std::filesystem::canonical, std::filesystem::weakly_canonical

Defined in header <filesystem>
path canonical( const std::filesystem::path& p,
                const std::filesystem::path& base = std::filesystem::current_path() );
(1) (since C++17)
path canonical( const std::filesystem::path& p,
                std::error_code& ec );
(2) (since C++17)
path canonical( const std::filesystem::path& p,

                const std::filesystem::path& base,

                std::error_code& ec );
(3) (since C++17)
path weakly_canonical(const std::filesystem::path& p);
(4) (since C++17)
path weakly_canonical(const std::filesystem::path& p,
                      std::error_code& ec);
(5) (since C++17)
1-3) Converts path p to a canonical absolute path, i.e. an absolute path that has no dot, dot-dot elements or symbolic links in its generic format representation. If p is not an absolute path, the function behaves as if it is first made absolute by absolute(p, base) or absolute(p) for (2). The path p must exist.
4-5) Returns a path composed by operator/= from the result of calling canonical() without a base argument and with a path argument composed of the leading elements of p that exist (as determined by status(p) or status(p, ec)), if any, followed by the elements of p that do not exist, if any. The resulting path is in normal form.


[edit] Parameters

p - a path which may be absolute or relative to base, and which must be an existing path
base - base path to be used in case p is relative
ec - error code to store error status to

[edit] Return value

1-3) An absolute path that resolves to the same file as absolute(p, base) (or absolute(p) for (2)).
4-5) A normal path of the form canonical(x)/y, where x is a path composed of the longest leading sequence of elements in p that exist, and y is a path composed of the remaining trailing non-existent elements of p

[edit] Exceptions

The overload that does not take a std::error_code& parameter throws filesystem_error on underlying OS API errors, constructed with p as the first argument, base as the second argument, and the OS error code as the error code argument. std::bad_alloc may be thrown if memory allocation fails. The overload taking a std::error_code& parameter sets it to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur.

[edit] Notes

The function canonical() is modeled after the POSIX realpath.

The function weakly_canonical() was introduced to simplify operational semantics of relative().

[edit] Example

#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
int main()
    fs::path p = fs::path("..") / ".." / "AppData";
    std::cout << "Current path is " << fs::current_path() << '\n'
              << "Canonical path for " << p << " is " << canonical(p) << '\n';

Possible output:

Current path is "C:\Users\abcdef\AppData\Local\Temp"
Canonical path for "..\..\AppData" is "C:/Users\abcdef\AppData"

[edit] See also

represents a path
(class) [edit]
composes an absolute path
(function) [edit]
composes a relative path
(function) [edit]