C++ 已在 main.obj 中定义
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Already defined in main.obj
提问by laura
This is the code for my problem and i get 4 errors:
这是我的问题的代码，我收到 4 个错误：
- student.obj : error LNK2005: "struct Node * admitedFirstNode" (?admitedFirstNode@@3PAUNode@@A) already defined in main.obj
- student.obj : error LNK2005: "struct Node * allFirstNode" (?allFirstNode@@3PAUNode@@A) already defined in main.obj
- student.obj : error LNK2005: "struct Node * rejectedFirstNode" (?rejectedFirstNode@@3PAUNode@@A) already defined in main.obj
- pb4_OOP_lab1\Debug\pb4_OOP_lab1.exe : fatal error LNK1169: one or more multiply defined symbols found
- student.obj : error LNK2005: "struct Node * allowedFirstNode" (?admitedFirstNode@@3PAUNode@@A) 已经在 main.obj 中定义
- student.obj : error LNK2005: "struct Node * allFirstNode" (?allFirstNode@@3PAUNode@@A) 已经在 main.obj 中定义
- student.obj : error LNK2005: "struct Node * deniedFirstNode" (?rejectedFirstNode@@3PAUNode@@A) 已经在 main.obj 中定义
- pb4_OOP_lab1\Debug\pb4_OOP_lab1.exe：致命错误 LNK1169：发现一个或多个多重定义的符号
#include "students.h" //main
int main()
{
for(int i=0;i<NR_STUDENTS;i++)
{
Student *s1=new Student;
cout<<"Enter name: ";
getline(cin,s1->name);
cout<<"Enter garde: ";
cin>>s1->grade;
cin.ignore();
addStudent(s1);
delete s1;
}
}
#include "students.h" //students.cpp
void AddNodeToList(Node *firstNode, Student *studToAdd)
{
Node *nodeToAdd=new Node;
nodeToAdd->student=studToAdd;
nodeToAdd->next=NULL;
if(firstNode==NULL)
{
firstNode=nodeToAdd;
}
else
{
Node *temp;
temp=firstNode;
while(temp->next != NULL)
{
temp=temp->next;
}
temp->next=nodeToAdd;
}
}
void addStudent(Student *studentToAdd)
{
AddNodeToList(allFirstNode,studentToAdd);
}
void split()
{
Node *temp=allFirstNode;
while(temp->next != NULL)
{
Student *currentStud=temp->student;
if(currentStud->grade < GR)
{
AddNodeToList(rejectedFirstNode,currentStud);
}
else
{
AddNodeToList(admitedFirstNode,currentStud);
}
}
}
void print(Node *firstNode)
{
if(firstNode==NULL)
{
return;
}
else
{
Node *temp=firstNode;
Student *current=temp->student;
while(temp->next != NULL)
{
cout<<"----------------------------------------------"<<endl;
cout<<"Student name: "<<current->name<<endl;
cout<<"Student grade: "<<current->grade<<endl;
}
}
}
#include <iostream> //students.h
#include <string>
using namespace std;
const int NR_STUDENTS=5;
const double GR=5.0;
struct Student
{
string name;
double grade;
};
struct Node
{
Student *student;
Node *next;
};
Node *allFirstNode;
Node *admitedFirstNode;
Node *rejectedFirstNode;
void addStudent(Student *studentToAdd);
void split();
void sort();
void print();
回答by Luchian Grigore
The definition Node * rejectedFirstNode;in a header file leads to a multiply defined symbol because all translation units that include that header will generate a symbol for it. Instead, in the header, have
Node * rejectedFirstNode;头文件中的定义会导致多重定义的符号，因为包含该头文件的所有翻译单元都会为其生成一个符号。相反，在标题中，有
//students.h
extern Node * rejectedFirstNode;
and move the definition in a single cpp file:
并将定义移动到单个 cpp 文件中：
//students.cpp
Node * rejectedFirstNode;
It also seems like you're writing C code. Why is this tagged C++? If you're unaware of all C++ has to offer, read a good introductory book.
您似乎也在编写 C 代码。为什么这个标记为 C++？如果您不了解 C++ 所提供的所有内容，请阅读一本很好的介绍性书籍。
回答by gogoprog
You are declaring variables in students.h and students.h is included in both main.cpp and student.cpp.
您在 student.h 中声明变量，而 student.h 包含在 main.cpp 和 student.cpp 中。
You should avoid declaring variables in headers file.
您应该避免在头文件中声明变量。
Try to put following code into students.cpp :
尝试将以下代码放入 Students.cpp 中：
Node *allFirstNode;
Node *admitedFirstNode;
Node *rejectedFirstNode;
回答by Olaf Dietsche
You have admitedFirstNode, allFirstNodeand rejectedFirstNodedefined in the header file. This defines it in every cpp, that includes the "students.h" file.
你有admitedFirstNode，allFirstNode并rejectedFirstNode在头文件中定义。这在每个 cpp 中定义了它，包括“students.h”文件。
Split the declaration and definition. Declare them in "students.h":
拆分声明和定义。在“students.h”中声明它们：
extern Node *allFirstNode;
extern Node *admitedFirstNode;
extern Node *rejectedFirstNode;
and in "students.cpp" define the variables:
并在“students.cpp”中定义变量：
Node *allFirstNode;
Node *admitedFirstNode;
Node *rejectedFirstNode;
