C：讀取二進制文件

Question

我知道fopen可以執行「rb」（讀取二進制文件）和「wb」（寫入二進制文件）來讀寫二進制文件。這是我對讀這樣的文件：

（編輯：這裏的結構對於那些想知道誰）

typedef struct student 
{ 
    char lname[ 10 ], initial[1], fname[ 10 ]; 
    unsigned long SID; 
    float GPA; 
    struct student *next; 
} SREC; 

這裏是我的變量：

FILE *fptr, *fout; 
SREC *temp = NULL; 
SREC *firstName = NULL; 
SREC *lastName = NULL; 
SREC *studentID = NULL; 
SREC *grade = NULL; 
char lname[10] = ""; 
char fname[10] = ""; 
char mid[1]; 
unsigned long SID = 0; 
float GPA = 0.0; 
char temp2[100]; 
char inString[100]; 
int servercmd = 0; 
int fileOpen = 0; 
int totalCount = 0; 

...以下是主要內容：

if ((fptr = fopen("data", "rb+")) == NULL) 
{ 
    printf("No file detected. Creating...\n"); 
    if ((fout = freopen("data","wb+",stdout)) == NULL) 
    { 
     fprintf(stderr,"Cannot generate file!\n"); 
     exit(1); 
    } 
    else 
     fclose(fout); 
} 
else 
{ 
    if (!feof(fptr)) 
    { 
     fileOpen = 1; 
     insert_student(&temp," "," "," ",00000,0.00,1); 
     while(!feof(fptr)) 
     { 
      /* fscanf(fptr,"%s %s %c %d %f",lname,fname,&mid[0],&t1,&GPA); */ 

      fread(&temp,sizeof(SREC),1,fptr); 

      /* Make sure it's not empty. */ 
      printf("Is it strcmp?\n"); 
      if (strcmp(temp->lname," ") != 0) 
      { 
       insert_student(&firstName,temp->lname,temp->initial,temp->fname,temp->SID,temp->GPA,1); 
       insert_student(&lastName,temp->lname,temp->initial,temp->fname,temp->SID,temp->GPA,2); 
       insert_student(&studentID,temp->lname,temp->initial,temp->fname,temp->SID,temp->GPA,3); 
       insert_student(&grade,temp->lname,temp->initial,temp->fname,temp->SID,temp->GPA,4); 
       totalCount++; 
       printf("%d\n",totalCount); 
      } 
     } 
     printf("Finished reading.\n"); 
    } 
    else 
    { 
     printf("File is empty.\n"); 
    } 
} 

這裏是我分配內存來存儲信息的地方。

void insert_student(SREC **studentPtr, char last[10], char init[1], char first[10], unsigned long SID, float GPA, int mode) 
{ 
SREC *newNode; 
SREC *previous; 
SREC *current; 

newNode = (SREC*)malloc(sizeof(SREC)); 

if(newNode != NULL) /*Make sure memory was available*/ 
{ 
    strcpy(newNode -> lname,last); 
    strcpy(newNode -> initial,init); 
    strcpy(newNode -> fname,first); 
    newNode->SID = SID; 
    newNode->GPA = GPA; 
    newNode->next = NULL; 

    previous = NULL; 
    current = *studentPtr; 

    /* Traverses list until end or larger data is found. 
    * If order doesn't matter, only append to the end by 
    * removing second condition or insert at the beginning 
    * in constant time. */ 
    if (mode == 1) /*first name*/ 
    { 
     while(current != NULL && strcmp(first,current->fname) > 0) 
     { 
      previous = current; 
      current = current -> next; 
     } 
    } 
    else if (mode == 2) 
    { 
     while(current != NULL && strcmp(last,current->lname) > 0) 
     { 
      previous = current; 
      current = current -> next; 
     } 
    } 
    else if (mode == 3) 
    { 
     while(current != NULL && SID > current->SID) 
     { 
      previous = current; 
      current = current -> next; 
     } 
    } 
    else if (mode == 4) 
    { 
     while(current != NULL && GPA > current->GPA) 
     { 
      previous = current; 
      current = current -> next; 
     } 
    } 

    if (previous == NULL) /*newNode is placed at the beginning*/ 
    { 
     newNode -> next = *studentPtr; 
     *studentPtr = newNode; 
    } 
    else /*newNode is placed in middle or end*/ 
    { 
     previous -> next = newNode; 
     newNode -> next = current; 
    } 

} 
else 
{ 
    printf("%s not inserted\n",last); 
} 
} 

我的程序在while循環之後的fread部分發生了段錯誤。數據保存了二進制與

fwrite(&lastName,sizeof(SREC),totalCount,fout); 

每次記錄被放進去，TOTALCOUNT上升，每一條記錄被刪除時，它的股價下跌。所有這些東西的作品。它只是讀取字節並試圖使它不會導致我遇到問題的seg故障。我究竟做錯了什麼？

再次重申，這是問題的代碼這是越來越段錯誤：

fread(&temp,sizeof(SREC),1,fptr); 

Answer 1

此行

fread(&temp,sizeof(SREC),1,fptr); 

被數據讀入的temp位置。您想要將數據讀入您已擁有（可能）分配給溫度的內存中。刪除&

fread(temp,sizeof(SREC),1,fptr); 

Answer 2

問題是循環條件：

while(!feof(fptr)) 

feof()只返回非零它，你讀過文件結尾，而不是當文件指針爲時結束文件。這意味着你的循環將運行一次比它應該。