POSIX.2 defines a way to get string-valued parameters from the operating
system with the function confstr:
The normal return value from confstr is the length of the string
value that you asked for. If you supply a null pointer for buf,
then confstr does not try to store the string; it just returns
its length. A value of 0 indicates an error.
If the string you asked for is too long for the buffer (that is, longer
than len - 1), then confstr stores just that much
(leaving room for the terminating null character). You can tell that
this has happened because confstr returns a value greater than or
equal to len.
The following errno error conditions are defined for this function:
EINVAL
Currently there is just one parameter you can read with confstr:
_CS_PATH
_CS_LFS_CFLAGS
_LARGEFILE_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS_LDFLAGS
_LARGEFILE_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS_LIBS
_LARGEFILE_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS_LINTFLAGS
_LARGEFILE_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS64_CFLAGS
_LARGEFILE64_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS64_LDFLAGS
_LARGEFILE64_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS64_LIBS
_LARGEFILE64_SOURCE feature select macro; see section Feature Test Macros.
_CS_LFS64_LINTFLAGS
_LARGEFILE64_SOURCE feature select macro; see section Feature Test Macros.
The way to use confstr without any arbitrary limit on string size
is to call it twice: first call it to get the length, allocate the
buffer accordingly, and then call confstr again to fill the
buffer, like this:
char *
get_default_path (void)
{
size_t len = confstr (_CS_PATH, NULL, 0);
char *buffer = (char *) xmalloc (len);
if (confstr (_CS_PATH, buf, len + 1) == 0)
{
free (buffer);
return NULL;
}
return buffer;
}
Go to the first, previous, next, last section, table of contents.