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::copy_options filesystem::directory_options filesystem::file_time_type
Functions
filesystem::absolute filesystem::system_complete 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. 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

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)
absolutesystem_complete (C++17)(C++17)	composes an absolute path converts a path to an absolute path replicating OS-specific behavior (function)
relativeproximate (C++17)	composes a relative path (function)