类声明：链接器命令失败，退出代码为1

Question

我正在尝试在单独的文件中创建BST类，但出现链接器命令失败。我已经检查了很多次，但是找不到错误。这是代码。

BST.h

#ifndef BST_H
#define BST_H
#include <iostream>

using namespace std;

struct node
{
    int data;
    node *left;
    node *right;
};

class BST
{
    private:
    node *root;

    public:
    BST();
    void Insert(int);
    bool Search(int);
    bool Delete(int);
    void Display();
};

#endif

BST.cpp

#include "BST.h"

BST::BST()
{
    root = NULL;
}

void InsertNode(node *&, int);
void BST::Insert(int val)
{
    InsertNode(root, val);
}

bool SearchNode(node *&, int);
bool BST::Search(int val)
{
    return SearchNode(root, val);
}
bool DeleteNode(node *&, int);
bool BST::Delete(int val)
{
    return DeleteNode(root, val);
}

void InOrderTraversalDisplay(node *&);
void BST::Display()
{
    InOrderTraversalDisplay(root);
}

void InsertNode(node *&ptr, int val)
{
    if (ptr == NULL)
    {
        ptr = new node;
        ptr->data = val;
        ptr->left = NULL;
        ptr->right = NULL;
    }

    else if (val > ptr->data)
    {
        InsertNode(ptr->right, val);
    }
    else if (val <= ptr->data)
    {
        InsertNode(ptr->left, val);
    }
}

void InOrderTraversalDisplay(node *&ptr)
{
    if (ptr == NULL)
    {
        cout << "tree is empty" << endl;
    }

    if (ptr->left != NULL)
    {
        InOrderTraversalDisplay(ptr->left);
    }

    cout << ptr->data << endl;

    if (ptr->right != NULL)
    {
        InOrderTraversalDisplay(ptr->right);
    }
}

bool SearchNode(node *&ptr, int val)
{
    if (ptr == NULL)
    {
        return false;
    }
    else if (ptr->data == val)
    {
        return true;
    }
    else
    {
        if (val > ptr->data)
        {
            return SearchNode(ptr->right, val);
        }

        else if (val < ptr->data)
        {
            return SearchNode(ptr->left, val);
        }
    }
    return false;
}

int Getsuccessor(node *ptr)
{
    ptr = ptr->right;
    while (ptr->left != NULL)
    {
        ptr = ptr->left;
    }
    return ptr->data;
}

int Getsuccessor(node *);
bool DeleteNode(node *&ptr, int val)
{
    if (ptr == NULL)
    {
        return false;
    }

    else if (val < ptr->data)
    {
        return DeleteNode(ptr->left, val);
    }

    else if (val > ptr->data)
    {
        return DeleteNode(ptr->right, val);
    }

    else
    {
        if (ptr->left == NULL && ptr->right == NULL)
        {
            delete ptr;
            ptr = NULL;
            return true;
        }

        else if (ptr->left != NULL && ptr->right == NULL)
        {
            node *temp = ptr;
            ptr = ptr->left;
            delete temp;
            return true;
        }

        else if (ptr->left == NULL && ptr->right != NULL)
        {
            node *temp = ptr;
            ptr = ptr->right;
            delete temp;
            return true;
        }
        else
        {
            int succ;
            succ = Getsuccessor(ptr);
            ptr->data = succ;
            return DeleteNode(ptr->right, succ);
        }
    }
}

main.cpp

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

using namespace std;
int main()
{
    BST b;
    b.Insert(5);
    b.Insert(4);
    b.Delete(4);
    b.Delete(14);
    b.Display();

    return 0;
}

出现以下错误。

Undefined symbols for architecture x86_64:
  "BST::Delete(int)", referenced from:
      _main in main-4bcc78.o
  "BST::Insert(int)", referenced from:
      _main in main-4bcc78.o
  "BST::Display()", referenced from:
      _main in main-4bcc78.o
  "BST::BST()", referenced from:
      _main in main-4bcc78.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)