How to get the absolute path for a given relative path programmatically in Linux?
Incase of Windows we have the _fullpath() API. In other words, I mean what is analogous API to _fullpath of Windows in Linux?
7 Answers
As Paul mentioned, use realpath(). Please note though, that since many file systems in Linux support hard links, any given directory can have a number of different absolute paths.
8 Comments
Vatine
Any given file can, for sure. Hard-links to directories isn't necessarily supported. Symlinks also cause some confusion when it come sto determining the "real" path.
Jay
@unwind, Thanks for the Info. If due to hard links, if a given directory resolves to multiple different absolute paths, what will be the behaviour of realpath API?
edgar.holleis
Hardlinks to directories are considered evil and forbidden by most filesystems.
Jay
I am a little confused. Is it possible that a given directory resolves to many different absolute paths? If yes, then what will be the behaviour realpath?
Otto Allmendinger
@Jay it doesn't affect resolving a relative path to an absolute path.
|
Check out the realpath function.
#include <stdlib.h>
#include <stdio.h>
#include <linux/limits.h>
int main()
{
char resolved_path[PATH_MAX];
realpath("../../", resolved_path);
printf("\n%s\n",resolved_path);
return 0;
}
3 Comments
Speed8ump
Please use PATH_MAX instead of 100
Steve Dodier-Lazaro
This code is insecure and buggy, as pointed out above. Do not give such a small buffer to
realpath which will most likely write beyond the buffer size (since it requires a length of PATH_MAX). Even if the program doesn't crash, this code could lead to security vulnerabilities depending on the variable layout, if an adversary can control the original path to be resolved. The manual recommends passing NULL as a second parameter and letting realpath allocate memory to ensure no issues with PATH_MAX definitions, starting with POSIX 2008.
Ciro Costa
I think it is a good think to always remember that PATH_MAX simply isn't: insanecoding.blogspot.com.br/2007/11/pathmax-simply-isnt.html
There is the realpath from stdlib.h
2 Comments
Dan Moulding
I immediately thought of realpath, too, but I was stunned -- stunned I say -- when I saw your answer showing that
realpath is in stdlib.h. Surely that can't be true, considering that realpath is not part of the C library. Lo and behold, it's true. I'm dumbfounded. What's a well-formed program that defines its own function named realpath to do? Those POSIX guys have run amok! Amok I say!
caf
Dan: So long as they invoke their compiler in "strictly conforming" mode and don't define any macros that invoke undefined behaviour (like
_XOPEN_SOURCE), they should be OK.Running on RedHat 5.3, realpath doesn't exist but readlink is installed. You can use it on relative paths and symlinks, plus it will resolve symlinks recursively for you. It's thus a better option that realpath in my opinion
readlink -f .
Comments
The is also another useful way, like "readlink -m $filename"
First of all, it works without requirement for target file to exist. Secondly, it will handle symlinks and get really real path.
Comments
// For C++ with Gnome Gtkmm3 libraries
#include <glibmm.h>
#include <giomm.h>
string PathRel2Abs(string relpath) {
Glib::RefPtr<Gio::File> file = Gio::File::create_for_path(relpath);
return file->get_path();
}
2 Comments
Caleb Kleveter
Usually it is a good idea to add some explanation to your post on how the code works. This helps newer developers know what the code does.
Nisse Engström
And it's not even C.
c, this is probably a duplicate of stackoverflow.com/questions/229012/…