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From: ericblake AT comcast DOT net (Eric Blake)
To: Mikael <mindcooler AT gmail DOT com>, cygwin AT cygwin DOT com
Subject: Re: Why does stat fail for some files?
Date: Thu, 15 Sep 2005 20:02:13 +0000
Message-Id: <091520052002.22143.4329D3450002AB180000567F22007614380A050E040D0C079D0A@comcast.net>

> Hello, I'm doing homework and I'm having some problems with stat() failing. 

It's called homework for a reason, but here are some hints:

> Consider the following C program:
> 
> #include <assert.h>
> #include <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> 
> #include <dirent.h>
> #include <sys/stat.h>
> #include <sys/types.h>
> 
> static void scan_directory(const char *);
> 
> int
> main(int argc, char **argv)
> {
>    if(argc == 1)
>    {
>       fprintf(stderr, "Usage: dirscan path\n");
> 
>       return EXIT_FAILURE;
>    }
> 
>    scan_directory(argv[1]);
> 
>    return EXIT_SUCCESS;
> }
> 
> static void
> scan_directory(const char *path)
> {
>    DIR *directory = NULL;
>    struct dirent *entry = NULL;
>    struct stat statbuf;
>    int return_value = 0;
> 
>    directory = opendir(path);
> 
>    if(!directory)
>    {
>       fprintf(stderr, "Directory %s could not be opened.\n", path);

fprintf can clobber errno...

>       fprintf(stderr, "Reason: %s\n", strerror(errno));

so you may be printing the wrong reason.

> 
>       /* Don't exit program, we may have been called recursively and
>          we want to scan what we can.                                */
>       return;
>    }
> 
>    while((entry = readdir(directory)))

You just ignored the possibility that readdir might set errno.

>    {
>       return_value = stat(entry->d_name, &statbuf);

Hmm - think relative vs. absolute pathname, then consider where
you invoked your command.

> 
>       if(return_value)
>          fprintf(stderr, "stat() failed for %s. Reason: %s\n",
>                    entry->d_name, strerror(errno));
>       else
>          printf("stat() called successfully on: %s\n", entry->d_name);
>    }
> 
>    return_value = closedir(directory);
> 
>    assert(!return_value); /* closedir() returns 0 on success */
> }
> 
> And this is what happens when I run it (first ls -al):
> $ ls -al /c/cygwin/home/mikael/coding/cygwin/c++/read_directory/
> total 773
> drwxrwxrwx+  2 mikael None      0 Sep 15 16:36 ./
> drwxrwxrwx+ 16 mikael None      0 May 20 22:53 ../
> -rwxrwxrwx   1 mikael None    273 Sep 15 16:36 Makefile*
> -rwxrwxrwx   1 mikael None    792 Aug 19  2004 read_directory.cpp*
> -rwxr-xr-x   1 mikael None 604746 Sep 15 16:36 read_directory.exe*
> -rw-r--r--   1 mikael None 129520 Sep 15 16:36 read_directory.o
> 
> $ ./dirscan.exe /c/cygwin/home/mikael/coding/cygwin/c++/read_directory/
> stat() called successfully on: .
> stat() called successfully on: ..
> stat() called successfully on: Makefile
> stat() failed for read_directory.cpp. Reason: No such file or directory
> stat() failed for read_directory.exe. Reason: No such file or directory
> stat() failed for read_directory.o. Reason: No such file or directory

As a side note, Windows has the annoying habit that when a file
is locked by another application, stat() won't get much information
about the file, but at least it won't fail.

--
Eric Blake



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