如何将文件权限打印为字符串? [英] How do I print file permissions as a string?

问题描述

我有一个 mode_t perms 变量，它存储从另一个函数返回的文件的权限.我需要将文件权限打印为

I have a mode_t perms variable which stores the permission for a file returned from another function. I need to print the file permissions as a tring, of the form

rw-r--r-- (0644)

但我得到的是

r--r--r-- (100644)

我怎样才能获得正确的权限?我试过谷歌搜索，但不明白我做错了什么.这是我的代码:

How can I get the right permissions? I've tried googling and don't understand what I'm doing wrong. Here's my code:

    void print_perms(mode_t perms)
    {
        printf( (perms & S_IRUSR) ? "r" : "-");
        printf( (perms & S_IWUSR) ? "w" : "-");
        printf( (perms & S_IXUSR) ? "x" : "-");
        printf( (perms & S_IRGRP) ? "r" : "-");
        printf( (perms & S_IWGRP) ? "w" : "-");
        printf( (perms & S_IXGRP) ? "x" : "-");
        printf( (perms & S_IROTH) ? "r" : "-");
        printf( (perms & S_IWOTH) ? "w" : "-");
        printf( (perms & S_IXOTH) ? "x" : "-");
    }
//later
print_perms(permissions);
printf(" (%d)\n", permissions);

推荐答案

首先，UNIX 的文件权限通常以八进制表示，对应的格式字符串是%o"，而不是%d".rw-r--r--实际上是0644，但是在C语言中0644 == 420，例如(后者是十进制的).

First, UNIX file permissions are conventionally expressed in octal, corresponding format string is "%o", not "%d". rw-r--r-- is really 0644, but in C language 0644 == 420, for example (the latter is in decimal).

其次，使用的位比代码中指定的 9 多.你实际上应该说类似

Second, there are more bits used than 9 specified in the code. You actually should say something like

printf(" (%3o)", perms&0777);

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