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287 lines
9.4 KiB
Plaintext
287 lines
9.4 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "READDIR" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" readdir
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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.SH NAME
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readdir, readdir_r \- read a directory
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.SH SYNOPSIS
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.LP
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\fB#include <dirent.h>
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.br
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.sp
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struct dirent *readdir(DIR *\fP\fIdirp\fP\fB);
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.br
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\fP
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.LP
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\fBint readdir_r(DIR *restrict\fP \fIdirp\fP\fB, struct dirent *restrict\fP
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\fIentry\fP\fB,
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.br
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\ \ \ \ \ \ struct dirent **restrict\fP \fIresult\fP\fB); \fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The type \fBDIR\fP, which is defined in the \fI<dirent.h>\fP header,
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represents
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a \fIdirectory stream\fP, which is an ordered sequence of all the
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directory entries in a particular directory. Directory entries
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represent files; files may be removed from a directory or added to
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a directory asynchronously to the operation of
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\fIreaddir\fP().
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.LP
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The \fIreaddir\fP() function shall return a pointer to a structure
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representing the directory entry at the current position in
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the directory stream specified by the argument \fIdirp\fP, and position
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the directory stream at the next entry. It shall return a
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null pointer upon reaching the end of the directory stream. The structure
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\fBdirent\fP defined in the \fI<dirent.h>\fP header describes a directory
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entry.
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.LP
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The \fIreaddir\fP() function shall not return directory entries containing
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empty names. If entries for dot or dot-dot exist,
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one entry shall be returned for dot and one entry shall be returned
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for dot-dot; otherwise, they shall not be returned.
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.LP
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The pointer returned by \fIreaddir\fP() points to data which may be
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overwritten by another call to \fIreaddir\fP() on the same
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directory stream. This data is not overwritten by another call to
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\fIreaddir\fP() on a different directory stream.
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.LP
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If a file is removed from or added to the directory after the most
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recent call to \fIopendir\fP() or \fIrewinddir\fP(), whether a
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subsequent call to \fIreaddir\fP() returns an entry for that file
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is unspecified.
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.LP
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The \fIreaddir\fP() function may buffer several directory entries
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per actual read operation; \fIreaddir\fP() shall mark for
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update the \fIst_atime\fP field of the directory each time the directory
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is actually read.
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.LP
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After a call to \fIfork\fP(), either the parent or child (but not
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both) may continue
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processing the directory stream using \fIreaddir\fP(), \fIrewinddir\fP(),
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\ or \fIseekdir\fP(). If both the
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parent and child processes use these functions, the result is undefined.
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.LP
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If the entry names a symbolic link, the value of the \fId_ino\fP member
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is unspecified.
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.LP
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The \fIreaddir\fP() function need not be reentrant. A function that
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is not required to be reentrant is not required to be
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thread-safe.
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.LP
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The \fIreaddir_r\fP() function shall initialize the \fBdirent\fP structure
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referenced by \fIentry\fP to represent the directory
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entry at the current position in the directory stream referred to
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by \fIdirp\fP, store a pointer to this structure at the location
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referenced by \fIresult\fP, and position the directory stream at the
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next entry.
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.LP
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The storage pointed to by \fIentry\fP shall be large enough for a
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\fBdirent\fP with an array of \fBchar\fP \fId_name\fP
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members containing at least {NAME_MAX}+1 elements.
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.LP
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Upon successful return, the pointer returned at *\fIresult\fP shall
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have the same value as the argument \fIentry\fP. Upon
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reaching the end of the directory stream, this pointer shall have
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the value NULL.
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.LP
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The \fIreaddir_r\fP() function shall not return directory entries
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containing empty names.
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.LP
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If a file is removed from or added to the directory after the most
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recent call to \fIopendir\fP() or \fIrewinddir\fP(), whether a
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subsequent call to \fIreaddir_r\fP() returns an entry for that file
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is unspecified.
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.LP
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The \fIreaddir_r\fP() function may buffer several directory entries
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per actual read operation; the \fIreaddir_r\fP() function
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shall mark for update the \fIst_atime\fP field of the directory each
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time the directory is actually read.
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.LP
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Applications wishing to check for error situations should set \fIerrno\fP
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to 0 before calling \fIreaddir\fP(). If \fIerrno\fP
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is set to non-zero on return, an error occurred.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIreaddir\fP() shall return a pointer
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to an object of type \fBstruct dirent\fP. When an error is
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encountered, a null pointer shall be returned and \fIerrno\fP shall
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be set to indicate the error. When the end of the directory is
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encountered, a null pointer shall be returned and \fIerrno\fP is not
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changed.
