Difference between revisions of "cpp/filesystem/equivalent"
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{{cpp/filesystem/navbar}} | {{cpp/filesystem/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | filesystem}} | + | {{dcl header|filesystem}} |
| − | {{dcl | num=1 | since=c++17 | 1= | + | {{dcl|num=1|since=c++17|1= |
bool equivalent( const std::filesystem::path& p1, | bool equivalent( const std::filesystem::path& p1, | ||
const std::filesystem::path& p2 ); | const std::filesystem::path& p2 ); | ||
| + | }} | ||
| + | {{dcl|num=2|since=c++17|1= | ||
bool equivalent( const std::filesystem::path& p1, | bool equivalent( const std::filesystem::path& p1, | ||
const std::filesystem::path& p2, | const std::filesystem::path& p2, | ||
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{{dcl end}} | {{dcl end}} | ||
| − | Checks whether the paths {{ | + | Checks whether the paths {{c|p1}} and {{c|p2}} resolve to the same file system entity. |
| − | If either {{ | + | If either {{c|p1}} or {{c|p2}} does not exist, an error is reported. |
| − | The non-throwing overload returns {{ | + | The non-throwing overload returns {{c|false}} on errors. |
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | p1, p2 | paths to check for equivalence}} | + | {{par|p1, p2|paths to check for equivalence}} |
| − | {{par | ec | out-parameter for error reporting in the non-throwing overload }} | + | {{par|ec|out-parameter for error reporting in the non-throwing overload}} |
{{par end}} | {{par end}} | ||
===Return value=== | ===Return value=== | ||
| − | {{c|true}} if the {{ | + | {{c|true}} if the {{c|p1}} and {{c|p2}} refer to the same file or directory and their file status is the same. {{c|false}} otherwise. |
===Exceptions=== | ===Exceptions=== | ||
| − | {{cpp/filesystem/error_handling|p1|p2}} | + | {{cpp/filesystem/error_handling|p1|p2|throw=1/2}} |
===Notes=== | ===Notes=== | ||
| − | Two paths are considered to resolve to the same file system entity if the two candidate entities the paths resolve to are located on the same device at the same location. For POSIX, this means that the {{tt|st_dev}} and {{tt|st_ino}} members of their POSIX [ | + | Two paths are considered to resolve to the same file system entity if the two candidate entities the paths resolve to are located on the same device at the same location. For POSIX, this means that the {{tt|st_dev}} and {{tt|st_ino}} members of their POSIX [https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_stat.h.html {{tt|stat}} structure], obtained as if by POSIX [https://pubs.opengroup.org/onlinepubs/9699919799/functions/stat.html {{tt|stat()}}], are equal. |
In particular, all hard links for the same file or directory are equivalent, and a symlink and its target on the same file system are equivalent. | In particular, all hard links for the same file or directory are equivalent, and a symlink and its target on the same file system are equivalent. | ||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
===Example=== | ===Example=== | ||
| − | {{example|code= | + | {{example |
| − | + | |code= | |
#include <cstdint> | #include <cstdint> | ||
#include <filesystem> | #include <filesystem> | ||
| + | #include <iostream> | ||
namespace fs = std::filesystem; | namespace fs = std::filesystem; | ||
| + | |||
int main() | int main() | ||
{ | { | ||
| Line 51: | Line 50: | ||
fs::path p1 = "."; | fs::path p1 = "."; | ||
fs::path p2 = fs::current_path(); | fs::path p2 = fs::current_path(); | ||
| − | if(fs::equivalent(p1, p2)) | + | if (fs::equivalent(p1, p2)) |
std::cout << p1 << " is equivalent to " << p2 << '\n'; | std::cout << p1 << " is equivalent to " << p2 << '\n'; | ||
// symlink equivalency | // symlink equivalency | ||
| − | for(const fs::path lib : {"/lib/libc.so.6", "/lib/x86_64-linux-gnu/libc.so.6"}) { | + | for (const fs::path lib : {"/lib/libc.so.6", "/lib/x86_64-linux-gnu/libc.so.6"}) |
| − | try { | + | { |
| − | + | try | |
| − | } catch(std::filesystem::filesystem_error const& ex) { | + | { |
| + | p2 = lib.parent_path() / fs::read_symlink(lib); | ||
| + | } | ||
| + | catch (std::filesystem::filesystem_error const& ex) | ||
| + | { | ||
std::cout << ex.what() << '\n'; | std::cout << ex.what() << '\n'; | ||
