I am writing a program which uses fscanf to read data from a file.  This
program is a stack of "cars" and I first read the tag #, followed by
whether it's an arrival or departure (on arrival-it is stored in a stack
called garage, on departure-it is found and stored in another stack
called free_list).  The problem I'm having is, the instructor said we
need to error check extensively (including for "extra" data in the input
file)...for example...a good data line might read...
1234a
signifying car tag # 1234 is an arrival...
however, what do you do if you have...
1234ac
here is the statement I'm using...

status = fscanf (inFilePtr, "%4d%c%c", &tag_num, &enter_exit, &cr);
/* check status to confirm fscanf is successful */
if (status != 3 || cr != '\n')
{
        fprintf (outFilePtr, "%d%c", tag_num, enter_exit);
        fprintf (outFilePtr, "Invalid input---no action taken.\n");
        fprintf (outFilePtr, "Moving to next line of data...\n");

The problem here is, that when I return back to that fscanf statement in
my loop on the next pass, fscanf DOESN'T skip to the next line of data in
the input file or even to the extra character (in this case, the "c" in
1234ac).  As a matter of fact, it doesn't appear to do anything at all!
Any assistance is GREATLY appreciated...

signed...
frustrated
--

......

(Sorry, had to remove part of the original post because my network won't
post when there's more quoted text than new text).

Lots of people have problems using fscanf.
See the FAQ questions 12.17, 12.18, 12.20
The usual more controllable way is to get a line of data with fgets
and then use sscanf, strtol, atoi etc. to decipher what's in it.

--
Oliver Walter
Marconi Electronic Systems, Dynamics Division
Stanmore  HA7 4LY,  U.K.

--

My preference would be to use fgets() to read in an entire line, then
use sscanf to pull out the relevant fields.  You need to familiarise
yourself with the whole library not just the most popular (and often
overused) functions.

--
Francis Glassborow
--

In such a situation, I recommend:
 1. Use fgets() to read the file line-by-line.
 2. Use sscanf() to parse the lines after you read them.

That way, when a parse error occurs you have the data in your hands to
include in an error message, write to an exception file for manual
cleanup and reprocessing, or whatever else you want.  And you don't have
to worry about re-synching with the file to continue.
--

I am a student of C myself, but does flush help at al?  ERIK

--

Well, first I would like to point out one of those things they don't teach
you in these classes, to wit, that the entire scanf() family of functions
is a tool of Satan!  Satan, I say!  I never could get used to the odd
newline handling (or lack thereof) in these functions.  In a case like
this I would probably get the whole line from the file using fgets(), then
parse each field seperately.  Be warned-the parsing part can get ugly if
you do this, if the numeric field is variable in length.  It should work
though, and "ugly, but it works" is the kind of code C programming is all
about ;).

-W. Roth

--

Not during input, i.e. when reading a file; its effect is undefined.
It might sometimes help during output (and it's called fflush).

--
Oliver Walter
Marconi Electronic Systems, Dynamics Division
Stanmore  HA7 4LY,  U.K.

--

writes
Of course because it leaves the problem in the input buffer until you
remove the relevant character.

No.  Try
while(getchar() != '\n');
Which should read up to an including the carriage return.

Francis Glassborow      Chair of Association of C & C++ Users
64 Southfield Rd
Oxford OX4 1PA          +44(0)1865 246490
All opinions are mine and do not represent those of any organisation
--

I LIKE it.  I HATE it.  I LIKE it.  I HATE it.  I LIKE it.
I HATE it.  I LIKE..  EMOTIONS are SWEEPING over me!!
X-Newsreader: Gnus v5.6.42/Emacs 19.34

|> writes
|> >12.19 I'm re-prompting the user if scanf fails, but sometimes it seems to go
|> >into an infinite loop.
|> Of course because it leaves the problem in the input buffer until you
|> remove the relevant character.
|> >
|> >12.26 Will fflush(stdin) flush unread characters from the standard input
|> >stream?
|>
|> No.  Try
|> while(getchar() != '\n');
|> Which should read up to an including the carriage return.

And goes into an infinite loop if there isn't one before the next EOF or
read error.

--
Andreas Schwab                                      "And now for something


--

Sorry I am so used to using getchar() in systems where there must be a
CR because it is reading the keyboard that I tend to forget that
redirection might mean your data was coming from somewhere else:)

Francis Glassborow      Chair of Association of C & C++ Users
64 Southfield Rd
Oxford OX4 1PA          +44(0)1865 246490
All opinions are mine and do not represent those of any organisation
--