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.LP
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If successful, the \fIreaddir_r\fP() function shall return zero; otherwise,
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an error number shall be returned to indicate the
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error.
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.SH ERRORS
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.LP
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The \fIreaddir\fP() function shall fail if:
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.TP 7
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.B EOVERFLOW
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One of the values in the structure to be returned cannot be represented
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correctly.
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.sp
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.LP
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The \fIreaddir\fP() function may fail if:
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.TP 7
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.B EBADF
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The \fIdirp\fP argument does not refer to an open directory stream.
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.TP 7
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.B ENOENT
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The current position of the directory stream is invalid.
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.sp
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.LP
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The \fIreaddir_r\fP() function may fail if:
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.TP 7
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.B EBADF
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The \fIdirp\fP argument does not refer to an open directory stream.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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The following sample program searches the current directory for each
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of the arguments supplied on the command line.
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.sp
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.RS
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.nf
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\fB#include <dirent.h>
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#include <errno.h>
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#include <stdio.h>
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#include <string.h>
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.sp
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static void lookup(const char *arg)
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{
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DIR *dirp;
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struct dirent *dp;
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.sp
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if ((dirp = opendir(".")) == NULL) {
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perror("couldn't open '.'");
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return;
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}
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.sp
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do {
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errno = 0;
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if ((dp = readdir(dirp)) != NULL) {
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if (strcmp(dp->d_name, arg) != 0)
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continue;
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.sp
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(void) printf("found %s\\n", arg);
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(void) closedir(dirp);
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return;
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.sp
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}
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} while (dp != NULL);
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.sp
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if (errno != 0)
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perror("error reading directory");
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else
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(void) printf("failed to find %s\\n", arg);
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(void) closedir(dirp);
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return;
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}
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.sp
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int main(int argc, char *argv[])
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{
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int i;
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for (i = 1; i < argc; i++)
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lookup(arvg[i]);
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return (0);
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}
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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The \fIreaddir\fP() function should be used in conjunction with \fIopendir\fP(),
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\fIclosedir\fP(), and \fIrewinddir\fP() to
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examine the contents of the directory.
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.LP
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The \fIreaddir_r\fP() function is thread-safe and shall return values
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in a user-supplied buffer instead of possibly using a
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static data area that may be overwritten by each call.
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.SH RATIONALE
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.LP
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The returned value of \fIreaddir\fP() merely \fIrepresents\fP a directory
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entry. No equivalence should be inferred.
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.LP
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Historical implementations of \fIreaddir\fP() obtain multiple directory
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entries on a single read operation, which permits
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subsequent \fIreaddir\fP() operations to operate from the buffered
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information. Any wording that required each successful
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\fIreaddir\fP() operation to mark the directory \fIst_atime\fP field
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for update would disallow such historical
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performance-oriented implementations.
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.LP
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Since \fIreaddir\fP() returns NULL when it detects an error and when
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the end of the directory is encountered, an application
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that needs to tell the difference must set \fIerrno\fP to zero before
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the call and check it if NULL is returned. Since the
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function must not change \fIerrno\fP in the second case and must set
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it to a non-zero value in the first case, a zero \fIerrno\fP
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after a call returning NULL indicates end-of-directory; otherwise,
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an error.
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.LP
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Routines to deal with this problem more directly were proposed:
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.sp
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.RS
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.nf
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\fBint derror (\fP\fIdirp\fP\fB)
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DIR *\fP\fIdirp\fP\fB;
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.sp
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void clearderr (\fP\fIdirp\fP\fB)
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DIR *\fP\fIdirp\fP\fB;
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\fP
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.fi
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.RE
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.LP
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The first would indicate whether an error had occurred, and the second
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would clear the error indication. The simpler method
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involving \fIerrno\fP was adopted instead by requiring that \fIreaddir\fP()
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not change \fIerrno\fP when end-of-directory is
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encountered.
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.LP
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An error or signal indicating that a directory has changed while open
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was considered but rejected.
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.LP
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The thread-safe version of the directory reading function returns
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values in a user-supplied buffer instead of possibly using a
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static data area that may be overwritten by each call. Either the
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{NAME_MAX} compile-time constant or the corresponding \fIpathconf\fP()
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option can be used to determine the maximum sizes of returned pathnames.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIclosedir\fP(), \fIlstat\fP(), \fIopendir\fP(), \fIrewinddir\fP(),
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\fIsymlink\fP(),
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the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<dirent.h>\fP,
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\fI<sys/types.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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