Thread: Problem with read().(from K&R)

  1. #1
    Registered User
    Join Date
    May 2008

    Problem with read().(from K&R)

    I am in the learning phase of c. I am reading K & R and trying to execute one of the program "listing directories".
    #include "cDirent.h"
    #include "syscall.h"
    #ifndef DIRSIZ
    #define DIRSIZ 14
    Dir *copendir(char *dirname){
      int fd;
      struct stat stbuf;
      Dir *dp;
      if((fd=open(dirname,O_RDONLY,0)) == -1 || fstat(fd,&stbuf) == -1 || (stbuf.st_mode & S_IFMT) != S_IFDIR || (dp = (Dir *) malloc (sizeof(Dir))) == NULL)
        return NULL;
      return dp;
    void cclosedir(Dir *d){
    Dirent *creaddir(Dir *dp){
      struct direct dirbuf;
      static Dirent d;
      int c;
      while((c=read(dp->fd,(char *) &dirbuf,sizeof(dirbuf))) == sizeof(dirbuf)){
        if(dirbuf.d_ino == 0)
        d.inod = dirbuf.d_ino;
        return &d;
      return NULL;
    I am calling these function from other program. First I opened the directory and it went fine. But when i use the creaddir function,its giving me NULL, because the system call read is giving -1. I have debugged the program using gdb, and found that fd passed is 6, which i got from the copendir function.
    Can someone please help regarding this?
    Thank you.

  2. #2
    Registered User
    Join Date
    Sep 2007
    When a system call returns error, you should check errno; in this case I suspect that read() is setting errno to EISDIR. That is, your read() probably refuses to read from a directory. POSIX provides opendir() and readdir() for reading directories. I suppose that using those functions to implement your own versions would be rather, boring, though!

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