c - 多次使用 realloc()

Question

以下哪一项更可取

file=fopen(argv[1],"r");
arr=(unsigned int *)malloc(4);

while(!feof(file))
{
  ++arr_size;
  arr=(unsigned int *)realloc(arr,arr_size*sizeof(unsigned int)
  fscanf(file,"%u\n",&arr[arr_size-1]);
}
fclose(file);

或这个

arr=(unsigned int *)malloc(some_size*sizeof(unsigned int));
file=fopen(argv[1],"r");
arr=(unsigned int *)malloc(4);

while(!feof(file))
{
  ++arr_size;
  fscanf(file,"%u\n",&arr[arr_size-1]);
}
fclose(file);

Answer 1

为什么不是第三种方法——打开文件时计算出需要多少内存？