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Difference between revisions of "cpp/filesystem/create directory"

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(Remove CreateDirectoryExW note. First, on some OSes, that API isn't available, so we (MSVC++) never called that there. Second, it turns out that for a symlink CreateDirectoryExW has copy_symlink behavior, not create_directory behavior)
(P1164R1)
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{{dcl end}}
 
{{dcl end}}
  
−
@1@ Creates the directory {{tt|p}} as if by POSIX [http://pubs.opengroup.org/onlinepubs/9699919799/functions/mkdir.html mkdir()] with a second argument of {{c|static_cast<int>(std::filesystem::perms::all)}} (the parent directory must already exist). If {{tt|p}} already exists, the function does nothing (this condition is not treated as an error).  
+
@1@ Creates the directory {{tt|p}} as if by POSIX [http://pubs.opengroup.org/onlinepubs/9699919799/functions/mkdir.html {{tt|mkdir()}}] with a second argument of {{c|static_cast<int>(std::filesystem::perms::all)}} (the parent directory must already exist). If the function fails because {{tt|p}} resolves to an existing directory, no error is reported. Otherwise on failure an error is reported.
 
@2@ Same as {{v|1}}, except that the attributes of the new directory are copied from {{tt|existing_p}} (which must be a directory that exists). It is OS-dependent which attributes are copied: on POSIX systems, the attributes are copied as if by
 
@2@ Same as {{v|1}}, except that the attributes of the new directory are copied from {{tt|existing_p}} (which must be a directory that exists). It is OS-dependent which attributes are copied: on POSIX systems, the attributes are copied as if by
 
{{source|1=
 
{{source|1=
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}}On Windows OS, no attributes of {{tt|existing_p}} are copied.
 
}}On Windows OS, no attributes of {{tt|existing_p}} are copied.
 
@3@ Executes {{v|1}} for every element of {{tt|p}} that does not already exist. If {{tt|p}} already exists, the function does nothing (this condition is not treated as an error).
 
@3@ Executes {{v|1}} for every element of {{tt|p}} that does not already exist. If {{tt|p}} already exists, the function does nothing (this condition is not treated as an error).
−
 
−
The non-throwing overloads return {{c|false}} if any error occurs.
 
  
 
===Parameters===
 
===Parameters===
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===Notes===
 
===Notes===
−
The attribute-preserving overload {{v|2}} is implicitly invoked by {{ltt|cpp/filesystem/copy|copy()}} when recursively copying directories. Its equivalent in boost.filesystem is [http://www.boost.org/doc/libs/1_57_0/libs/filesystem/doc/reference.html#copy_directory copy_directory] (with argument order reversed)
+
The attribute-preserving overload {{v|2}} is implicitly invoked by {{ltt|cpp/filesystem/copy|copy()}} when recursively copying directories. Its equivalent in boost.filesystem is [http://www.boost.org/doc/libs/1_57_0/libs/filesystem/doc/reference.html#copy_directory {{tt|copy_directory}}] (with argument order reversed)
  
 
===Defect reports===
 
===Defect reports===
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{{dr list item|wg=lwg|dr=2935|std=C++17|before=error if target already exists but isn't a directory|after=not error}}
 
{{dr list item|wg=lwg|dr=2935|std=C++17|before=error if target already exists but isn't a directory|after=not error}}
 
{{dr list item|wg=lwg|dr=3014|std=C++17|before={{tt|error_code}} overload of {{tt|create_directories}} marked noexcept but can allocate memory|after=noexcept removed}}
 
{{dr list item|wg=lwg|dr=3014|std=C++17|before={{tt|error_code}} overload of {{tt|create_directories}} marked noexcept but can allocate memory|after=noexcept removed}}
 +
{{dr list item|paper=P1164R1|std=C++17|before=creation failure caused by an existing file is not an error|after=made error}}
 
{{dr list end}}
 
{{dr list end}}
  

Revision as of 00:41, 11 May 2019

 
C++
 
Filesystem library
Classes
Functions
File types
 
Defined in header <filesystem>
bool create_directory( const std::filesystem::path& p );
bool create_directory( const std::filesystem::path& p, std::error_code& ec ) noexcept;
 (1) (since C++17)
bool create_directory( const std::filesystem::path& p,

                       const std::filesystem::path& existing_p );
bool create_directory( const std::filesystem::path& p,
                       const std::filesystem::path& existing_p,

                       std::error_code& ec ) noexcept;
 (2) (since C++17)
bool create_directories( const std::filesystem::path& p );
bool create_directories( const std::filesystem::path& p, std::error_code& ec );
 (3) (since C++17)
1) Creates the directory p as if by POSIX mkdir() with a second argument of static_cast<int>(std::filesystem::perms::all) (the parent directory must already exist). If the function fails because p resolves to an existing directory, no error is reported. Otherwise on failure an error is reported.
2) Same as (1), except that the attributes of the new directory are copied from existing_p (which must be a directory that exists). It is OS-dependent which attributes are copied: on POSIX systems, the attributes are copied as if by 
stat(existing_p.c_str(), &attributes_stat)
mkdir(p.c_str(), attributes_stat.st_mode)
On Windows OS, no attributes of existing_p are copied.
3) Executes (1) for every element of p that does not already exist. If p already exists, the function does nothing (this condition is not treated as an error).

Contents

Parameters

p - the path to the new directory to create
existing_p - the path to a directory to copy the attributes from
ec - out-parameter for error reporting in the non-throwing overload

Return value

true if a directory was created for the directory p resolves to, false otherwise.

Exceptions

1,3) Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

The overload that does not take a std::error_code& parameter throws std::filesystem::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.
2) Any overload not marked noexcept may throw std::bad_alloc if memory allocation fails.

The overload that does not take a std::error_code& parameter throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument, existing_p as the second 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.

Notes

The attribute-preserving overload (2) is implicitly invoked by copy() when recursively copying directories. Its equivalent in boost.filesystem is copy_directory (with argument order reversed)

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 2935 C++17 error if target already exists but isn't a directory not error
LWG 3014 C++17 error_code overload of create_directories marked noexcept but can allocate memory noexcept removed
P1164R1 C++17 creation failure caused by an existing file is not an error made error

Example

Run this code
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <filesystem>
namespace fs = std::filesystem;
 
int main()
{
    fs::create_directories("sandbox/1/2/a");
    fs::create_directory("sandbox/1/2/b");
    fs::permissions("sandbox/1/2/b", fs::perms::remove_perms | fs::perms::others_all);
    fs::create_directory("sandbox/1/2/c", "sandbox/1/2/b");
    std::system("ls -l sandbox/1/2");
    fs::remove_all("sandbox");
}

Possible output: 

drwxr-xr-x 2 user group 4096 Apr 15 09:33 a
drwxr-x--- 2 user group 4096 Apr 15 09:33 b
drwxr-x--- 2 user group 4096 Apr 15 09:33 c

See also

(C++17)(C++17)
 creates a symbolic link
(function) [edit]
(C++17)
 copies files or directories
(function) [edit]
(C++17)
 identifies file system permissions
(enum) [edit]
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