File I/O

[rachitagrawal]

I have a file to write in binary mode. Right now I am doing this as below

int main()
{
   int num;
   long long time;
   FILE *fin = fopen("test1.txt", "r");
   FILE *fout = fopen("test2.out", "wb");

   while(!feof(fin))
   {
      fscanf(fin, "%d %lld", &num, &time);
      fwrite(&num, sizeof(num), 1, fout);
      fwrite(&time, sizeof(time), 1, fout);
   }
   
   fclose(fin);
   fclose(fout);
   return 0;
}

I want to reduce the number of fwrite calls. Lets say by buffering the inputs. How to do that?

[kbw]

FILE* i/o is buffered.

[PanGalactic]

rachitagrawal wrote:

I want to reduce the number of fwrite calls.

Why?

[rachitagrawal]

@kbw But I guess they are fixed for all architecture and all OS that might not be optimal. Isn't it?

@PanGalactic: I want to reduce the overhead due to repeatitive I/O.

[kbw]

fixed for all architecture

What?

You can change the buffer size with setbuf.

[rachitagrawal]

@kbw: Buffer length.

Oh ok. I didnt have idea about the setbuf.

One more thing, I was trying to buffer it with a structure. But somehow, its not working. Just curious to know what is the problem. See if you can figure it out?

struct buffer_t
{
   int num;
   long long time;
};

int main()
{
   int num;
   long long time;
   struct buffer_t bWrite[16];
   FILE *fin = fopen("test1.txt", "r");
   FILE *fout = fopen("test2.out", "wb");

   while(!feof(fin))
   {
      fscanf(fin, "%d %lld", &num, &time);
     
      if(i  == 16)
      {
          fwrite(&bWrite, sizeof(bWrite), 16, fout);
          i == 0;
      }

      bWrite[i].num = num;
      bWrite[i].time = time;
      i++;
   }
   
   fwrite(&bWrite, sizeof(bWrite), i, fout);
   fclose(fin);
   fclose(fout)
   return 0;
}

[kbw]

Have you checked the size of int, long long and buffer_t? You'll probably find that buffer_t is larger than the sum of it's parts. You need to pack the structure to byte alignment.

[rachitagrawal]

Oh ok, I got the problem. Thank you. :)