Thread: Reading from stdin and printing (Segmentation Fault)

I'm writing a program that reads from stdin and prints it back out. I'm getting a bunch of garbage then a seg fault.

Code:

   double numbers[256];
   memset (numbers, 0, sizeof (numbers));
   for (;;) {
      double num = scanf ("%255lg", numbers);
      if (num== EOF) 
         break;
   }
   for (int i = 0; i < (int)sizeof (numbers); ++i) {
      printf ("%g\n", numbers[i]);
   }

The format specifier %255lg tells scanf() to read a single floating point value, which might have a width (in terms of characters typed in) of 255 characters.

scanf() does not provide any format specifier for reading a whole array of floating point values.

Try reading one value at a time, but do that in a loop 256 times.

Also, scanf() returns an integer, not a double. The return value is not always EOF when an error occurs.

So, try looking more closely at the documentation for scanf().


sizeof(numbers) also does not yield the number of values in the array. Nor does it have any relationships to the number of values read in. In fact sizeof(numbers) in your case will probably be 2048 (8 times 256).

Originally Posted by Sorin

I'm trying to start reading code other than my own....so at first glance after your post grumpy....what about the second line? Shouldn't that "buffer" say "numbers" instead? It looks to me to be the intended operation, and I don't see where buffer is defined.

I was doing some test. Buffer in memset is suppose to be numbers. And thanks grumpy I realized it's an array of 1000 doubles. I was used to creating char pointers and never really created an array this way before.

Code:

   double numbers[1000];
   memset (numbers, 0, sizeof (numbers));
   int count = 0;
   for (int i = 0; ; ++i) {
      int return_value = scanf ("%lg", &numbers[i]);
      if (return_value == EOF) break;
      ++count;
   }
   for (int i = 0; i < count; ++i) {
      printf ("%g\n", numbers[i]);
   }