結構鏈接列表分段 - 錯誤

Question

我剛剛開始使用我的實驗室，在這裏我計算其信息存儲在結構鏈接列表中的課程的GPA。到目前爲止，我試圖打印出所有課程信息，以確保它們已被正確初始化並添加到鏈接列表中。

我遇到了問題，但因爲我一直在收到分段錯誤。我明白分段錯誤的含義，但我不知道我犯了什麼錯誤。任何幫助，將不勝感激。

#include <stdio.h> 
#include <stdlib.h> 
#include <ctype.h> 
#include <string.h> 

#define MAX_CLASSES 20 


/* Function Prototypes */ 
struct course * initcourse(int, char *, char *, float, char *, char *); 
void add(struct course *); 

/* Definition of a data node holding course information */ 
    struct course { 
    int term; 
    char name[15]; 
    char abbrev[20]; 
    float hours; 
    char grade [4]; 
    char type[12]; 
    struct course *next; 
    }; 


/* head points to first node in list, end points to last node in list */ 
/* initializes both to NULL, no nodes yet */ 
struct course *head = (struct course *) NULL; 
struct course *end = (struct course *) NULL; 


/* Initializes a node, allocates memory for the node, and returns  */ 
/* a pointer to the new node. Must pass correct parameters.   */ 
struct course * initcourse(int term, char *name, char *abbrev, float hours, char *grade, char *type) 
{ 
    struct course *ptr; 
    ptr = (struct course *) calloc(1, sizeof(struct course)); 
    if(ptr == NULL) 

    return (struct course *) NULL; 

    else 
    { 
     ptr->term = term; 
     strcpy(ptr->name, name); 
     strcpy(ptr->abbrev, abbrev); 
     ptr->hours = hours; 
     strcpy(ptr->grade, grade); 
     strcpy(ptr->type, type); 
     return ptr; 
    } 
} 


/* This adds a node to the end of the list. You must allocate a node and */ 
/* then pass its address to this function        */ 
void add(struct course *new) 
{ 
    if (head == NULL) 
    { 
     head = new; 
    } 
    else 
    { 
     end->next = new; 
     end = new; 
    } 
} 

/* Prints all information in a node */ 
void printnode(struct course *ptr) 
{ 
    printf("Term ->%d\n", ptr->term); 
    printf("Name ->%s\n", ptr->name); 
    printf("Abbreviation ->%s\n", ptr->abbrev); 
    printf("Hours ->%f\n", ptr->hours); 
    printf("Grade ->%s\n", ptr->grade); 
    printf("Type ->%s\n", ptr->type); 
} 




/* Prints List of Nodes */ 
void printlist(struct course *ptr) 
{ 
    while(ptr != NULL) 
    { 
     printnode(ptr); 
     ptr = ptr->next; 
    } 
} 

/* Calculates GPA */ 
/* float gpa (struct course *ptr) */ 
/* { */ 
/* float totalhours; */ 
/* float gpa; */ 
/* float gradepoints; */ 

/* while (ptr != NULL) */ 
/*  { */ 
/*  totalhours += (ptr->hours); */ 
/*  gradepoints = (ptr->hours * ptr->grade); */ 
/*  } */ 
/* gpa = (gradepoints /ptr->hours); */ 
/* } */ 



int main() 
{ 

    int term; 
    char name[15]; 
    char abbrev[20]; 
    float hours; 
    char grade[4]; 
    char type[12]; 
    float gpa; 
    struct course *ptr; 

    struct course course1, course2, course3; 

    course1.term = 1234; 
    strcpy(course1.name,"cse1234"); 
    strcpy(course1.abbrev,"systems"); 
    course1.hours = 4; 
    strcpy(course1.grade,"A"); 
    strcpy(course1.type,"GEC"); 


    ptr = initcourse(course1.term, course1.name, course1.abbrev, course1.hours, course1.grade, course1.type); 

    struct course *head, *ptr2; 
    head = ptr; 
    // ptr2 = ptr; 

    add(ptr); 

    course2.term = 4332; 
    strcpy(course2.name,"cse4332"); 
    strcpy(course2.abbrev,"Database"); 
    course2.hours = 4; 
    strcpy(course2.grade,"B"); 
    strcpy(course2.type,"Technical"); 

    ptr2 = initcourse(course2.term, course2.name, course2.abbrev, course2.hours, course2.grade, course2.type); 

    add(ptr2); 

    printlist(head); 



} 

Answer 1

void add(struct course *new) 
{ 
    if (head == NULL) 
    { 
     head = new; 
    } 
    else 
    { 
     end->next = new; 
     end = new; 
    } 
} 

您需要設置end到new插入第一個節點（當head == NULL）時，否則你添加更多的節點時，提領一空指針。

而且在initcourse，你應該到next成員設置爲NULL，因爲它不是由所有位0是一個空指針表示的標準保證的（它非常可能是，但沒有保證）。

此外，

struct course *head, *ptr2; 
head = ptr; 

聲明瞭一個新的局部變量head是陰影的全球之一，而不是直接分配給head（即使是錯誤的），你應該叫add(ptr);。

Answer 2

您不初始化next指針，所以最後一個元素包含一個壞指針，指向一些垃圾。您也可以不初始化end。

另一個問題（不涉及崩潰）是這個代碼將創建一個重複的條目：

head = ptr; 
add(ptr); 

還有一些其他的問題。你真的應該得到一個調試器，看看發生了什麼。