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Old 03-13-2008, 12:44 PM   #1
thefountainhead100
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Unhappy Doubt in a simple basic C program....


Hi

I am new to C prog..

I just want to know what is the problem with the following code.

#define BUFSIZE 1024
int main(void)
{
char *s;
FILE *fp;
s = malloc (BUFSIZE);

fp = fopen("~/Documents/newtxt.txt", "rb");
fgets( s, BUFSIZE, fp);
printf("%s", s);
return 0;
}

I have a text file in ~/Documents names newtxt with a line of text in it. I just want to read it and print it on screen. It compiles OK but when i execute it gives "SEGEMENTATION FAULT: CORE DUMPED"

I also tried fgets(s,BUFSIZE-1,fp) above.. same result.

Your help is appreciated.
Thanks.
Ash
 
Old 03-13-2008, 01:00 PM   #2
osor
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You can’t pass the character ‘~’ as the home directory in your system calls. This only works if you have some sort of shell interpretation to handle your environment variables. You might have found this out if you bothered to check the return value of fopen().
 
Old 03-13-2008, 01:01 PM   #3
exscape
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Check if (!fp).
I'd bet that the ~ is the problem. Specify the full path and it should work.
 
Old 03-13-2008, 09:15 PM   #4
Dan04
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Quote:
Originally Posted by exscape View Post
Check if (!fp).
I'd bet that the ~ is the problem. Specify the full path and it should work.
Or use getenv("HOME").
 
Old 03-13-2008, 10:01 PM   #5
matthewg42
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Also, you should not assume char is one byte. Your malloc line should read:
Code:
s = malloc (BUFSIZE * sizeof(char));
And you should check that malloc worked too (check that s != NULL).
 
Old 03-13-2008, 10:21 PM   #6
osor
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Quote:
Originally Posted by matthewg42 View Post
Also, you should not assume char is one byte.
This is wrong. The C standard guarantees that
Code:
sizeof(char)
always evaluates to 1 (see §6.5.3.4.3). What one should not assume is that the number of bits in a char is 8.
 
Old 03-13-2008, 10:44 PM   #7
matthewg42
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Quote:
Originally Posted by osor View Post
This is wrong. The C standard guarantees that
Code:
sizeof(char)
always evaluates to 1 (see §6.5.3.4.3). What one should not assume is that the number of bits in a char is 8.
I didn't know that was in the standard. In that case you probably can assume it will be a byte.

If you're ultra-paranoid you might still want to check it since char could be set to something else using a macro, although I expect that would break lots of other stuff before you have to worry about it in your own code.
 
Old 03-14-2008, 09:02 AM   #8
simplicissimus
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source code

I would do it like this (formatting is last unfortunately after posting the message):

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

#define BUFSIZE 1024
int main(void)
{
char *s;
FILE *fp;
char filename[64];

s = malloc (BUFSIZE);
if (!s) {
printf ("malloc error\n");
return -1L;
}
sprintf (filename, "%s/Documents/newtxt.txt", getenv("HOME"));

fp = fopen (filename, "rb");
if (!fp) {
printf ("fopen error\n");
return -2L;
}
fgets (s, BUFSIZE, fp);
printf ("%s", s);
fclose (fp);
return 0L;
}


Hope this helps,
Regards,
SIMP

Linux Archive

Last edited by simplicissimus; 04-02-2008 at 04:28 AM.
 
Old 03-14-2008, 02:40 PM   #9
Tinkster
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Quote:
Originally Posted by simplicissimus View Post
I would do it like this (formatting is last unfortunately after posting the message):

You could edit your post and put CODE tags around it?
 
Old 03-15-2008, 01:01 AM   #10
thefountainhead100
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Thanks people. Problem solved. It was the '~'.
 
  


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