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Top Forums UNIX for Dummies Questions & Answers Unix directory system calls question Post 302531106 by Izzy123 on Thursday 16th of June 2011 02:08:24 AM
Old 06-16-2011
Unix directory system calls question

I'm currently studying for my exam, and is practicing with sample exam questions.

However there is a question asking "Name THREE UNIX Directory system calls" and the answer given is "opendir, closedir and readdir", however the next question ask "Why is a write directory system call not included in the above list?"

I'm not sure about the answer to this question so can anyone help me out?
 

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DIRECTORY(3)						     Library Functions Manual						      DIRECTORY(3)

NAME
opendir, readdir, telldir, seekdir, rewinddir, closedir - directory operations SYNOPSIS
#include <sys/types.h> #include <sys/dir.h> DIR *opendir(filename) char *filename; struct direct *readdir(dirp) DIR *dirp; long telldir(dirp) DIR *dirp; seekdir(dirp, loc) DIR *dirp; long loc; rewinddir(dirp) DIR *dirp; closedir(dirp) DIR *dirp; DESCRIPTION
Opendir opens the directory named by filename and associates a directory stream with it. Opendir returns a pointer to be used to identify the directory stream in subsequent operations. The pointer NULL is returned if filename cannot be accessed, or if it cannot malloc(3) enough memory to hold the whole thing. Readdir returns a pointer to the next directory entry. It returns NULL upon reaching the end of the directory or detecting an invalid seekdir operation. Telldir returns the current location associated with the named directory stream. Seekdir sets the position of the next readdir operation on the directory stream. The new position reverts to the one associated with the directory stream when the telldir operation was performed. Values returned by telldir are good only for the lifetime of the DIR pointer from which they are derived. If the directory is closed and then reopened, the telldir value may be invalidated due to undetected direc- tory compaction. It is safe to use a previous telldir value immediately after a call to opendir and before any calls to readdir. Rewinddir resets the position of the named directory stream to the beginning of the directory. Closedir closes the named directory stream and frees the structure associated with the DIR pointer. Sample code which searchs a directory for entry ``name'' is: len = strlen(name); dirp = opendir("."); for (dp = readdir(dirp); dp != NULL; dp = readdir(dirp)) if (dp->d_namlen == len && !strcmp(dp->d_name, name)) { closedir(dirp); return FOUND; } closedir(dirp); return NOT_FOUND; SEE ALSO
open(2), close(2), read(2), lseek(2), dir(5) 4.2 Berkeley Distribution September 24, 1985 DIRECTORY(3)
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