Get absolute path with boost::filesystem::path

Question

My current working directory is located at /home/myuser/program, I created a boost::filesystem::path object pointing to it. I appended /../somedir so it becomes /home/myuser/program/../somedir. But I need to get its resolved absolute path, which would be /home/myuser/somedir.

I have been trying for long time and I do not find any method in their reference to do this. There is a method called make_absolute, which seems to be supposed to do what I expect, but I have to give it a “root” path argument. Which should it be? do I really need to do this to get the real absolute path? Is there any other way?

Solution 1

You say you want an absolute path, but your example shows that you already have an absolute path. The process of removing the .. components of a path is known as canonicalization. For that, you should call canonical. It happens to also perform the task of absolute, so you don't need to call absolute or make_absolute first. The make_absolute function requires a base path; you can pass it current_path() if you don't have anything better.

Solution 2

Update, since this still appears to be Google's top hit concerning absolute paths:

As of Boost 1.57, some of the previously suggested functions have since been removed.

The solution that worked for me was

boost::filesystem::path canonicalPath = boost::filesystem::canonical(previousPath, relativeTo);

(using the free-standing method canonical(), defined in boost/filesystem/operations.hpp, which is automatically included via boost/filesystem.hpp)

Important: calling canonical on a path that does not exist (e.g., you want to create a file) will throw an exception. In that case, your next best bet is probably boost::filesystem::absolute(). It will also work for non-existing paths, but won't get rid of dots in the middle of the path (as in a/b/c/../../d.txt). Note: Make sure relativeTo refers to a directory, calling parent_path() on paths referring to files (e.g. the opened file that contained a directory or file path relative to itself).

Solution 3

The documentation shows that the make_absolute has an optional second parameter that defaults to your current path:

path absolute(const path& p, const path& base=current_path());

Try it without the second parameter and see if it returns the results you're looking for.