fread can not read particular data

[Meenakshi Matai]

I am trying to read data from a .dat file using fread.

This is how my syntax looks:
temp = fread(indata, sizeof(short int), 1, datafile);

I looked into the data file in Hex format and saw that everytime fread
finds the data "1A" it returns a non-zero value.

I tried with another .dat file and the same thing happens.
I went in and manually changed the contents of the .dat file.
Everywhere I found a "1A" I changed it to "1B" ("1C", "1D", "0D") and
it works just fine.
Anything but "1A" works fine.

Could you please suggest why this would be happening.

Thanks a lot in advance,
Meenakshi Matai.

[Keith Thompson]

mm****@signalog ic.com (Meenakshi Matai) writes:

I am trying to read data from a .dat file using fread.

This is how my syntax looks:
temp = fread(indata, sizeof(short int), 1, datafile);

I looked into the data file in Hex format and saw that everytime fread
finds the data "1A" it returns a non-zero value.

fread() returns the number of items read; if the call above succeeds,
it should return a non-zero value, specifically 1. I'm guessing you
meant that it returns zero.

Take a look at your call to fopen(). Did you open the file in binary
mode?

<speculation>
You're running on an MS-DOS or Windows system, and you opened the file
in text mode. The system uses an ASCII control-Z character (0x1A) as
an EOF marker for text files. You may also find that any occurrences
of "\r\n" (0X0D, 0x0A) are mapped to a single "\n" (0x0a). Opening
the file with
datafile = fopen("whatever .dat", "rb");
should fix the problem.
</speculation>

Posting a small, complete, compilable program that illustrates the
problem would have saved me the effort of using my uncanny
clairvoyance to figure out what's really causing the problem.

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Barry Schwarz]

On 23 Jun 2004 17:57:54 -0700, mm****@signalog ic.com (Meenakshi Matai)
wrote:

I am trying to read data from a .dat file using fread.

This is how my syntax looks:
temp = fread(indata, sizeof(short int), 1, datafile);
Is indata an array or pointer? If it is a short as implied, then you
should use &indata.

I looked into the data file in Hex format and saw that everytime fread
finds the data "1A" it returns a non-zero value.

I tried with another .dat file and the same thing happens.
I went in and manually changed the contents of the .dat file.
Everywhere I found a "1A" I changed it to "1B" ("1C", "1D", "0D") and
it works just fine.
Anything but "1A" works fine.

Could you please suggest why this would be happening.

Thanks a lot in advance,
Meenakshi Matai.

<<Remove the del for email>>

[Darrell Grainger]

On Wed, 23 Jun 2004, Meenakshi Matai wrote:

I am trying to read data from a .dat file using fread.

This is how my syntax looks:
temp = fread(indata, sizeof(short int), 1, datafile);
Insufficient information. Whenever you post a code snippet, give the data
types and how they were initialized. This posting is missing the
following:

1) what is the data type of indata?
2) how was indata initialized?
3) what is the data type of datafile?
4) how was datafile initialized?

I can only guess that this is what you have:

#include <stdlib.h>

short int *indata; /* answers #1 */
FILE *datafile; /* answers #3 */

indata = malloc(sizeof(s hort int)); /* answers #2 */
if(indata == NULL) exit(EXIT_FAILU RE);

datafile = fopen("filename .dat", "r"); /* answers #4 */
if(datafile == NULL) exit(EXIT_FAILU RE);

fread(indata, sizeof(short int), 1, datafile);
I looked into the data file in Hex format and saw that everytime fread
finds the data "1A" it returns a non-zero value.

I tried with another .dat file and the same thing happens.
I went in and manually changed the contents of the .dat file.
Everywhere I found a "1A" I changed it to "1B" ("1C", "1D", "0D") and
it works just fine.
Anything but "1A" works fine.

Could you please suggest why this would be happening.

The binary value 0x1A just happens to be the ASCII value CTRL-Z. On
MSDOS/Windows systems, CTRL-Z is the EOF for text files.

Problem: you have opened a binary file in text mode.
Solution: open the binary file in binary mode.

--
Send e-mail to: darrell at cs dot toronto dot edu
Don't send e-mail to vi************@ whitehouse.gov

[Meenakshi Matai]

Keith Thompson <ks***@mib.or g> wrote in message news:<ln******* *****@nuthaus.m ib.org>...

mm****@signalog ic.com (Meenakshi Matai) writes:

I am trying to read data from a .dat file using fread.

This is how my syntax looks:
temp = fread(indata, sizeof(short int), 1, datafile);

I looked into the data file in Hex format and saw that everytime fread
finds the data "1A" it returns a non-zero value.

fread() returns the number of items read; if the call above succeeds,
it should return a non-zero value, specifically 1. I'm guessing you
meant that it returns zero.

Take a look at your call to fopen(). Did you open the file in binary
mode?

<speculation>
You're running on an MS-DOS or Windows system, and you opened the file
in text mode. The system uses an ASCII control-Z character (0x1A) as
an EOF marker for text files. You may also find that any occurrences
of "\r\n" (0X0D, 0x0A) are mapped to a single "\n" (0x0a). Opening
the file with
datafile = fopen("whatever .dat", "rb");
should fix the problem.
</speculation>

Posting a small, complete, compilable program that illustrates the
problem would have saved me the effort of using my uncanny
clairvoyance to figure out what's really causing the problem.

OK.
Thanks for your help,
Meenakshi.