linux之open函数解析

最新推荐文章于 2024-09-14 17:34:26 发布

fulinux

最新推荐文章于 2024-09-14 17:34:26 发布

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分类专栏： C 语言集合 APUE 集合 Linux函数篇文章标签： open linux apue

本文链接：https://blog.youkuaiyun.com/fulinus/article/details/9565571

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本文介绍了使用C语言进行文件操作的基本方法，并展示了如何将原始文件备份为后缀为.backup的副本，确保文件的安全性。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

一、

open.c

/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: open.c
* Description: This file
*
* Version: 1.0.0(07/27/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/27/2013 03:23:14 PM"
*
********************************************************************************/
#include <stdio.h>
#include <string.h>
#include <fcntl.h>

int main(void)
{
int fd;
if(fd = open("openfile", O_CREAT | O_RDWR, S_IRUSR|S_IWUSR|S_IXUSR))
printf("open is OK\n");
else
printf("open is not OK\n");

if(!close(fd))
printf("closed\n");
else
printf("not closed\n");

}

[lingyun@localhost apue]$ gcc open.c
[lingyun@localhost apue]$ ls
a.out open.c
[lingyun@localhost apue]$ ./a.out
open is OK
closed
[lingyun@localhost apue]$ ls
a.out open.c openfile
[lingyun@localhost apue]$

二、

[lingyun@localhost open_2]$ vim open.c
********************************************************************************/
perror("open");
printf("%s",str);
+ open.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: open.c
* Description: This file
*
* Version: 1.0.0(07/28/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/28/2013 12:04:54 PM"
*
********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>

int main(int argc,char *argv[])
{
int fd;
char str[10];

fd = open("hello.txt",O_RDONLY);

if(fd < 0)
{
perror("open");
}

while(read(fd,str,sizeof(str)) > 0)
{
printf("%s",str);
}

return 0;
}

~
~
~
~
~
~
~
~
~
~
~
~/apue/open_2/open.c[+] CWD: /usr/local/src/lingyun/apue/open_2 Line: 22/38:15
"open.c" [New] 38L, 875C written

[lingyun@localhost open_2]$ vim hello.txt
+ hello.txt
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
ok
~
~
~/apue/open_2/hello.txt[+] CWD: /usr/local/src/lingyun/apue/open_2 Line: 28/28:2
"hello.txt" [New] 28L, 543C written

[lingyun@localhost open_2]$ ls
hello.txt open.c
[lingyun@localhost open_2]$ gcc open.c
[lingyun@localhost open_2]$ ./a.out
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
hello world !!!!!!!
ok
!!!!!!
[lingyun@localhost open_2]$

三、

1 /*********************************************************************************
2 * Copyright: (C) 2013 fulinux<fulinux@sina.com>
3 * All rights reserved.
4 *
5 * Filename: open.c
6 * Description: This file
7 *
8 * Version: 1.0.0(07/28/2013~)
9 * Author: fulinux <fulinux@sina.com>
10 * ChangeLog: 1, Release initial version on "07/28/2013 12:14:31 PM"
11 *
12 ********************************************************************************/
13
14 #include <stdio.h>
15 #include <stdlib.h>
16 #include <string.h>
17 #include <fcntl.h>
18
19 int main(int argc,char *args[])
20 {
21
22 char buff[1024];
23 int fd1,fd2,i;
24 int baksize = sizeof(args[1]) + 7;
25 char bakfile[baksize];
26
27 /* input one file only */
28 if(argc != 2)
29 {
30 printf("Input one file a time!\n");
31 exit(1);
32 }
33
34 /* bakfile="XXX.backup" */
35 strcpy(bakfile,args[1]);
36 strcat(bakfile,".backup");
37
38 /* open() */
39 fd1 = open(args[1], O_RDONLY, 0644);
40 fd2 = open(bakfile, O_RDWR|O_CREAT|O_TRUNC);
41
42 if(fd1 < 0||(fd2 < 0))
43 {
44 printf("Open Error! Check if the file is exist and you have permission!\n");
45 exit(1);
46 }
47
48 /* read from fd1 and write buff to fd2 */
49 while((i = read(fd1,buff,sizeof(buff))) > 0)
50 {
51 write(fd2,buff,i);
52 }
53
54 close(fd1);
55 close(fd2);
56 printf("Backup done!\n");
57 exit(0);
58
59 }

[lingyun@localhost open_3]$ vim file.txt
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
end

[lingyun@localhost open_3]$ ls
a.out file.txt open.c

[lingyun@localhost open_3]$ ./a.out file.txt
Backup done!

a.out file.txt file.txt.backup open.c
[lingyun@localhost open_3]$ cat file.txt.backup
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
hello world !!!!
end
[lingyun@localhost open_3]$