Std::filesystem::canonical,std::filesystem::weakly_canonical (3) Linux Manual Page

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

Synopsis

Defined in header<filesystem>

    path canonical(const std::filesystem::path &p);
(1)(since C++ 17)

    path canonical(const std::filesystem::path &p, (2)(since C++ 17)

                                                       std::error_code &ec);

path weakly_canonical(const std::filesystem::path &p);
(3)(since C++ 17)

    path weakly_canonical(const std::filesystem::path &p, (4)(since C++ 17)

                                                              std::error_code &ec);
1-2) 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 std::filesystem::absolute(p). The path p must exist.

3-4) Returns a path composed by operator/= from the result of calling canonical() 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.

Parameters

p – a path which may be absolute or relative; for canonical it must be an existing path
ec – error code to store error status to

Return value

1-2) An absolute path that resolves to the same file as std::filesystem::absolute(p).
3-4) 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

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 path argument and the OS error code as the error code argument. 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. Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

Notes

The function canonical() is modeled after the POSIX realpath.
The function weakly_canonical() was introduced to simplify operational semantics of relative().
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
LWG_2956 C++17 canonical has a spurious base parameter removed

Example

// Run this code

#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 " << fs::canonical(p) << '\n';
}

Possible output:

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

std::filesystem::canonical,std::filesystem::weakly_canonical (3) Linux Manual Page