open 函数

需要用到的头文件：

include

include

include

include

include //lseek

mode 是八进制权限，比如0644，或者0755 等。也可以是使用系统已定义的

S_IRWXU 00700 user (file owner) has read, write, and execute permission //用户可读写执行权限

S_IRUSR 00400 user has read permission//用户写权限

S_IWUSR 00200 user has write permission//用户写权限

S_IXUSR 00100 user has execute permission//用户执行权限 （更多选项可查询man手册:man 2 open）