|  | return value? | | |
| | | Bill Cunningham |  |
|  Posted: Tue Aug 26, 2008 11:17 pm Post subject: return value? |  |
I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine but the thing is I always check for fgetc's RV
and it's always -1. If the program doesn't work right I get -1. Is -1 always
an error code and doesn't it always mean failure?
Bill |
| |
| | | Richard Heathfield | |
| | Posted: Tue Aug 26, 2008 11:23 pm Post subject: Re: return value? | |
Bill Cunningham said:
| Quote: | I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine but the thing is I always check for fgetc's
RV and it's always -1. If the program doesn't work right I get -1. Is -1
always an error code and doesn't it always mean failure?
|
Code, please.
--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999 |
| |
| | | Gordon Burditt | |
| | Posted: Tue Aug 26, 2008 11:41 pm Post subject: Re: return value? | |
| Quote: | I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine
|
Did you look at the copied files? Are they filled with the correct
characters or -1? If they are filled with correct characters, then
fgetc() is *NOT* always returning -1.
Read the documentation on fgetc() that should have come with your compiler.
| Quote: | but the thing is I always check for fgetc's RV
and it's always -1.
|
EOF probably has the value of -1 on your system.
| Quote: | If the program doesn't work right I get -1. Is -1 always
an error code and doesn't it always mean failure?
|
I don't consider EOF to be an error code. You can test whether an
error occurred after getting back EOF as a return value by using
ferror(). If you keep reading a file, you'll usually get EOF (real
end-of-file) eventually (with exceptions for non-ordinary files
like /dev/zero or /dev/random). Getting EOF in the wrong place
might indicate an error. |
| |
| | | Keith Thompson | |
| | Posted: Wed Aug 27, 2008 12:05 am Post subject: Re: return value? | |
"Bill Cunningham" <nospam@nspam.com> writes:
| Quote: | I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine but the thing is I always check for fgetc's RV
and it's always -1. If the program doesn't work right I get -1. Is -1 always
an error code and doesn't it always mean failure?
|
You should not have to ask this question. You should be able to
discover the answer without outside help.
Re-read <http://groups.google.com/group/comp.lang.c/msg/6da991ad26d30ed9>.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister" |
| |
| | | pete | |
| | Posted: Wed Aug 27, 2008 12:06 am Post subject: Re: return value? | |
Bill Cunningham wrote:
| Quote: | I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine but the thing is I always check for fgetc's RV
and it's always -1. If the program doesn't work right I get -1. Is -1 always
an error code and doesn't it always mean failure?
|
On some implementations, EOF is equal to (-1).
Your code should be checking to see
if the return value is equal to EOF.
--
pete |
| |
| | | Guest | |
| | Posted: Wed Aug 27, 2008 1:20 am Post subject: Re: return value? | |
On Aug 27, 4:17 am, "Bill Cunningham" <nos...@nspam.com> wrote:
| Quote: | I have been using fgetc and fputc with a while loop construct to copy
files. It seems to work fine but the thing is I always check for fgetc's RV
and it's always -1. If the program doesn't work right I get -1. Is -1 always
an error code and doesn't it always mean failure?
|
No. It's EOF (<stdio.h> and others). On your implementation, EOF
happends to be -1. |
| |
| | | Bill Cunningham | |
| | Posted: Wed Aug 27, 2008 4:58 pm Post subject: Re: return value? | |
"Richard Heathfield" <rjh@see.sig.invalid> wrote in message
news:tOSdnUjtRZsyNinV4p2dnAA@bt.com...
#include <stdio.h>
int main()
{
FILE *fr, *fw;
int i, a;
if ((fr = fopen("bs", "rb")) == NULL) {
puts("open error");
}
if ((fw = fopen("e", "w")) == NULL) {
puts("open error 2");
}
while ((i = fgetc(fr)) != EOF)
fputc(a, fw);
printf("%i\n", i);
fclose(fr);
fclose(fw);
} |
| |
| | | Bill Cunningham | |
| | Posted: Wed Aug 27, 2008 5:03 pm Post subject: Re: return value? | |
"pete" <pfiland@mindspring.com> wrote in message
news:5rudnbS8Wr0FKynVnZ2dnUVZ_rfinZ2d@earthlink.com...
| Quote: | On some implementations, EOF is equal to (-1).
Your code should be checking to see
if the return value is equal to EOF.
|
Sounds like everything is in order then. It's just that EOF which I'm
sure fgetc reached, has a value of -1. Now if there was an error, the return
value of fgetc wouldn't be -1 if I surmise correctly.
Bill |
| |
| | | Bill Cunningham | |
| | Posted: Wed Aug 27, 2008 5:08 pm Post subject: Re: return value? | |
| |  | |
"Gordon Burditt" <gordonb.xigrr@burditt.org> wrote in message
news:FJqdnVu_Av1HLSnVnZ2dnUVZ_g6dnZ2d@posted.internetamerica...
| Quote: |
Did you look at the copied files? Are they filled with the correct
characters or -1? If they are filled with correct characters, then
fgetc() is *NOT* always returning -1.
Read the documentation on fgetc() that should have come with your
compiler.
EOF probably has the value of -1 on your system.
I don't consider EOF to be an error code. You can test whether an
error occurred after getting back EOF as a return value by using
ferror(). If you keep reading a file, you'll usually get EOF (real
end-of-file) eventually (with exceptions for non-ordinary files
like /dev/zero or /dev/random). Getting EOF in the wrong place
might indicate an error.
|
No special device file are involved here. I didn't know EOF meant -1. I
just use the EOF macro. I always thought -1 meant error. I have copied a
file from binary format and written it like a text file so I don't know if
the characters are right or not. So I will try coping a text to text file.
Bill |
| |
| | | Richard Heathfield | |
| | Posted: Wed Aug 27, 2008 5:16 pm Post subject: Re: return value? | |
Bill Cunningham said:
<snip>
| Quote: | while ((i = fgetc(fr)) != EOF)
fputc(a, fw);
printf("%i\n", i);
|
So you keep copying characters until i gets the value EOF, and then you
stop, and print the value i has. At this point, it is *bound* to have the
value EOF, because for as long as it had any other value, it could never
reach this point in the code.
On your system, EOF happens to be -1, so -1 is what got printed.
--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999 |
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