Reading info from a file...

**tammo21** · 07-02-2003

I need some help. Either I'm wrong, or the compiler is broken. I got this program:

Code:

#include <stdio.h>
#include <stdlib.h>
main()
{
	FILE *fp;
	char death[] = "bob.txt";
	float l1=0, l2=0, l3=0, l4=0, l5=0;
	if ( (fp = fopen(death, "r")) == NULL)
	{
	printf("error opening file.");
	}
	else
	{
	fscanf(fp, "%f, %f, %f, %f, %f", &l1, &l2, &l3, &l4, &l5);
	printf("%f, %f, %f, %f, %f", l1, l2, l3, l4, l5);
	fclose(fp);
	getch();
	}
}

The file bob.txt looks like this:

Code:

123.45     87.001
100.02
0.00456    1.0005

But when the program executes, it outputs this:

123.449997, 0.000000, 0.000000, 0.000000, 0.000000

I have gone through the program over and over and can't figure out why it's not going to the next number in the file. Anyone have any ideas for me?

**Dave_Sinkula** · 07-02-2003

Consider the differences with this code.

Code:

#include <stdio.h>

int main(void)
{
   const char death[] = "bob.txt";
   FILE *fp = fopen(death, "r");
   if ( fp == NULL )
   {
      perror(death);
   }
   else
   {
      float l1=0, l2=0, l3=0, l4=0, l5=0;
      if ( fscanf(fp, "%f%f%f%f%f", &l1, &l2, &l3, &l4, &l5) == 5 )
      {
         printf("%f, %f, %f, %f, %f\n", l1, l2, l3, l4, l5);
      }
      else
      {
         puts("fscanf failed"); 
      }
      fclose(fp);
   }
   getchar();
   return 0;
}

/* my output
123.449997, 87.000999, 100.019997, 0.004560, 1.000500
*/

[EDIT]
One of the main problems was your format specifier, which expected commas. Since none were found in the input file, fscanf failed. If you had been checking return values, this would have been immediately apparent.
[/EDIT]

**tammo21** · 07-02-2003

The only real difference I can see is the "," in between the %f signals, which leads me to believe that they're fudging it up, since my program now works. Sheesh, it's always the little things.
'
Can you tell me what the commas in the fscanf function actually do and why they were messing it up?

**Dave_Sinkula** · 07-02-2003

>Can you tell me what the commas in the fscanf function actually do and why they were messing it up?

The second parameter to fscanf is a format string. The format string contains directives. If the directive is an ordinary character -- a "%," is not valid -- then the following applies:

A directive that is an ordinary multibyte character is executed by reading the next characters of the stream. If any of those characters differ from the ones composing the directive, the directive fails and the differing and subsequent characters remain unread. Similarly, if end-of-file, an encoding error, or a read error prevents a character from being read, the directive fails.

So yes, in your original code you were telling fscanf to fail if the values weren't comma-delineated.

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