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ABS2REL(3) FreeBSD Library Functions Manual ABS2REL(3)
NAME
abs2rel - make a relative path name from an absolute path name
SYNOPSIS
char *
abs2rel(const char *path, const char *base, char *result, size_t size);
DESCRIPTION
The abs2rel() function makes a relative path name from an absolute path
name path based on a directory base and copies the resulting path name
into the memory referenced by result. The result argument must refer to
a buffer capable of storing at least size characters.
The resulting path name may include symbolic links. The abs2rel()
function doesn't check whether or not any path exists.
RETURN VALUES
The abs2rel() function returns relative path name on success. If an
error occurs, it returns NULL.
EXAMPLES
char result[MAXPATHLEN];
char *path = abs2rel("/usr/src/sys", "/usr/local/lib", result,
MAXPATHLEN);
yields:
path == "../../src/sys"
Similarly,
path1 = abs2rel("/usr/src/sys", "/usr", result, MAXPATHLEN);
path2 = abs2rel("/usr/src/sys", "/usr/src/sys", result, MAXPATHLEN);
yields:
path1 == "src/sys"
path2 == "."
ERRORS
The abs2rel() function may fail and set the external variable errno to
indicate the error.
[EINVAL] The base directory isn't an absolute path name or the
size argument is zero.
[ERANGE] The size argument is greater than zero but smaller
than the length of the pathname plus 1.
SEE ALSO
rel2abs(3)
AUTHORS
Shigio Yamaguchi (shigio@tamacom.com)
BUGS
path == "../usr/local/lib" /* It's wrong!! */
You should convert the base directory into a real path in advance.
path = abs2rel("/sys/kern", realpath("/sys", resolvedname), result,
MAXPATHLEN);
yields:
path == "../../../sys/kern" /* It's correct but ... */
That is correct, but a little redundant. If you wish get the simple
answer 'kern', do the following.
path = abs2rel(realpath("/sys/kern", r1), realpath("/sys", r2),
result, MAXPATHLEN);
The realpath() function assures correct result, but don't forget that
realpath() requires that all but the last component of the path exist.
FreeBSD 14.0-RELEASE-p6 August 7, 2022 FreeBSD 14.0-RELEASE-p6