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<p class="MsoNormal">void PrintFileNames(char *dir)</p>
<p class="MsoNormal">{</p>
<p class="MsoNormal"> FTS *filetree = NULL;</p>
<p class="MsoNormal"> FTSENT *file = NULL;</p>
<p class="MsoNormal"> FTSENT *child = NULL;</p>
<p class="MsoNormal"> char *path[] = { dir, NULL };</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> filetree = fts_open(path, FTS_PHYSICAL, NULL);</p>
<p class="MsoNormal"> if (filetree == NULL)</p>
<p class="MsoNormal"> warn("fts_open failed");</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> else</p>
<p class="MsoNormal"> {</p>
<p class="MsoNormal"> while ((file = fts_read(filetree)) != NULL)</p>
<p class="MsoNormal"> {</p>
<p class="MsoNormal"> child = fts_children(filetree, 0);</p>
<p class="MsoNormal"> warn("%d", errno);</p>
<p class="MsoNormal"> if (child == NULL)</p>
<p class="MsoNormal"> warn("fts_children");</p>
<p class="MsoNormal"> printf("%s\n", child->fts_name);</p>
<p class="MsoNormal"> }</p>
<p class="MsoNormal"> }</p>
<p class="MsoNormal"> if (errno != 0)</p>
<p class="MsoNormal"> warn("fts_read failed");</p>
<p class="MsoNormal"> if (fts_close(filetree) < 0)</p>
<p class="MsoNormal"> warn("fts_close");</p>
<p class="MsoNormal">}</p>
<p class="MsoNormal">int main(int argc, char *argv[])</p>
<p class="MsoNormal">{</p>
<p class="MsoNormal"> if (argc == 1)</p>
<p class="MsoNormal"> PrintFileNames(".");</p>
<p class="MsoNormal">}</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hello,</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here is your code. I changed all the <span style="font-size:12.0pt;color:black">
ErrorMessage functions to warn, so that I can output the error message more easily.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">And this is the quote to fts(3):<o:p></o:p></span></p>
<p class="MsoNormal">if the FTSENT structure most recently returned by fts_read() is not a directory being visited in pre-order, or the directory does not contain any files, fts_children() returns NULL and sets errno to zero.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">First time, you read dir-“.” in the while, and then you call fts_children. This time of loop works fine. var child has the information in dir-“.”.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Second time, fts_read begins to read into “.” And the first file it reads happens to be a regular file. This causes var child to be NULL and set errno to 0.</p>
<p class="MsoNormal">Then you call printf child->fts_name which references a NULL pointer. Here is the point that seg-fault occurs.</p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">I don’t think “fts_children: Undefined error: 0.” Is an error message. It just tells the errno is 0 and 0 is not an error…</span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div style="mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal" style="border:none;padding:0in"><b>From: </b><a href="mailto:mseaton@stevens.edu">Marlon Seaton</a><br>
<b>Sent: </b>Tuesday, October 8, 2019 12:11 PM<br>
<b>To: </b><a href="mailto:jschauma@stevens.edu">Jan Schaumann</a>; <a href="mailto:cs631apue@lists.stevens.edu">
cs631apue@lists.stevens.edu</a><br>
<b>Subject: </b>Re: [cs631apue] About FTS</p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Hello,<o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">I am trying to use fts to traverse through the current directory without recursion and i either get a segfault of the following error when I call fts_children()<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">fts_children: Undefined error: 0.<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Here's my code snippet below:<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">main<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">{<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> if(argc == 1)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> PrintFileNames(".");<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">}<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">void PrintFileNames(char* dir )<o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">{<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> FTS *filetree = NULL;<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> FTSENT *file = NULL;<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> FTSENT *child = NULL;<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> char *path[] = {dir, NULL};<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> filetree = fts_open(path, FTS_PHYSICAL, &compare);<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> if(filetree == NULL)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> ErrorMessage("fts_open failed");<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> else<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> {<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> while((file = fts_read(filetree)) != NULL)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> {<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> child = fts_children(filetree, 0);<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> if(child == NULL)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> ErrorMessage("fts_children");<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> printf("%s\n",child->fts_name);<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> }<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> }<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> if(errno != 0)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> ErrorMessage("fts_read failed");<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> if( fts_close(filetree) < 0)<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"> ErrorMessage("fts_close");<o:p></o:p></span></p>
</div>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">}<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Can anyone shed some light on what's going on?<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><span style="font-size:12.0pt;color:black">Thanks.<o:p></o:p></span></p>
</div>
<p class="MsoNormal"><img border="0" width="463" height="2" style="width:4.8194in;height:.0208in" id="Horizontal_x0020_Line_x0020_1" src="cid:image002.png@01D57E21.49EA73A0"><o:p></o:p></p>
<div id="divRplyFwdMsg">
<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> cs631apue-bounces@lists.stevens.edu <cs631apue-bounces@lists.stevens.edu> on behalf of Jan Schaumann <jschauma@stevens.edu><br>
<b>Sent:</b> Sunday, October 6, 2019 4:35 PM<br>
<b>To:</b> cs631apue@lists.stevens.edu <cs631apue@lists.stevens.edu><br>
<b>Subject:</b> Re: [cs631apue] About FTS</span> <o:p></o:p></p>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<p class="MsoNormal">Yuxi Wang <ywang286@stevens.edu> wrote:<br>
<br>
> 1.To use these fields to reference any files represented by<br>
> other FTSENT structures will require that the path buffer be modified<br>
> using the information contained in that FTSENT structure's fts_pathlen<br>
> field. Any such modifications should be undone before further calls to<br>
> fts_read() are attempted. The fts_name field is always NUL-terminated.<br>
<br>
I'm honestly struggling to come up with a useful<br>
example, but the point is that you cannot manipulate<br>
the buffers (e.g., via strcat(3) etc.) in e.g., your<br>
comparison function, nor can you rely on the buffer to<br>
be NULL terminated for a previously returned element.<br>
<br>
That means that you can't keep a pointer to the<br>
element returned and subsequently call e.g. strlen(3)<br>
on _that_ element's fts_path field.<br>
<br>
Let's say you want to write a program that will print<br>
the path within the parent directory:<br>
<br>
$ pwd<br>
/tmp<br>
$ ls<br>
file<br>
$ printParentPath file<br>
tmp/file<br>
$ printParentPath /var/tmp/subdir/file<br>
subdir/file<br>
<br>
This might require you to keep track of the parent<br>
struct. You might try to<br>
<br>
- get strlen of current entry accpath, n<br>
- get strlen of parent entry accpath, m<br>
- malloc a buffer of size n + 1 + m<br>
- sprintf parent, '/', current to buffer<br>
<br>
But the parent entry's accpath may not be<br>
NULL-terminated, thus strlen(3) giving you a bogus<br>
result.<br>
<br>
> 2.What does the fts_accpath represent for? I tracked<br>
> the FTS structure and found it always equal<br>
> fts_name.<br>
<br>
fts_accpath will be different depending on whether<br>
you've specified FTS_NOCHDIR or not. With<br>
FTS_NOCHDIR, fts_accpath will look like fts_path,<br>
without, fts_accpath will look like fts_name.<br>
<br>
I haven't verified, but I could imagine that results<br>
will also differ based on whether you're following<br>
symlinks and the hierarchy includes symlinks to<br>
directories whereby directory traversal may encounter<br>
the same subdir via multiple paths.<br>
<br>
-Jan<br>
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<a href="https://lists.stevens.edu/mailman/listinfo/cs631apue">https://lists.stevens.edu/mailman/listinfo/cs631apue</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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