std::filesystem::create_directory, std::filesystem::create_directories

From cppreference.com
< cpplrm; | filesystem
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 p already exists, the function does nothing (this condition is not treated as an error).
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).

The non-throwing overloads return false if any error occurs.

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

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

Example

#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

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