Regarding checking for file or directory - c

Question

I have a very simple program here, but it seems to be returning
a "true" value to the query S_ISDIR() even when the directory
entry is not a directory. Can any one pleeas help me. I am using QNX Neurtion RTOS
#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <errno.h>
int main(int argc, char *argv[]) {
DIR *dir;
struct dirent *entry;
struct stat eStat;
char *root;
int i;
root = argv[1];
while((entry = readdir(dir)) != NULL) {
lstat(entry->d_name, &eStat);
if(S_ISDIR(eStat.st_mode))
printf("found directory %s\n", entry->d_name);
else
printf("not a dir\n");
}
return 0;
}
sample output:
found directory .
found directory ..
found directory NCURSES-Programming-HOWTO-html.tar.gz
found directory ncurses_programs
found directory ncurses.html
Following information may be helpful.
lstat for file is failing with errno set to 2. I am not sure why, can any one know this.

Answer 1

Just a guess; since you're not checking for an error after your lstat call, the eStat buffer could be containing the result of the last successful call. Try checking if lstat returns -1.
readdir() on Linux is fundamentally different, so I can't fully test on my system. See the sample programs at link text and link text. Modifying the lstat sample code, this seems to work for me:
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
int main( int argc, char **argv )
{
int ecode = 0;
int n;
struct stat sbuf;
for( n = 1; n < argc; ++n ) {
if( lstat( argv[n], &sbuf ) == -1 ) {
perror( argv[n] );
ecode++;
} else if( S_ISDIR( sbuf.st_mode ) ) {
printf( "%s is a dir\n", argv[n] );
} else {
printf( "%s is not a dir\n", argv[n] );
}
}
}
I don't know if that helps any. Note that the readdir() sample code uses opendir() as schot suggested. But I can't explain why your readdir() seems to work regardless.

Answer 2

My compiler says: "warning: 'dir' is used uninitialized in this function" You may want to add dir = opendir(root); after you initialize root. And don't forget to add some error checking.
I doubt this causes your problem, jcomeau_ictx is probably right. If lstat returns -1 it sets errno to a value that signifies the type of error. Look at its man page and the man page for strerror

Answer 3

Even though this question was asked long time ago, and I found it because this quesion. but the answers here didn't really solve the problem, so I decided to post the answer which I wrote on another post, such that if anyone had the same problem and used google to find this page, there is a clear answer.
The real reason of S_ISDIR not working as expected is dp->d_name contains only the name of the file, you need to pass the full path of the file to lstat().