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

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Filesystem library

Classes
filesystem::path filesystem::filesystem_error filesystem::directory_entry filesystem::directory_iterator filesystem::recursive_directory_iterator filesystem::file_status	filesystem::space_info filesystem::file_type filesystem::perms filesystem::perm_options filesystem::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::canonicalfilesystem::weakly_canonical filesystem::relativefilesystem::proximate filesystem::copy filesystem::copy_file filesystem::copy_symlink filesystem::create_directory filesystem::create_directories filesystem::create_hard_link filesystem::create_symlink filesystem::create_directory_symlink filesystem::current_path	filesystem::exists filesystem::equivalent filesystem::file_size filesystem::hard_link_count filesystem::last_write_time filesystem::permissions filesystem::read_symlink filesystem::remove filesystem::remove_all filesystem::rename filesystem::resize_file filesystem::space filesystem::status filesystem::symlink_status filesystem::temp_directory_path
File types
filesystem::is_block_file filesystem::is_character_file filesystem::is_directory filesystem::is_empty filesystem::status_known	filesystem::is_fifo filesystem::is_other filesystem::is_regular_file filesystem::is_socket filesystem::is_symlink

 

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.

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.

Notes

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

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

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 " << canonical(p) << '\n';
}

Possible output:

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

See also

path (C++17)	represents a path (class)
absolute (C++17)	composes an absolute path (function)
relativeproximate (C++17)	composes a relative path (function)