std::filesystem::perms

Defined in header <filesystem>
enum class perms;		(since C++17)

此类型表示文件访问权限。perms满足…的要求BitmaskType%28，这意味着按位运算符operator&，，，operator|，，，operator^，，，operator~，，，operator&=，，，operator|=，和operator^=为此类型%29定义。

访问权限模型POSIX权限位报告的任何单个文件权限%28地位%29是以下几个比特的组合：

成员常数

Member constant	Value (octal)	POSIX equivalent	Meaning
none	0		no permission bits are set
owner_read	0400	S_IRUSR	File owner has read permission
owner_write	0200	S_IWUSR	File owner has write permission
owner_exec	0100	S_IXUSR	File owner has execute/search permission
owner_all	0700	S_IRWXU	File owner has read, write, and execute/search permissions Equivalent to owner_read \| owner_write \| owner_exec.
group_read	040	S_IRGRP	The file's user group has read permission
group_write	020	S_IWGRP	The file's user group has write permission
group_exec	010	S_IXGRP	The file's user group has execute/search permission
group_all	070	S_IRWXG	The file's user group has read, write, and execute/search permissions Equivalent to group_read \| group_write \| group_exec.
others_read	04	S_IROTH	Other users have read permission
others_write	02	S_IWOTH	Other users have write permission
others_exec	01	S_IXOTH	Other users have execute/search permission
others_all	07	S_IRWXO	Other users have read, write, and execute/search permissions Equivalent to others_read \| others_write \| others_exec.
all	0777		All users have read, write, and execute/search permissions Equivalent to owner_all \| group_all \| others_all.
set_uid	04000	S_ISUID	Set user ID to file owner user ID on execution
set_gid	02000	S_ISGID	Set group ID to file's user group ID on execution
sticky_bit	01000	S_ISVTX	Implementation-defined meaning, but POSIX XSI specifies that when set on a directory, only file owners may delete files even if the directory is writeable to others (used with /tmp)
mask	07777		All valid permission bits. Equivalent to all \| set_uid \| set_gid \| sticky_bit.

此外，定义了以下此类型的常量，这些常量不表示权限：

Member constant	Value (hex)	Meaning
unknown	0xFFFF	Unknown permissions (e.g. when file_status is created without permissions)
add_perms	0x10000	Control bit that instructs permissions to add, but not clear permission bits.
remove_perms	0x20000	Control bit that instructs permissions to clear, but not add permission bits
resolve_symlinks	0x40000	Control bit that instructs permissions to resolve symlinks

注记

权限可能不一定被实现为位，但它们在概念上被这样对待。

在某些系统上，某些权限位可能被忽略，而更改某些位可能会自动更改其他的%28例如。在没有所有者/组/所有区别的平台上，设置三位写入位中的任意一位设置所有三%29。

例

二次

#include <fstream>
#include <bitset>
#include <iostream>
#include <filesystem>
namespace fs = std::filesystem;
 
void demo_perms(fs::perms p)
{
    std::cout << ((p & fs::perms::owner_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::owner_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::owner_exec) != fs::perms::none ? "x" : "-")
              << ((p & fs::perms::group_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::group_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::group_exec) != fs::perms::none ? "x" : "-")
              << ((p & fs::perms::others_read) != fs::perms::none ? "r" : "-")
              << ((p & fs::perms::others_write) != fs::perms::none ? "w" : "-")
              << ((p & fs::perms::others_exec) != fs::perms::none ? "x" : "-")
              << '\n';
}
int main()
{
    std::ofstream("test.txt"); // create file
 
    std::cout << "Created file with permissions: ";
    demo_perms(fs::status("test.txt").permissions());
 
    fs::permissions("test.txt", fs::perms::add_perms |
                                fs::perms::owner_all | fs::perms::group_all);
 
    std::cout << "After adding o+rwx and g+rwx:  ";
    demo_perms(fs::status("test.txt").permissions());
 
    fs::remove("test.txt");
}

二次

可能的产出：

二次

Created file with permissions: rw-r--r--
After adding o+rwx and g+wrx:  rwxrwxr--

二次

另见

statussymlink_status (C++17)(C++17)	determines file attributesdetermines file attributes, checking the symlink target (function)
permissions (C++17)	modifies file access permissions (function)

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最后更新于：2017-12-18