Question

我有以下输入文件：

WO98EKOYMPCAUEWT0 Honda Civic 2011 4
7W32UAERZFBCB3S6P Chevrolet Tahoe 2011 6
DNU7XQO8LLA9I6YFX Toyota Tercel 2012 4
DNU7XQO8LLA9I6YFX Toyota Tercel 2012 4
DNU7XQO8LLA9I6YFX Toyota Tercel 2012 4
7W32UAERZFBCB3S6P Chevrolet Tahoe 2011 6

这实际上是我们交付的一项任务，我已经挣扎了几天而没有结果。

读取每一行并将第二，第三和第四的值放在结构中。
之后添加一个新列，它是基于上面3列的出现次数。
按秒，第三和第四排序数据。然后将它们输出到文件中。

到目前为止，这是我的代码：

struct Car
{
       char *CarMake;
       char *CarModel;
       char *CarMakeYear;
       int Occurances;
};

int main(int argc, char *argv[])
{
  //File related
  FILE *inputFile, *outputFile; 
  char fileName[] = "";

  //Struct related
  int carCounter = 0;
  struct Car cars[50];

  struct Car car;
  car.CarMake  = (char*)malloc( 200 *sizeof(char));
  car.CarMakeYear  = (char*)malloc( 200 *sizeof(char));
  car.CarModel  = (char*)malloc( 200 *sizeof(char));
  car.Occurances = 0;  

  printf("Please enter file name:",  fileName);
  scanf("%s",fileName);
  inputFile = fopen(fileName,"r"); 

  while(fscanf(inputFile, "%*s %s %s %s %*s\n",car.CarMake, car.CarModel,car.CarMakeYear ) != EOF)
  {         
   cars[carCounter].CarMake = car.CarMake;                     
    carCounter++;
  }
  fclose(inputFile);

  int i=0;
  for(i=0;i<6;i++)
   printf("%s %s %s \n", cars[i].CarMake, cars[i].CarModel,cars[i].CarMakeYear);

  system("PAUSE");  
  return 0;
}

上面的printf将采用最后一个数组值并保持打印，这意味着它无法正常工作。有人请帮忙，我要到午夜才提交。

Answer 1

cars[carCounter].CarMake = car.CarMake;

这一行是问题所在。在C中，您不能简单地使用赋值运算符复制字符串。您必须为字符串分配一个新缓冲区并将其复制：

cars[carCounter].CarMake = malloc(strlen(car.CarMake) + 1); // plus one to include the null-terminator
strcpy(cars[carCounter].CarMake, car.carMake);

根据您使用的平台/编译器，您可以使用strdup函数，它基本上完全相同：

cars[carCounter].CarMake = strdup(car.CarMake);

完成后不要忘记free记忆。

修改

从用户输入中获取文件名还有另一个问题。 char fileName[] = "";行不会为实际文字留下任何空间 - 请尝试char fileName[100];之类的内容。即使现在有效，也不能保证继续工作;依靠未定义的行为，永远不会安全。

Answer 2

我会这样写：

struct Car
{
       char *CarMake;
       char *CarModel;
       char *CarMakeYear;
       int Occurances;
};

int main(int argc, char *argv[])
{
  //File related
  FILE *inputFile, *outputFile; 
  char fileName[] = "";

  //Struct related
  int carCounter = 0;
  struct Car cars[50];

  struct Car car;
  car.CarMake  = (char*)malloc( 200 *sizeof(char));
  car.CarMakeYear  = (char*)malloc( 200 *sizeof(char));
  car.CarModel  = (char*)malloc( 200 *sizeof(char));
  car.Occurances = 0;  

  printf("Please enter file name:",  fileName);
  scanf("%s",fileName);
  inputFile = fopen(fileName,"r"); 

  while(fscanf(inputFile, "%*s %s %s %s %*s\n",car.CarMake, car.CarModel,car.CarMakeYear ) != EOF)
  {         

   cars[carCounter].CarMake = car.CarMake;                     
  //-- change starts here
  // the values of the car struct being pointed to by the current carCounter array placeholder
  // you allocate a new car so that you won't be touching the old ones.
  car.CarMake  = (char*)malloc( 200 *sizeof(char));
  car.CarMakeYear  = (char*)malloc( 200 *sizeof(char));
  car.CarModel  = (char*)malloc( 200 *sizeof(char));
  //-- change ends here
    carCounter++;
  }
  fclose(inputFile);

  int i=0;
  for(i=0;i<6;i++)
   printf("%s %s %s \n", cars[i].CarMake, cars[2].CarMake,cars[3].CarMake);

  system("PAUSE");  
  return 0;
}

将输入文件读入struct并对数据进行排序？

2 个答案: