access判断文件是否存在，是否可读可写等

   #include <unistd.h>

    if((access("/data/test.c",F_OK))!=-1){

        //printf("文件 test.c 存在. ");

    }

 

DESCRIPTION

       access() checks whether the calling process can access the file pathname.  If pathname is a symbolic link, it is dereferenced.

       The  mode specifies the accessibility check(s) to be performed, and is either the value F_OK, or a mask consisting of the bitwise OR of one or more of R_OK,

       W_OK, and X_OK.  F_OK tests for the existence of the file.  R_OK, W_OK, and X_OK test whether the file exists and grants read, write,  and  execute  permis‐

       sions, respectively.

       The  check  is  done  using  the  calling  process's real UID and GID, rather than the effective IDs as is done when actually attempting an operation (e.g.,

       open(2)) on the file.  This allows set-user-ID programs to easily determine the invoking user's authority.

       If the calling process is privileged (i.e., its real UID is zero), then an X_OK check is successful for a regular file if execute permission is enabled  for

       any of the file owner, group, or other.