open() 函数参数 [英] open() function parameters

问题描述

如果您通过考虑最后一个参数0"来查看下面的代码块，写行是否正常工作?

If you look at this code block below by taking into consideration the last parameter "0", Does write line work properly ?

filename = argv[1];
string = "Example string";
if (stat(argv[1], &buf) != 0)
{
    fd = open(filename, O_WRONLY | O_CREAT, 0);
    if (fd < 0)
    {
        perror(filename);
        exit(1);
    }
    write(fd, string, strlen(string));
    close(fd);
}
else
{
    print("%s file exists\n", filename);
}

推荐答案

来自手册页:

mode 指定在创建新文件时使用的权限.在标志中指定 O_CREAT 时必须提供此参数；如果未指定 O_CREAT，则忽略 mode.进程的 umask 以通常的方式修改有效权限:创建的文件的权限是 (mode & ~umask).请注意，此模式仅适用于新创建的文件的未来访问；创建只读文件的 open() 调用很可能会返回一个读/写文件描述符.

mode specifies the permissions to use in case a new file is created. This argument must be supplied when O_CREAT is specified in flags; if O_CREAT is not specified, then mode is ignored. The effective permissions are modified by the process's umask in the usual way: The permissions of the created file are (mode & ~umask). Note that this mode applies only to future accesses of the newly created file; the open() call that creates a read-only file may well return a read/write file descriptor.

为模式提供了以下符号常量:

The following symbolic constants are provided for mode:

S_IRWXU  00700 user (file owner) has read, write and execute permission
S_IRUSR  00400 user has read permission
S_IWUSR  00200 user has write permission
S_IXUSR  00100 user has execute permission
S_IRWXG  00070 group has read, write and execute permission
S_IRGRP  00040 group has read permission
S_IWGRP  00020 group has write permission
S_IXGRP  00010 group has execute permission
S_IRWXO  00007 others have read, write and execute permission
S_IROTH  00004 others have read permission
S_IWOTH  00002 others have write permission
S_IXOTH  00001 others have execute permission

因此，将 mode 指定为零，您将创建一个文件，其权限为 0 &~umask，即一个没有任何权限的文件.

So, specifying a mode of zero, you will create a file with the permissions of 0 & ~umask, i.e. a file without any permissions.

文件系统的具体内容不在 open() 或 write() 函数的范围内.

What exactly the filesystem makes of this is not in the domain of the open() or write() functions.

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