C編程鏈接列表 - 無法運行程序

Question

我有一個關於C編程鏈接列表的問題。 我寫出了這段代碼，但我在運行代碼時遇到了運行時錯誤。 我是C編程新手，請大家幫忙。

• 在Project1.exe中0x00161A66引發異常：0xC0000005：訪問衝突寫入位置0xCCCCCCEC。
• Project1.exe中0x00161A66未處理的異常：0xC0000005：訪問衝突寫入位置0xCCCCCCEC。 插入Thompson時發生錯誤

下面是我正在努力的問題。我無法按字母順序打印出來。

，我做的問題是

a) Create a pointer to the start of the list called startPtr. The list is empty. 
b) Create a new node of type GradeNode that’s pointed to by pointer newPtr of type GradeNodePtr. 
Assign the string "Jones" to member lastName and the value 91.5 to member 
grade (use strcpy). Provide any necessary declarations and statements. 
c) Assume that the list pointed to by startPtr currently consists of 2 nodes—one containing 
"Jones" and one containing "Smith". The nodes are in alphabetical order. Provide 
the statements necessary to insert in order nodes containing the following data for 
lastName and grade: 
"Adams" 85.0 
"Thompson" 73.5 
"Pritchard" 66.5 

這是代碼：

所有的

#include <stdio.h> 
    #include <string.h> 
    int main(){ 
    struct gradeNode{ 
    char lastName [20]; 
    double grade; 
    struct gradeNode *nextPtr; 
    }; 

    typedef struct gradeNode GradeNode; 
    typedef GradeNode *GradeNodePtr; 
    GradeNodePtr startPtr = NULL; 
    GradeNodePtr currentPtr = NULL; 
    GradeNodePtr previousPtr = NULL; 

    GradeNodePtr newPtr; 
    if (newPtr != NULL){ 
     newPtr = malloc(sizeof(GradeNode)); 
     strcpy(newPtr -> lastName,"Jones"); 
     newPtr -> grade = 91.5; 
     newPtr -> nextPtr = NULL; 

    } 

    //Insert "Adams" 
//previousPtr is NULL, and currentPtr points to the first node in the list. 
    newPtr -> nextPtr = currentPtr; 
    startPtr = newPtr; 


    newPtr = malloc(sizeof(GradeNode)); 
    strcpy(newPtr -> lastName,"Smith"); 
    newPtr -> grade = 40.5; 
    newPtr -> nextPtr = NULL; 

    newPtr -> nextPtr = currentPtr; 
    startPtr = newPtr; 

    newPtr = malloc(sizeof(GradeNode)); 
    strcpy(newPtr -> lastName,"Adams"); 
    newPtr -> grade = 85.0; 


//Insert "Thompson" 
//previousPtr points to the last node in the list(containing Smith") and currentPtr is NULL 
    newPtr -> nextPtr = currentPtr; //or newPtr -> nextPtr = NULL 
    previousPtr -> nextPtr = newPtr; 

    newPtr = malloc(sizeof(GradeNode)); 
    strcpy(newPtr -> lastName,"Thompson"); 
    newPtr -> grade = 73.5; 

//Insert "Pritchard" 
//previousPtr points to the node containing "Jones" and currentPtr points to the node contaiing "Smith" 
    newPtr -> nextPtr = currentPtr; 
    previousPtr -> nextPtr = newPtr; 

    newPtr = malloc(sizeof(GradeNode)); 
    strcpy(newPtr -> lastName,"Pritchard"); 
    newPtr -> grade = 66.5; 

    currentPtr = startPtr; 
    while(currentPtr!=NULL){ 
     printf("Lastname = %s\nGrade = %.1f\n\n",currentPtr->lastName,currentPtr->grade); 
     currentPtr = currentPtr->nextPtr; 
    } 






} 

Answer 1

首先，你應該讓你的邏輯清晰。
這裏有一些你可以使用的提示。

1. 您不包括stdlib.h其中包括malloc的定義。在這種情況下，編譯器將發出一條警告消息
2. 創建newPtr後，您正在檢查NULL。它最初將會是NULL或者一些垃圾值。只有當它不是NULL時，纔會分配內存
3. 您沒有正確鏈接節點。首先在一篇論文中闡述你的邏輯，然後嘗試編寫它。