c - O_RDWR 权限被拒绝

Question

我创建了这个文件

char *output = "big";
creat(output, O_RDWR);

当我尝试读取文件时

 cat big

我的权限被拒绝了。我的代码有什么问题？如何创建具有读写权限模式的文件？

用ls -l，big的权限是这样的

----------

这是什么意思？

Answer 1

您误解了模式参数。从手册页:

          mode specifies the permissions to use in case a new file is cre‐
          ated.  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  only  applies  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.

还有

   creat()    is    equivalent    to    open()   with   flags   equal   to
   O_CREAT|O_WRONLY|O_TRUNC.

因此，更合适的调用可能如下所示:

int fd = creat(output, 0644); /*-rw-r--r-- */

如果你想打开它O_RDWR，那么只需使用open():

int fd = open(output, O_CREAT|O_RDWR|O_TRUNC, 0644);