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Already defined in main.obj

This is the code of my problem, and I get 4 errors:

  • student.obj: LNK2005 error: "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: LNK2005 error: "struct Node * rejectFirstNode" (? rejectFirstNode @@ 3PAUNode @@ A) already defined in main.obj
  • pb4_OOP_lab1 \ Debug \ pb4_OOP_lab1.exe: fatal error LNK1169: one or more characters were found with several values
#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();
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3 answers

Definition Node * rejectedFirstNode; in the header file results in a repeatedly defined character, because all translation units that include this heading will generate a character for it. Instead in title

 //students.h extern Node * rejectedFirstNode;

and move the definition in the file to one cpp :

 //students.cpp Node * rejectedFirstNode;

It also seems like you are writing C code. Why is this tagged C ++? If you don't know what C ++ offers, read a good introductory book .

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You declare variables in students.h and students.h is included in both main.cpp and student.cpp.

You should avoid declaring variables in the header file.

Try entering the following code in students.cpp:

 Node *allFirstNode; Node *admitedFirstNode; Node *rejectedFirstNode;
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You have admitedFirstNode , allFirstNode and rejectedFirstNode defined in the header file. This defines it in every cpp that includes the students.h file.

Separate declaration and definition. Declare them in "students.h":

 extern Node *allFirstNode; extern Node *admitedFirstNode; extern Node *rejectedFirstNode;

and in "students.cpp" define the variables:

 Node *allFirstNode; Node *admitedFirstNode; Node *rejectedFirstNode;
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