非

~ 0 = 1
~ 1 = 0

可以用于整体翻转.

~ 1000 = 0111
~ 0100 = 1011

或

0 | 0 = 0
0 | 1 = 1
1 | 0 = 1
1 | 1 = 1

或,有真就是真.

x | 0 = x
x | 1 = 1

和0或是原值,和1或为1.可以用于打开某位的开关.

0011 | 1000 = 1011 # 打开本来关闭的
1011 | 1000 = 1011 # 打开本来打开的

与

0 & 0 = 0
0 & 1 = 0
1 & 0 = 0
1 & 1 = 1

与,都是真才真.

x & 0 = 0
x & 1 = x

和0与是0,和1与是原值.可以用于关闭某位的开关.

0011 & (~1000) = 0011 & 0111 = 0011 # 关闭本来关闭的
1011 & (~1000) = 1011 & 0111 = 0011 # 关闭本来打开的

异或

0 ^ 0 = 0
0 ^ 1 = 1
1 ^ 0 = 1
1 ^ 1 = 0

相同为零,不同为1.

x ^ 0 = x
x ^ 1 = (~x)

和0异或是本身,和1异或是取反.可以用来翻转某个位.

0011 ^ 0100 = 0111
0011 ^ 0000 = 0011
0011 ^ 1111 = 1100

例子

#include "apue.h"
#include <fcntl.h>

int main(int argc, const char * argv[]) {

    struct stat mStat;
    const char * file_path = "hi.txt";
    if(stat(file_path, &mStat) <0){
        err_sys("stat获取出错!\n");
    }

    // 在原有权限的基础上,关闭Other的RWX,打开User的RWX,设置用户ID位
    chmod(file_path, (mStat.st_mode & ~S_IRWXO) | S_IRWXU | S_ISUID);
    exit(0);
}


Baodong-MBP:chmod cbd$ chmod 0477 hi.txt
Baodong-MBP:chmod cbd$ ll hi.txt
-r--rwxrwx  1 cbd  staff  11  8 23 14:36 hi.txt*
Baodong-MBP:chmod cbd$ ./a.out
Baodong-MBP:chmod cbd$ ll hi.txt
-rwsrwx---  1 cbd  staff  11  8 23 14:36 hi.txt*

参考

/*
 * Copyright (c) 2003-2012 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 *
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */

/*
 * [XSI] The symbolic names for file modes for use as values of mode_t
 * shall be defined as described in <sys/stat.h>
 */
#ifndef S_IFMT
/* File type */
#define	S_IFMT		0170000		/* [XSI] type of file mask */
#define	S_IFIFO		0010000		/* [XSI] named pipe (fifo) */
#define	S_IFCHR		0020000		/* [XSI] character special */
#define	S_IFDIR		0040000		/* [XSI] directory */
#define	S_IFBLK		0060000		/* [XSI] block special */
#define	S_IFREG		0100000		/* [XSI] regular */
#define	S_IFLNK		0120000		/* [XSI] symbolic link */
#define	S_IFSOCK	0140000		/* [XSI] socket */
#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define	S_IFWHT		0160000		/* OBSOLETE: whiteout */
#endif

/* File mode */
/* Read, write, execute/search by owner */
#define	S_IRWXU		0000700		/* [XSI] RWX mask for owner */
#define	S_IRUSR		0000400		/* [XSI] R for owner */
#define	S_IWUSR		0000200		/* [XSI] W for owner */
#define	S_IXUSR		0000100		/* [XSI] X for owner */
/* Read, write, execute/search by group */
#define	S_IRWXG		0000070		/* [XSI] RWX mask for group */
#define	S_IRGRP		0000040		/* [XSI] R for group */
#define	S_IWGRP		0000020		/* [XSI] W for group */
#define	S_IXGRP		0000010		/* [XSI] X for group */
/* Read, write, execute/search by others */
#define	S_IRWXO		0000007		/* [XSI] RWX mask for other */
#define	S_IROTH		0000004		/* [XSI] R for other */
#define	S_IWOTH		0000002		/* [XSI] W for other */
#define	S_IXOTH		0000001		/* [XSI] X for other */

#define	S_ISUID		0004000		/* [XSI] set user id on execution */
#define	S_ISGID		0002000		/* [XSI] set group id on execution */
#define	S_ISVTX		0001000		/* [XSI] directory restrcted delete */

#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
#define	S_ISTXT		S_ISVTX		/* sticky bit: not supported */
#define	S_IREAD		S_IRUSR		/* backward compatability */
#define	S_IWRITE	S_IWUSR		/* backward compatability */
#define	S_IEXEC		S_IXUSR		/* backward compatability */
#endif
#endif	/* !S_IFMT */