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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. 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.

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

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

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. This overload has

noexcept specification:

noexcept

Notes

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

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

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"