即可。
事实上，你需要一个堆栈。可以使用标准容器std::forward_list通过列表以相反的顺序输出字符串。或者当然，您可以使用标准容器适配器std::stack。
如果您需要自己编写列表，则程序可能如下所示
#include <iostream>
#include <string>
class LinkedList
{
private:
struct Node
{
char data;
Node *next;
} *head;
public:
LinkedList() : head( nullptr ) {}
LinkedList( const std::string &s ) : head( nullptr )
{
for ( char c : s ) push_front( c );
}
~LinkedList()
{
while ( head )
{
Node *current = head;
head = head->next;
delete current;
}
}
void push_front( char c )
{
head = new Node { c, head };
}
friend std::ostream & operator <<( std::ostream &, const LinkedList & );
};
std::ostream & operator <<( std::ostream &os, const LinkedList &lst )
{
for ( LinkedList::Node *current = lst.head; current; current = current->next )
{
os << current->data;
}
return os;
}
int main()
{
std::string s( "Hello World!" );
std::cout << s << std::endl;
LinkedList lst( s );
std::cout << lst << std::endl;
return 0;
}
程序输出为
Hello World!
!dlroW olleH
如果需要，可以将自己的方法添加到列表中。例如，您可以添加 clear 或 reset 等方法。
这是添加了方法的同一类 front 和 pop_front .
#include <iostream>
#include <string>
class LinkedList
{
private:
struct Node
{
char data;
Node *next;
} *head;
public:
LinkedList() : head( nullptr ) {}
LinkedList( const std::string &s ) : head( nullptr )
{
for ( char c : s ) push_front( c );
}
~LinkedList()
{
while ( head )
{
Node *current = head;
head = head->next;
delete current;
}
}
LinkedList( const LinkedList & ) = delete;
LinkedList & operator =( const LinkedList & ) = delete;
void push_front( char c )
{
head = new Node { c, head };
}
bool empty() const
{
return head == nullptr;
}
void pop_front()
{
if ( !empty() )
{
Node *current = head;
head = head->next;
delete current;
}
}
char & front()
{
return head->data;
}
const char & front() const
{
return head->data;
}
friend std::ostream & operator <<( std::ostream &, const LinkedList & );
};
std::ostream & operator <<( std::ostream &os, const LinkedList &lst )
{
for ( LinkedList::Node *current = lst.head; current; current = current->next )
{
os << current->data;
}
return os;
}
int main()
{
std::string s( "Hello World!" );
std::cout << s << std::endl;
LinkedList lst( s );
std::cout << lst << std::endl;
while ( !lst.empty() )
{
std::cout << lst.front();
lst.pop_front();
}
std::cout << std::endl;
return 0;
}
程序输出为
Hello World!
!dlroW olleH
!dlroW olleH