错误：SList.cpp：(.text+0x69)：尝试将节点插入链表头C++时未定义对"SLNode：：SLNode()"的引用

Question

我正试图将一个节点插入到我创建的链表的头部，但在尝试编译时一直出现错误。该错误表明，我在SList类的insertHead函数中有一个未定义的引用，指向我试图调用的函数。

SList.cpp：

/*
 * SList.cpp
 *
 * written by Carlos D. Escobedo
 * created on 26 Oct
 *
 * References:
 */
#include "SList.h"
SList::SList() {
    head = NULL;
    size = 0;
}
SList::~SList() {
    SList::clear();
}
void SList::insertHead(int value) {
    if (head == NULL) {
        head = new SLNode();
    } else {
    }
}
void SList::removeHead() {
    if (head != NULL)
        head = NULL;            
}
void SList::clear() {
    head = NULL;
}
unsigned int SList::getSize() const {
    return size;
}
string SList::toString() const {
    stringstream ss;
    /*
    if (head == NULL) {
        return "";    
    } else {
        for (int i = 0; i < (size-1); i++) {
           ss << head[i] << ", "; 
        }
        ss << head[size-1];
    }
    */
    return "hello";
}

SList.h：

/*
 * SList.cpp
 *
 * written by Carlos D. Escobedo
 * created on 26 Oct
 *
 * References:
 */
#ifndef SLIST_H
#define SLIST_H
#include "SLNode.h"
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
class SLNode;
class SList {
public:
    SList();
    ~SList();
    void insertHead(int value);
    void removeHead();
    void clear();
    unsigned int getSize() const;
    string toString() const;
private:
    SLNode* head;
    unsigned int size;
};
#endif

SLNode.cpp:

/*
 * SLNode.cpp
 * 
 * written by Carlos D. Escobedo
 * created on 20 oct
 * 
 * References: 
 */
#include "SLNode.h"

SLNode::SLNode() {
    nextNode = NULL;
    contents = 0;
}
SLNode::SLNode(int value) {
    nextNode = NULL;
    contents = value;
}
SLNode::~SLNode() {
    nextNode = NULL;
}
void SLNode::setContents(int newContent) {
    contents = newContent;
}
int SLNode::getContents() const {
    return contents;
}
void SLNode::setNextNode(SLNode* newNode) {
    nextNode = newNode;
}
SLNode* SLNode::getNextNode() const {
    return nextNode;
}

SLNode.h：

/*
 * SLNode.cpp
 * 
 * written by Carlos D. Escobedo
 * created on 20 oct
 * 
 * References: 
 */
#ifndef SLNODE_H
#define SLNODE_H
class SList;
class SLNode {
public:
    SLNode();
    SLNode(int contents);
    ~SLNode();
    void setContents(int newContent);
    int getContents() const;
    void setNextNode(SLNode* newNode);
    SLNode* getNextNode() const;
private:
    SLNode* nextNode;
    int contents;
};
#endif

Makefile:

# Target for programming challenge-18
# Date completed: 10-26-2015
pc18: pc18.cpp SList.cpp SList.h SLNode.cpp SLNode.h
    g++ -o challenge-18 pc18.cpp SList.cpp SLNode.h

Answer 1

由于SLNode仅在SList.cpp中使用，我猜您的编译命令不会编译SLNode.cpp