c - 如何解决C中读取/写入二进制文件时的段错误

Question

这是我尝试写入副本并从二进制文件读取的结构定义

   typedef struct carType Car;
struct carType {
   int vehicleID;
   char make[20];
   char model[20];
   int year;
   int mileage;
   double cost;
   Car *next;
};

这是我写入二进制文件的代码(汽车状态)

   void writeBinFile(Car *headPointer)
{
     char fileName[20];
     //prompt user for name of textfile to print to 
    scanf("%s", fileName);
    FILE *ftp;
    Car *start =  headPointer->next;
    ftp = fopen(fileName, "wb");
    char separator = '0';
    while(start != NULL)
    {
       //write out 1 cell of data, cell contains 4 bytes
        fwrite(&start->year,sizeof(int), 1, ftp);
        fwrite(start->make,sizeof(char), strlen(start->make), ftp);
        fwrite(&separator, sizeof(char), 1, ftp); 
        fwrite(start->model, sizeof(char), strlen(start->make), ftp);
        fwrite(&separator, sizeof(char), 1, ftp);
        fwrite(&start->cost, sizeof(float), 1, ftp);
        fwrite(&start->mileage, sizeof(float),1,ftp);
        fwrite(&start->vehicleID, sizeof(int), 1, ftp);
        start = start->next;
    }
    fclose(ftp);
}

这是我从二进制文件读取的代码(到汽车的状态)

    void readFromBinFile(Car *headPointer)
{
      char fileName[20];
     //prompt user for name of textfile to print to 
    scanf("%s", fileName);
    FILE *ftp;
    Car *previous =  headPointer;
    ftp = fopen(fileName, "rb");
    Car *current;
    //go until the end of file is reached
    while(!feof(ftp))
    {
            current = (Car *)malloc(sizeof(Car));
            previous->next = current;
             //program receives 1 cell, that cell contains 4 bytes
             fread(&current->year, sizeof(int),1,ftp);
             printf("%d\n",current->year);
             char make[25];
             int count = 0;
             char oneAtATime= 'a';
             while(oneAtATime != '0') 
             { 
                    fread(&oneAtATime, sizeof(char),1,ftp);
                   if(oneAtATime!='0')
                   {
                      make[count] = oneAtATime;
                        count++;
                   }
            } 
            make[count] = 0;
           strcpy(current->make, make);
             char model[25];
              count = 0;
              oneAtATime= 'a';
             while(oneAtATime != '0') 
             { 
                    fread(&oneAtATime, sizeof(char),1,ftp);
                   if(oneAtATime!='0')
                   {
                      model[count] = oneAtATime;
                        count++;
                   }
            } 
            model[count] = 0;
           strcpy(current->model, model);
           fread(&current->cost, sizeof(float),1, ftp);
           fread(&current->mileage, sizeof(int),1,ftp);
           fread(&current->vehicleID, sizeof(int),1,ftp);
         previous = previous->next;
    } 
    fclose(ftp);
} 

上次我因未向新车分配内存而出现段错误 Why am I getting a segmentation failure? 。这次我一定要这么做。我查了这个Segmentation fault when reading a binary file into a structure和 Segmentation fault while reading binary file in C但我的字段是值，而不是指针。有人看到一个明显的问题吗？每当我尝试运行此程序时，我都无法测试任何内容，我收到该错误。问题似乎是读取，但我不确定写入中的某些代码是否导致读取失败

Answer 1

'0' 不是空终止符。 0 或 '\0' 是(请注意第一个缺少引号，第二个缺少转义字符)。 '0' 的值为 48，而不是零。

这些是有效的选项。

char separator = 0;

或

char separator = '\0';

您有一个错误:

fwrite(start->model, sizeof(char), strlen(start->make), ftp);   // 'make' size used to write 'model'

其次，您可以简化代码，而不是将分隔符 null 作为单独的步骤编写，只需写出完整的字符串，包括 null 终止符。

fwrite(start->make, 1, strlen(start->make) + 1, ftp);

但是，您打算如何读回字符串？您将使用什么函数调用来读取二进制字符串(可能是可变长度且带有空终止符)？更好的方法是使用 sizeof 而不是 strlen 来写入填充缓冲区。

fwrite(start->make, 1, sizeof(start->make), ftp);

但是，即使这样也很脆弱，因为如果您的结构成员从固定字符数组更改为字符串(指针)，则 sizeof() 将默默返回不同的值。使用常量会更安全。

const int SMALL_STRING_LEN = 20;
const int MAKE_LEN = SMALL_STRING_LEN;
const int MODEL_LEN = SMALL_STRING_LEN;

char make[MAKE_LEN];
char make[MODEL_LEN];

fwrite(start->model, 1, MODEL_LEN, ftp);
fwrite(start->make, 1, MAKE_LEN, ftp);