循環指針數組

Question

我正在寫一個指針和結構數組的代碼。 代碼是：

struct Student_List{ 
    int roll; 
    char name[20]; 
    int mark1; 
    int mark2; 
    int mark3; 
    struct Student_List *next; 
}; 
struct Student_List *Class[] = { NULL };// to generate student's list for various classes. 
struct Student_List *current =NULL; 

struct Student_List * check(int rollNo, int classNo) 
{ 

struct Student_List *temp=NULL; 
temp=Class[classNo]; 

while (temp!=NULL) { 
    if(temp->rollNo == rollNo) 
    { 
     //element is found 
     return temp; 
    } 

    temp = temp->next; 
}  
if(temp==NULL) 
{ 
    //element not found 
    return NULL; 
} 
//scan serially and if found return address of that node 
//if no element found return NULL 

} 

//add elements to list pointed by Class 
struct Student_List * add(char studentName, int rollNo,int classNo) 
{ 
    struct Studen_List *newNode=(struct Student_List *)malloc(sizeof(struct Student_List)); 
if (newNode == NULL) { 
     printf("malloc failed\n"); 
     } 

newNode->roll=rollNo; 
strcpy(newNode->name,studentName); 
newNode->mark1=0; 
newNode->mark2=0; 
newNode->mark3=0; 
struct Student_List *temp = NULL, *previous = NULL; 

temp=Class[classNo]; 
prev = temp; 
} 

if(temp==NULL) 
{ 
    Class[classNo]=newNode; 
    return Class[classNo]; 


} 

while(temp!=NULL) 
{ 
    prev=temp; 
    temp=temp->next; 
} 

prev->next=newNode; 
return newNode; 
//add node to end of the list 
} 

void Delete_List(struct Student_List *temp) 
{ 
delete []temp; 
//temp = NULL; 

/*while(temp!=NULL) 
{ 
    struct Student_List *del=temp; 
    temp=temp->next; 
    free(del); 

}*/ 
} 

int main(); 
{ 
int classNo,rollNo,i; 
char *name; 

printf("\nEnter Class No: "); 
scanf("%d",&classNo); 
printf("\nEnter Name: ") 
gets(name); 
printf("\nEnter Roll No: "); 
scanf("%d",&rollNo); 


current = check(rollNo,classNo); 

if(current == NULL){ 
current = add(name,rollNo,classNo); 
} 
// others is the marks data fetched from file and calculations. 
// this code is enough to reproduce my error. 

for(int i=0;i<10;i++) 
{ 
    Delete_List(Class[i]); 
} 
    return; 
} 

問題： 當我指定值和執行計算，結果是錯的。在調試時，我發現我的Class[3]的起始地址與Class[1]->nextRoll->nextRoll;相同

我無法刪除它。請幫我刪除循環。 歡迎提供任何有關語法或建議的幫助。

Answer 1

您不得使用malloc，用new：

struct Student_List{ 
    int roll; 
    char name[20]; 
    int mark1; 
    int mark2; 
    int mark 3; 
    Student_List *nextRoll; 
}; 

Student_List * Class[] = { NULL }; 

int main(); 
{ 
    // various initializations 

    // for each new student, do this 
    Student_List *newNode=new Student_List; 
    newNode->next = Class[0]; // 0 is the Class of the student 
    Class[0] = newNode; 

    // code to fetch data from text file and perform calculations. 

    // do not delete Class; !! 
} 

請注意，你的做法是不對的，你應該使用STL儘可能。例如：

struct Student { 
    int roll; 
    std::string name; 
    int mark1; 
    int mark2; 
    int mark3; 
}; 

typedef std::list<Student> Class; 

typedef std::map< std::string, Class > Classes; 
Classes classes; 

int main() 
{ 
    Student s; 
    s.name = "Daniel"; 
    // ... 

    classes[ "1b" ].push_back(s); // Add student to a class "1b". 
}