Originální popis anglicky:
readlink - read the contents of a symbolic link
Návod, kniha: POSIX Programmer's Manual
#include <unistd.h>
ssize_t readlink(const char *restrict
path, char
*restrict buf,
size_t
bufsize);
The
readlink() function shall place the contents of the symbolic link
referred to by
path in the buffer
buf which has size
bufsize. If the number of bytes in the symbolic link is less than
bufsize, the contents of the remainder of
buf are unspecified.
If the
buf argument is not large enough to contain the link content,
the first
bufsize bytes shall be placed in
buf.
If the value of
bufsize is greater than {SSIZE_MAX}, the result is
implementation-defined.
Upon successful completion,
readlink() shall return the count of bytes
placed in the buffer. Otherwise, it shall return a value of -1, leave the
buffer unchanged, and set
errno to indicate the error.
The
readlink() function shall fail if:
- EACCES
- Search permission is denied for a component of the path
prefix of path.
- EINVAL
- The path argument names a file that is not a
symbolic link.
- EIO
- An I/O error occurred while reading from the file
system.
- ELOOP
- A loop exists in symbolic links encountered during
resolution of the path argument.
- ENAMETOOLONG
- The length of the path argument exceeds {PATH_MAX}
or a pathname component is longer than {NAME_MAX}.
- ENOENT
- A component of path does not name an existing file
or path is an empty string.
- ENOTDIR
- A component of the path prefix is not a directory.
The
readlink() function may fail if:
- EACCES
- Read permission is denied for the directory.
- ELOOP
- More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
- ENAMETOOLONG
- As a result of encountering a symbolic link in resolution
of the path argument, the length of the substituted pathname string
exceeded {PATH_MAX}.
The following sections are informative.
The following example shows how to read the name of a symbolic link named
/modules/pass1.
#include <unistd.h>
char buf[1024];
ssizet_t len;
...
if ((len = readlink("/modules/pass1", buf, sizeof(buf)-1)) != -1)
buf[len] = '\0';
Conforming applications should not assume that the returned contents of the
symbolic link are null-terminated.
Since IEEE Std 1003.1-2001 does not require any association of
file times with symbolic links, there is no requirement that file times be
updated by
readlink(). The type associated with
bufsiz is a
size_t in order to be consistent with both the ISO C standard
and the definition of
read(). The behavior specified for
readlink() when
bufsiz is zero represents historical practice.
For this case, the standard developers considered a change whereby
readlink() would return the number of non-null bytes contained in the
symbolic link with the buffer
buf remaining unchanged; however, since
the
stat structure member
st_size value can be used to determine
the size of buffer necessary to contain the contents of the symbolic link as
returned by
readlink(), this proposal was rejected, and the historical
practice retained.
None.
lstat() ,
stat() ,
symlink() , the Base Definitions volume
of IEEE Std 1003.1-2001,
<unistd.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
