我正在制作Avl树项目，但遇到2个构建错误，即
error LNK1169: one or more multiply defined symbols found
error LNK2005: "struct avl_node * root" (?root@@3PAUavl_node@@A) already defined in AVL.obj
这是我的代码：
#include "AVL.h"
int main()
{
AVL obj;
char pn[30],fn[30],add[20],di[15],dn[30];
int id,age,nic;
int ch;
cout<<"Want To Build BST On Basis Of:"<<endl
<<"1.NIC"<<endl
<<"2.ID"<<endl;
cout<<"Enter Your Choice:";
cin>>ch;
switch(ch)
{
case 1:
do{
cout<<"Patients Database"<<endl
<<"1.Enter New Record"<<endl
<<"2.Search Record"<<endl
<<"3.Delete Record"<<endl
<<"4.Show Record"<<endl
<<"5.Exit"<<endl;
cout<<"What Do You Want To Do:";
cin>>ch;
switch(ch)
{
case 1: cout<<"Enter Patient ID:";
cin>>id;
cin.clear();
cin.ignore();
cout<<"Enter Patient Name:";
gets(pn);
cout<<"Enter Father Name:";
gets(fn);
cout<<"Enter Patient's Age:";
cin>>age;
cout<<"Enter Patient NIC:";
cin>>nic;
cin.clear();
cin.ignore();
cout<<"Enter Address:";
gets(add);
cout<<"Enter Disease:";
gets(di);
cout<<"Enter Doctor Name:";
gets(dn);
root=obj.adddatanic(root,id,pn,fn,age,nic,add,di,dn);
break;
case 2: obj.searchbynic();
break;
case 3:
break;
case 4: cout<<"Show Record:-"<<endl
<<"1.Show Greatest NIC"<<endl
<<"2.Show Least NIC"<<endl
<<"3.Show All Records In Ascending Order"<<endl
<<"4.Show All Records In Descending Order"<<endl;
cout<<"Enter Your Choice:";
cin>>ch;
switch(ch)
{
case 1: obj.showgreatestnic();
break;
case 2: obj.showleastnic();
break;
case 3: obj.showascendingnic();
break;
case 4: obj.showdescendingnic();
break;
}
break;
case 5: exit(-1);
default: cout<<"Wrong Entry"<<endl;
break;
}
}
while(ch!=5);
break;
case 2:
do{
cout<<"Patients Database"<<endl
<<"1.Enter New Record"<<endl
<<"2.Search Record"<<endl
<<"3.Delete Record"<<endl
<<"4.Show Record"<<endl
<<"5.Exit"<<endl;
cout<<"What Do You Want To Do:";
cin>>ch;
switch(ch)
{
case 1: cout<<"Enter Patient ID:";
cin>>id;
cin.clear();
cin.ignore();
cout<<"Enter Patient Name:";
gets(pn);
cout<<"Enter Father Name:";
gets(fn);
cout<<"Enter Patient's Age:";
cin>>age;
cout<<"Enter Patient NIC:";
cin>>nic;
cin.clear();
cin.ignore();
cout<<"Enter Address:";
gets(add);
cout<<"Enter Disease:";
gets(di);
cout<<"Enter Doctor Name:";
gets(dn);
root=obj.adddataid(root,id,pn,fn,age,nic,add,di,dn);
break;
case 2: obj.searchbyid();
break;
case 3:
break;
case 4: cout<<"Show Record:-"<<endl
<<"1.Show Greatest ID"<<endl
<<"2.Show Least ID"<<endl
<<"3.Show All Records In Ascending Order"<<endl
<<"4.Show All Records In Descending Order"<<endl;
cout<<"Enter Your Choice:";
cin>>ch;
switch(ch)
{
case 1: obj.showgreatestid();
break;
case 2: obj.showleastid();
break;
case 3: obj.showascendingid();
break;
case 4: obj.showdescendingid();
break;
}
break;
case 5: exit(-1);
default: cout<<"Wrong Entry"<<endl;
break;
}
}
while(ch!=5);
break;
}
return 0;
}
这是我的AVL.h文件。
#include <iostream>
#include <string>
#include <fstream>
#include <algorithm>
#include<cstdio>
#include<sstream>
#define pow2(n) (1 << (n)
using namespace std;
struct avl_node
{
avl_node* left;
avl_node* right;
char pname[30]; //Patient Name
char fname[30]; //Father Name
int age;
int nic;
char address[20];
char disease[15];
char dname[30]; //Doctor Name
int p_id; //Pateint Id
}*root;
class AVL
{
public:
AVL();
int height(avl_node*);
int diff(avl_node*);
avl_node* r_rotation(avl_node*); //Right Rotation
avl_node* l_rotation(avl_node*); //Left Rotation
avl_node* lr_rotation(avl_node*); //Left-Right Rotation
avl_node* rl_rotation(avl_node*); //Right-Left Rotation
avl_node* balance(avl_node*);
//Functions For NIC Key
avl_node* getdatanic(avl_node*,int,char[],char[],int,int,char[],char[],char[]);
avl_node* adddatanic(avl_node*,int,char[],char[],int,int,char[],char[],char[]);
void searchbynic();
void showgreatestnic();
void showleastnic();
void showascendingnic();
void ascendingnic(avl_node*);
void showdescendingnic();
void descendingnic(avl_node*);
//Functions For ID Key
avl_node* getdataid(avl_node*,int,char[],char[],int,int,char[],char[],char[]);
avl_node* adddataid(avl_node*,int,char[],char[],int,int,char[],char[],char[]);
void searchbyid();
void showgreatestid();
void showleastid();
void showascendingid();
void ascendingid(avl_node*);
void showdescendingid();
void descendingid(avl_node*);
void delete_all(avl_node*);
~AVL();
};
答案 0 :(得分：5)
最有可能的是，您已经在root标题中定义了 - 而不是声明 - AVL.h，并且您有多个文件包含AVL.h标题（没有多少文件）如果只有一个文件包含它，则指向一个标题），因此您可以对变量root进行多次定义。
你有机会写下：
avl_node *root;
（可能包括= 0之类的初始值设定项）而不是正确的：
extern avl_node *root;
。修复是双重的：
extern（并确保没有初始值设定项）。avl_node *root;（可能是AVL.cpp，或者您用于C ++源代码的任何扩展名。）您的标题包含：
struct avl_node
{
avl_node* left;
avl_node* right;
char pname[30]; //Patient Name
char fname[30]; //Father Name
int age;
int nic;
char address[20];
char disease[15];
char dname[30]; //Doctor Name
int p_id; //Patient Id
} *root;
它需要包含：
struct avl_node
{
avl_node* left;
avl_node* right;
char pname[30]; //Patient Name
char fname[30]; //Father Name
int age;
int nic;
char address[20];
char disease[15];
char dname[30]; //Doctor Name
int p_id; //Patient Id
};
extern avl_node *root;
AVL.cpp中的代码需要有额外的行：
avl_node *root = 0;
所有东西都需要重新编译。
（我们将struct vs class的设计选择留给另一天。）