使用open()在C中创建文件

Question

这是我第一次使用open():

#include <fcntl.h>

我正在尝试创建两个文件:

int fd;
int fd2;
char *tmpname = "./TMPFILE";
printf( "Temporary file created\n ");
char *tmpname2 = "./TMPFILE2";
printf( "Temporary file two created\n ");
fd = open(tmpname, O_WRONLY | O_APPEND);
fd2 = open(tmpname2, O_WRONLY | O_APPEND);

我正在尝试在当前工作目录中创建可以写入和追加的文件.

这编译并运行,但我担心的是,当我检查我的目录以查看文件是否已创建时,它们未列出.

我的问题是,open()只是制作程序运行后删除的临时文件,或者我搞砸了什么？

Answer 1

创建文件时,需要打开第三个参数(mode).如果你不这样做,就会发生不可预测的事情.

此外,如果你想创建一个文件,如果它不存在,你将需要或者O_CREAT进入,即

fd = open(tmpname, O_WRONLY | O_APPEND | O_CREAT, 0644);

O_CREAT (粗略地说)如果文件不存在则创建文件.

从手册页:

NAME
       open, creat - open and possibly create a file or device

SYNOPSIS
       #include 
       #include 
       #include 

       int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode);

       int creat(const char *pathname, mode_t mode);

...
       O_CREAT
              If the file does not exist it will be created.  The owner (user ID) of
              the  file  is  set to the effective user ID of the process.  The group
              ownership (group ID) is set either to the effective group  ID  of  the
              process  or  to  the  group  ID  of the parent directory (depending on
              filesystem type and mount options, and the mode of the  parent  direc?
              tory,  see  the  mount  options  bsdgroups and sysvgroups described in
              mount(8)).

              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 permis?
              sions  are  modified by the process's umask in the usual way: The per?
              missions 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.