continue; | continue; | ||
} | } | ||
| − | if(fs::equivalent(lib, p2)) | + | |
| + | if (fs::equivalent(lib, p2)) | ||
std::cout << lib << " is equivalent to " << p2 << '\n'; | std::cout << lib << " is equivalent to " << p2 << '\n'; | ||
} | } | ||
| Line 68: | Line 72: | ||
|p=true | |p=true | ||
|output= | |output= | ||
| − | "." is equivalent to "/tmp/ | + | "." is equivalent to "/var/tmp/test" |
filesystem error: read_symlink: No such file or directory [/lib/libc.so.6] | filesystem error: read_symlink: No such file or directory [/lib/libc.so.6] | ||
"/lib/x86_64-linux-gnu/libc.so.6" is equivalent to "/lib/x86_64-linux-gnu/libc-2.23.so" | "/lib/x86_64-linux-gnu/libc.so.6" is equivalent to "/lib/x86_64-linux-gnu/libc-2.23.so" | ||
}} | }} | ||
| + | |||
| + | ===Defect reports=== | ||
| + | {{dr list begin}} | ||
| + | {{dr list item|dr=2937|wg=lwg|std=C++17|before=error condition specified incorrectly|after=corrected}} | ||
| + | {{dr list end}} | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/filesystem/dsc status}} | + | {{dsc inc|cpp/filesystem/path/dsc compare}} |
| + | {{dsc inc|cpp/filesystem/path/dsc operator_cmp}} | ||
| + | {{dsc inc|cpp/filesystem/dsc status}} | ||
{{dsc end}} | {{dsc end}} | ||
| − | {{langlinks|ja|zh}} | + | {{langlinks|es|ja|ru|zh}} |
Latest revision as of 22:47, 8 September 2023
| Defined in header <filesystem>
|
||
| bool equivalent( const std::filesystem::path& p1, const std::filesystem::path& p2 ); |
(1) | (since C++17) |
| bool equivalent( const std::filesystem::path& p1, const std::filesystem::path& p2, |
(2) | (since C++17) |
Checks whether the paths p1 and p2 resolve to the same file system entity.
If either p1 or p2 does not exist, an error is reported.
The non-throwing overload returns false on errors.
Contents |
[edit] Parameters
| p1, p2 | - | paths to check for equivalence |
| ec | - | out-parameter for error reporting in the non-throwing overload |
[edit] Return value
true if the p1 and p2 refer to the same file or directory and their file status is the same. false otherwise.
[edit] Exceptions
Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.
1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p1 as the first path argument, p2 as the second path argument, and the OS error code as the error code argument.
2) Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.clear() if no errors occur.
[edit] Notes
Two paths are considered to resolve to the same file system entity if the two candidate entities the paths resolve to are located on the same device at the same location. For POSIX, this means that the st_dev and st_ino members of their POSIX stat structure, obtained as if by POSIX stat(), are equal.
In particular, all hard links for the same file or directory are equivalent, and a symlink and its target on the same file system are equivalent.
[edit] Example
Run this code
#include <cstdint> #include <filesystem> #include <iostream> namespace fs = std::filesystem; int main() { // hard link equivalency fs::path p1 = "."; fs::path p2 = fs::current_path(); if (fs::equivalent(p1, p2)) std::cout << p1 << " is equivalent to " << p2 << '\n'; // symlink equivalency for (const fs::path lib : {"/lib/libc.so.6", "/lib/x86_64-linux-gnu/libc.so.6"}) { try { p2 = lib.parent_path() / fs::read_symlink(lib); } catch (std::filesystem::filesystem_error const& ex) { std::cout << ex.what() << '\n'; continue; } if (fs::equivalent(lib, p2)) std::cout << lib << " is equivalent to " << p2 << '\n'; } }
Possible output:
"." is equivalent to "/var/tmp/test" filesystem error: read_symlink: No such file or directory [/lib/libc.so.6] "/lib/x86_64-linux-gnu/libc.so.6" is equivalent to "/lib/x86_64-linux-gnu/libc-2.23.so"
[edit] 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 2937 | C++17 | error condition specified incorrectly | corrected |
[edit] See also
| compares the lexical representations of two paths lexicographically (public member function of std::filesystem::path)
| |
| (C++17)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++17)(until C++20)(C++20) |
lexicographically compares two paths (function) |
| (C++17)(C++17) |
determines file attributes determines file attributes, checking the symlink target (function) |
