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<H2><A NAME="s11">11. Third Example: Fortune</A></H2>
<P>This example requires some knowledge of C programming. The majority
of UNIX/Linux software is written in C, and learning at least a little
bit of C would certainly be an asset for anyone serious about software
installation.
<P>The notorious <EM>fortune</EM> program displays up a humorous saying, a
"fortune cookie", every time Linux boots up. Unfortunately (pun intended),
attempting to build fortune on a Red Hat distribution with a 2.0.30
kernel generates fatal errors.
<P>
<BLOCKQUOTE><CODE>
<PRE>
~/fortune# make all
gcc -O2 -Wall -fomit-frame-pointer -pipe -c fortune.c -o
fortune.o
fortune.c: In function `add_dir':
fortune.c:551: structure has no member named `d_namlen'
fortune.c:553: structure has no member named `d_namlen'
make[1]: *** [fortune.o] Error 1
make[1]: Leaving directory `/home/thegrendel/for/fortune/fortune'
make: *** [fortune-bin] Error 2
</PRE>
</CODE></BLOCKQUOTE>
<P>
<P>
<P>
<P>Looking at <CODE>fortune.c</CODE>, the pertinent lines are these.
<P>
<BLOCKQUOTE><CODE>
<PRE>
if (dirent->d_namlen == 0)
continue;
name = copy(dirent->d_name, dirent->d_namlen);
</PRE>
</CODE></BLOCKQUOTE>
<P>We need to find the structure <CODE>dirent</CODE>, but it is not declared in
the <EM>fortune.c</EM> file, nor does a <B>grep dirent</B> show it in
any of the other source files. However, at the top of
<EM>fortune.c</EM>, there is the following line.
<P>
<BLOCKQUOTE><CODE>
<PRE>
#include <dirent.h>
</PRE>
</CODE></BLOCKQUOTE>
<P>This appears to be a system library include file, therefore, the logical
place to look for <EM>dirent.h</EM> is in <EM>/usr/include</EM>.
Indeed, there does exist a <EM>dirent.h</EM> file in
<EM>/usr/include</EM>, but that file does not contain the declaration of
the <CODE>dirent</CODE> structure. There is, however, a reference to
another <EM>dirent.h</EM> file.
<P>
<BLOCKQUOTE><CODE>
<PRE>
#include <linux/dirent.h>
</PRE>
</CODE></BLOCKQUOTE>
<P>
<P>At last, going to <EM>/usr/include/linux/dirent.h</EM>, we find the
structure declaration we need.
<P>
<BLOCKQUOTE><CODE>
<PRE>
struct dirent {
long d_ino;
__kernel_off_t d_off;
unsigned short d_reclen;
char d_name[256]; /* We must not include
limits.h! */
};
</PRE>
</CODE></BLOCKQUOTE>
<P>Sure enough, the structure declaration contains no <EM>d_namelen</EM>,
but there are a couple of "candidates" for its equivalent. The most
likely of these is <EM>d_reclen</EM>, since this structure member
probably represents the length of something and it is a short integer.
The other possibility, <EM>d_ino</EM>, could be an inode number, judging
by its name and type. As a matter of fact, we are probably dealing with
a "directory entry" structure, and these elements represent attributes
of a file, its name, inode, and length (in blocks). This would seem to
validate our guess.
<P>Let us edit the file <CODE>fortune.c</CODE>, and change the two
<EM>d_namelen</EM> references in lines 551 and 553 to <EM>d_reclen</EM>.
Try a <EM>make all</EM> again. <B>Success.</B> It builds without
errors. We can now get our "cheap thrills" from fortune.
<P>
<P>
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