fscanf issues

[dsotm26]

hello
i am struggling a bit with fscanf and hope someone can assist me here.

my goal is to just open a file
read each value and store and print one of two values START and FINISH

the trouble i am having is the issue of having only one
number on a line and not two.

say i have the following data file
data.dat
----------------
0
1 234
22 3456
333 4567
4444 56789
0
0

i just want to read the file and out put
start = 0 and finish = BLANK
start = 1 and finish = 234
start = 22 and finish = 3456

the problem i am having is that it prints it out mixed up
the output i get is (where finsih should be it reads the next start)
start = 0 and finish = 1
start = 234 and finish = 22
start = 3456 and finish = 4444

my code is as follows:

while ( (c = getc (fPtr)) != EOF){
fscanf(fPtr, "%d %d", &start, &finsih);
printf("start= %d and finish= %d",start,finish);
}

this also skips the first line

my question is how do i discern between a line with 2 fields VS a line with 1 field

meaning can i do a count or check on what fscanf
brings in or does fscanf return the number of fields it has read

something like (this is not true code)

open file
read file
while not EOF
fscanf(%d %d, start, finish);
if finsih has nothing then dont print out finsih
else print both out

please help im quite frustrated at C right now

[kuphryn]

I am not familiar with fscanf().

There are several solutions. In your code you use reset the temporary start and finish. If the call to fscanf() does not change variable finish, then it is a one-liner.

Kuphryn

[yiannakop]

I wrote this program and I think it works ( I use fgets and sscanf instead of fscanf):

#include <stdio.h>
#include <stdlib.h>

int main()
{
  FILE *fp;
  int START,FINISH,i,count,num_of_ints;
  char *str = (char*)malloc(100);
  fp = fopen("data.dat","r");
  if (fp)
  {
     while (fgets(str,100,fp))
     {
        count = 0;
        // count number of spaces:
        for (i=0;i<strlen(str);i++)
            if (str[i]==' ')
	count++;
        // find number of integers per line:
        num_of_ints = count + 1;
        if (num_of_ints==1)
       {
         sscanf(str,"%d",&START);
         printf("START = %d   FINISH = BLANK\n",START);
       }
       else
          if (num_of_ints==2)
	{
	   sscanf(str,"%d %d",&START,&FINISH);
	   printf("START = %d   FINISH = %d\n",START,FINISH);
	}

      }		
    fclose(fp);
  }
}

[Rabelo]

If the file is a text file you can also use sscanf to get the numbers on numeric variables. cheking the value of n2 you can see if the 2nd number is missing or not.

#include "stdio.h"

int main()
{
  FILE* infile = fopen("test.txt","rt");
  char buff[100];
  int n1,n2;

  while(fgets(buff,95,infile))
  {
    n2 = -1;
    sscanf(buff,"%d %d",&n1,&n2);
    printf("%d %d\n",n1,n2);

    if (n2 == -1) printf("2nd number is missing\n");
  }
  return 0;
}

test.txt
10
50 60
70 80
90

[Richard.J]

Ooh, this is really weird. The scanf-family of functions returns the number of items successfully read, so this seems to be the info you need. Tis is the kind of question I tend to answer with RTFM, although it is not very polite ;-)

[nsh123]

while ( (c = getc (fPtr)) != EOF){
fscanf(fPtr, "%d %d", &start, &finsih);
printf("start= %d and finish= %d",start,finish);
}

doesnt getc(fptr) eat up one character from the file (similar to fgetc)

If it doesnt that is great way of avoiding something like ungetc.

fgets followed by sscanf is the better approach.

Richard, even if fscanf returns the number of succesffull reads,
the first fscanf will return two successful reads since it shifts to the second line.

Regards