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《C 程序设计语言》第八章 fsize 读取文件夹内容例子的讨论

2016-08-30 23:05 274 查看

阅读“C程序设计语言”第八章有一个例子，在UNIX系统中自己实现文件夹内容的读取等各种操作。

其中有一个函数readdir 中利用了open 和read函数来读取文件夹，可是我在Centos7 上总是到失败。

查看stackoverflow上有类似的讨论
http://stackoverflow.com/questions/21405048/linux-open-directory-as-a-file
作者做了这个实验，open是可以打开文件夹但是不能调用读取read，总是返回-1

#include <fcntl.h>
#include <stdio.h>
#include <errno.h>

int main(int argc, char* argv[]) {
int fd = -1;
if (argc!=1) fd=open(argv[1],O_RDONLY,0);
else fd=open(".",O_RDONLY,0);
if (fd < 0){
perror("file open");
printf("error on open = %d", errno);
return -1;
}
printf("file descriptor is %d\n", fd);

char buf[1024];
int n;
if ((n=read(fd,buf,1024))>0){
write(1,buf,n);
}
else {
printf("n = %d\n", n);
if (n < 0) {
printf("read failure %d\n", errno);
perror("cannot read");
}
}
close (fd);
return 0;
}

运行结果

file descriptor is 3
n = -1
read failure 21
cannot read: Is a directory

最佳解释如下

1down
voteaccepted

Files are also called

regular
files

to distinguish them from

special
files

.

Directory or not a

regular
file

. The most common

special
file

is the directory. The layout of a directory file is defined by the filesystem used.

So use opendir to open diretory.

文件分为普通文件和特殊文件。而Directory可以是普通文件也可以不是。取决于具体的文件系统。所以才会定义一套通用的接口 opendir readdir 和closedir

而自己去实现readdir的话设计到具体的文件系统。所以就不深入讨论了。

1down
voteaccepted

Files are also called

regular
files

to distinguish them from

special
files

.

Directory or not a

regular
file

. The most common

special
file

is the directory. The layout of a directory file is defined by the filesystem used.

So use opendir to open diretory.

一个UNIX系统下的使用opendir readdir closedir的例子

#include<stdio.h>
#include<dirent.h>

int main(int argc,char* agrv[]){
DIR* dp;
struct dirent* dirp;

if(argc!=2){
printf("usage:lsdirectory_name\n");
//不返回的话，程序会执行出错
return 0;
}
if((dp=opendir(agrv[1]))==NULL){
printf("cannotopen%s",agrv[1]);
//不返回的话，程序会执行出错
return 0;
}
while((dirp=readdir(dp))!=NULL){
printf("%s\n",dirp->d_name);
}
closedir(dp);
//c语言以非0为真，所以程序执行成功的话返回1，执行失败返回0
return 1;
}

1down
voteaccepted

Files are also called

regular
files

to distinguish them from

special
files

.

Directory or not a

regular
file

. The most common

special
file

is the directory. The layout of a directory file is defined by the filesystem used.

So use opendir to open diretory.

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《C 程序设计语言》 第八章 fsize 读取文件夹内容例子的讨论

《C 程序设计语言》第八章 fsize 读取文件夹内容例子的讨论