c - 输入文件时出现 SegFault

Question

这是我的代码。编辑:调用者包含在底部。

该函数读取数据文件，确定有多少行和列，然后将数据存储到 data_array 中。

int getdata(double* *data_array, int* *data_labels, int argc, char *argv[], int *items, int *attr)
{  
// filename variables
char *filename; // pointer to a string that will contain the name of the training data file.
char *result = NULL; // used with strtok() to extract each feature value given a line of delimited features.
FILE *fp; // pointer to FILE, we can use this with fgets to access each line
char line[10000];       // array of 1000 chars for storing the raw data for one observation
char delims[4];         // an array of common delimiters for data files
delims[0]='\t';
delims[1]=' ';
delims[2]=',';
delims[3]='\0';
int i, j;
// check that we have the correct number of command line arguments
if (argc < 2)
{
   printf("2usage: progname filename\n");
   return -1;
}

if (argc < 4)
{
   printf("3usage: progname filename num_labels k(nn)\n");
   return -1;
}

if (atoi(argv[2]) < 1)
{
    printf("num_labels must be a positive integer.\n");
    return -1;
}

if (atof(argv[2]) - atoi(argv[2]) > 0)
{
    printf("num_labels must be an integer.\n");
    return -1;
}

if (atoi(argv[3]) < 1)
{
   printf("k must be a positive integer.\n");
   return -1;
}

if (atof(argv[3]) - atoi(argv[3]) > 0)
{
   printf("k must be an integer.\n");
   return -1;
}

// try to open the file
filename = argv[1];
fp = fopen(filename, "r");
if (fp == NULL)
{
   printf("could not open file: %s\n", filename);
   printf("note: the filename should be the second command line argument, after the .exe file");
    return -1;
 }
 printf("reading file: %s\n", filename);

 // GET NUMBER OF ROWS AND COLUMNS OF INPUT FILE
 fgets(line, 10000, fp);
 result = strtok(line,delims);
 while(result != NULL)
 {
  (*items)++;
  result = strtok(NULL, delims);
 }  
  (*attr)++;
  while(fgets(line,sizeof(line),fp) != NULL)
  (*attr)++;

  printf("num items: %d\n", *items);
  printf("num attributes: %d\n", *attr); 


  // NOW THAT YOU HAVE FILE SIZE, ALLOCATE MEMORY TO STORE DATA
  *data_array = malloc(*items* *attr*sizeof(double));
  //*data_labels = malloc(*items*sizeof(int));
  printf("data array size = %d\n\n",*items* *attr);

  i=0;
  j=0;
  fclose(fp);
  fp = fopen(filename, "r");
  // SAVE DATA INTO DATA_ARRAY
  while (fgets(line, 10000, fp) != NULL) 
  { 

  // we break line into tokens using our delimeters list declared at the beginning of the function
  result = strtok(line,delims);
  //printf("%d\n",i);
   while(result != NULL) {
   (*data_array)[i++] = atof(result);
   //printf("%f\n",(*data_array)[i-1]);
   result = strtok(NULL, delims);
   }
   //(*data_labels)[j++] = (int)((*data_array)[--i]);
   }
   // close the file
   fclose(fp);
   return 0;
    }

    int main(int argc, char *argv[])
    {
      double *data_array = NULL;
      int *data_labels = NULL;
      int items = 0;
      int attr = 0;

      if (getdata(&data_array, &data_labels, argc, argv, &items, &attr) == -1)
      {
        printf("reading input data failed");
        return 0;
      }
      printf("PROCESS COMPLETED WITHOUT SEGFAULT");

      #ifdef CROSSVAL
      // v-fold cross-validation
      if (crossval(data_array, atoi(argv[2]), items, attr, closest_center, centers) == -1)
      {
        printf("k-means operation failed");
        return 0;
      }
      #else

      // coords holds coordinates of one new point
      int i;
      double coords[attr];
      for(i = 0; i<attr;i++)
      {
        coords[i] = atof(argv[i+4]);
      }
    /*
      // calling knn function
      if (knn(data_array, data_labels, atoi(argv[2]), atoi(argv[3]), coords, items, attr) == -1) // use a heap!
      {
        printf("knn operation failed");
        return 0;
      }
    */
      #endif

      free(data_array);
      return 0;
     }

奇怪的是这个函数在出现段错误之前输出正确。给定一个包含 2 列和 272 行的数据文件，我得到“num items: 2, num attribute: 272, data array size = 544”。但是，如果我注释掉 "printf("num attribute: ..."行之后和最后一个 fclose(fp) 行之前的所有内容，它仍然会出现段错误。它很好地完成了打印语句，然后出现了段错误，即使它后面没有重要的代码。太困惑了。

Answer 1

在 for 循环中调用 getdata() 后，程序出现段错误。

您不会检查程序是否有足够的参数，也不会读取 attr + 4 参数，无论它们是否存在。

这也是当您删除 (*attr)++ 时不会出现段错误的原因。因为这样，attr 仍为 0 并且您不会尝试读取不存在的参数。