c++ - 非常简单的程序中的 Apple Mach-O Linker (ld) 错误

Question

我正在执行一项作业，以实现对 AVL 树的插入，但我遇到了三个“Apple Mach-O Linker (ld)”错误。我对这些错误的有限理解是，当从未正确包含在项目中的库中引用某些内容时，它们就会出现。这是 Xcode 给我的错误消息:

Ld /Users/gusmurphy/Library/Developer/Xcode/DerivedData/AVLInsertion-eylpvolyxvuwbygcvocqhleyvzcv/Build/Products/Debug/AVLInsertion normal x86_64
cd /Users/gusmurphy/Documents/CMSC270/AVLInsertion
setenv MACOSX_DEPLOYMENT_TARGET 10.6
/Developer/usr/bin/clang++ -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.6.sdk -L/Users/gusmurphy/Library/Developer/Xcode/DerivedData/AVLInsertion-eylpvolyxvuwbygcvocqhleyvzcv/Build/Products/Debug -F/Users/gusmurphy/Library/Developer/Xcode/DerivedData/AVLInsertion-eylpvolyxvuwbygcvocqhleyvzcv/Build/Products/Debug -filelist /Users/gusmurphy/Library/Developer/Xcode/DerivedData/AVLInsertion-eylpvolyxvuwbygcvocqhleyvzcv/Build/Intermediates/AVLInsertion.build/Debug/AVLInsertion.build/Objects-normal/x86_64/AVLInsertion.LinkFileList -mmacosx-version-min=10.6 -o /Users/gusmurphy/Library/Developer/Xcode/DerivedData/AVLInsertion-eylpvolyxvuwbygcvocqhleyvzcv/Build/Products/Debug/AVLInsertion

Undefined symbols for architecture x86_64:
"AVLTree<int>::insert(int const&)", referenced from:
  _main in main.o
"AVLTree<int>::snapShot(std::ostream&, AVLNode<int>*)", referenced from:
  AVLTree<int>::snapShot(std::ostream&) in main.o
"AVLTree<int>::clear(AVLNode<int>*)", referenced from:
  AVLTree<int>::clear() in main.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

这是“main.cpp”:

#include <iostream>
#include "AVLTree.h"
#include <stdio.h>

int main (int argc, const char * argv[])
{
cout << "Enter an integer to be insterted: " << endl;
int i;
AVLTree<int> tree;
while (true) {
    scanf("%d", &i);
    tree.insert(i);
    tree.snapShot(cout);
    }
}

我特别好奇的一件事是为什么其中一个错误与 AVLTree<int>::clear(AVLNode<int>*) 有关，即使它没有在任何地方明确调用(据我所知)。我还将把 AVLTree 的头文件和实现文件放在这里。

这里是“AVLTree.h”:

#include <iostream>

using namespace std;

#ifndef AVL_TREE
#define AVL_TREE

template<class T>
class AVLNode {
public:
    AVLNode() { 
        left = right = 0; 
    }
    AVLNode(const T& el, AVLNode *l = 0, AVLNode *r = 0, int b = 0) {
        key = el; left = l; right = r; balance = b;
    }
    T key;
    AVLNode *left, *right;
    int balance;
};

template<class T>
class AVLTree {
public:
    AVLTree() { 
        root = 0; 
    }
    ~AVLTree() { 
        clear();
    }
    void clear() {
        clear(root); root = 0;
    }
    bool isEmpty() const { 
        return root == 0; 
    }
    void snapShot(ostream& out) {
        out << "TreeForm[";
        snapShot(out,root);
        out << ']' << endl;
    }
    void preorder() { 
        preorder(root);  
    }
    void inorder() { 
        inorder(root); 
    }
    void postorder() { 
        postorder(root); 
    }
    void insert(const T&);
    T* search(const T& el) const { 
        return search(root,el);
    }
protected:
    AVLNode<T>* root;
    void clear(AVLNode<T>*);
    T* search(AVLTree<T>* p, const T& el) const;
    void preorder(AVLNode<T>*);
    void inorder(AVLNode<T>*);
    void postorder(AVLNode<T>*);
    void snapShot(ostream& out,AVLNode<T> *p);
    void visit(AVLNode<T>* p) { 
        cout << p->key << ' '; 
    }
    void rightRotation(AVLNode<T>* &node) {
        AVLNode<T>* left = node->left;

        node->left = left->right;
        left->right = node;
        node = left;
    }
    void leftRotation(AVLNode<T>* &node) {
        AVLNode<T>* right = node->right;

        node->right = right->left;
        right->left = node;
        node = right;
    }
};

#endif

和“AVLTree.cpp”:

#include "AVLTree.h"
#include <iostream>

template<class T>
void AVLTree<T>::clear(AVLNode<T> *p) {
    if (p != 0) {
        clear(p->left);
        clear(p->right);
        delete p;
    }
}

template<class T>
void AVLTree<T>::insert(const T& el) {  
    if (root == 0) {
        root = new AVLNode<T>(el);
        return;
    }

    AVLNode<T>* parent = 0;
    AVLNode<T>** tmp = root;
    AVLNode<T>* ancestor = 0;

    while (tmp != 0) {
        parent = *tmp;
        if (ancestor == 0 && (parent->balance == 1 || parent->balance == -1))
            ancestor = parent;
        // "ancestor" will point to the first node with an unnacceptable balance, if there is one.
        if (el >= parent) {
            tmp = parent->right;
            parent->balance++;
        } else {
            tmp = parent->left;
            parent->balance--;
        }
    };
    tmp = new AVLNode<T>(el);

    if (ancestor != 0) {
        if (ancestor->balance != 0) {
            if (el >= ancestor->key) {
                if (el >= parent) {
                    rightRotation(ancestor);
                } else {
                    rightRotation(parent);
                    rightRotation(ancestor);
                }
            } else {
                if (el < parent) {
                    leftRotation(ancestor);
                } else {
                    leftRotation(parent);
                    leftRotation(ancestor);
                }
            }
        }
    }
}

template<class T>
T* AVLTree<T>::search(AVLTree<T>* p, const T& el) const {
    while (p != 0)
        if (el == p->key)
            return &p->key;
        else if (el < p->key)
            p = p->left;
        else p = p->right;
    return 0;
}

template<class T>
void AVLTree<T>::inorder(AVLNode<T> *p) {
    if (p != 0) {
        inorder(p->left);
        visit(p);
        inorder(p->right);
    }
}

template<class T>
void AVLTree<T>::preorder(AVLNode<T> *p) {
    if (p != 0) {
        visit(p);
        preorder(p->left);
        preorder(p->right);
    }
}

template<class T>
void AVLTree<T>::postorder(AVLNode<T>* p) {
    if (p != 0) {
        postorder(p->left);
        postorder(p->right);
        visit(p);
    }
}

template <class T>
void AVLTree<T>::snapShot(ostream& out, AVLNode<T> *p)
{
    out << '\"' << p->key << '\"';
    if(p->left != 0 || p->right != 0) {
        out << '[';
        if(p->left==0)
            out << "\"\"";
        else
            snapShot(out,p->left);
        out << ',';
        if(p->right==0)
            out << "\"\"";
        else
            snapShot(out,p->right);
        out << ']';
    }
}

非常感谢您的宝贵时间!很抱歉针对此错误消息创建了另一个线程，但我无法从我发现的问题中总结出很多关于我的问题实例。

Answer 1

模板类定义必须在头文件中可用。你可以阅读这个 here .