std::filesystem::canonical, std::filesystem::weakly_canonical
std::filesystem::canonical, std::filesystem::weakly_canonical
Defined in header <filesystem>
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---|---|---|
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(1) | (since C++17) |
|
(2) | (since C++17) |
|
(3) | (since C++17) |
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(4) | (since C++17) |
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
#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"
See also
(C++17) |
represents a path (class) |
(C++17) |
composes an absolute path (function) |
(C++17) |
composes a relative path (function) |
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