示例：集成文件系统 C 函数

该程序将执行下列操作：

1

使用 getuid() 函数来确定实用户标识 (uid)。

2

使用 getcwd() 函数来确定当前目录。

3

使用 open() 函数来创建文件。它将为所有者（创建该文件的人员）建立对于该文件的读、写和执行权限。

4

使用 write() 函数将字节字符串写入文件。在打开操作 (3) 中所提供的文件描述符用于标识文件。

5

使用 close() 函数来关闭文件。

6

使用 mkdir() 函数在当前目录中创建新的子目录。为所有者给定了对于该子目录的读、写和执行访问权。

7

使用 chdir() 函数将新的子目录更改为当前目录。

8

使用 link() 函数来创建指向先前所创建的文件 (3) 的链接。

9

使用 open() 函数来打开文件以执行只读操作。通过在 (8) 中所创建的链接可访问该文件。

10

使用 read() 函数从文件中读取字节字符串。在打开操作 (9) 中所提供的文件描述符用于标识文件。

11

使用 close() 函数来关闭文件。

12

使用 unlink() 函数来除去指向该文件的链接。

13

使用 chdir() 函数将当前目录更改回在其中创建新的子目录的父目录。

14

使用 rmdir() 函数来除去先前所创建的子目录 (6)。

15

使用 unlink() 函数来除去先前所创建的文件 (3)。

 
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
 
 
#define BUFFER_SIZE       2048
#define NEW_DIRECTORY     "testdir"
#define TEST_FILE         "test.file"
#define TEST_DATA         "Hello World!"
#define USER_ID           "user_id_"
#define PARENT_DIRECTORY  ".."
 
 
char  InitialFile[BUFFER_SIZE];
char  LinkName[BUFFER_SIZE];
char  InitialDirectory[BUFFER_SIZE] = ".";
char  Buffer[32];
int   FilDes = -1;
int   BytesRead;
int   BytesWritten;
uid_t UserID;
 
 
void CleanUpOnError(int level)
{
   printf("Error encountered, cleaning up.\n");
   switch ( level )
      {
       case 1:
           printf("Could not get current working directory.\n");
           break;
       case 2:
           printf("Could not create file %s.\n",TEST_FILE);
           break;
       case 3:
           printf("Could not write to file %s.\n",TEST_FILE);
           close(FilDes);
           unlink(TEST_FILE);
           break;
       case 4:
           printf("Could not close file %s.\n",TEST_FILE);
           close(FilDes);
           unlink(TEST_FILE);
           break;
       case 5:
           printf("Could not make directory %s.\n",NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 6:
           printf("Could not change to directory %s.\n",NEW_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 7:
           printf("Could not create link %s to %s.\n",LinkName,InitialFile);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 8:
           printf("Could not open link %s.\n",LinkName);
           unlink(LinkName);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 9:
           printf("Could not read link %s.\n",LinkName);
           close(FilDes);
           unlink(LinkName);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 10:
           printf("Could not close link %s.\n",LinkName);
           close(FilDes);
           unlink(LinkName);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 11:
           printf("Could not unlink link %s.\n",LinkName);
           unlink(LinkName);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 12:
           printf("Could not change to directory %s.\n",PARENT_DIRECTORY);
           chdir(PARENT_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 13:
           printf("Could not remove directory %s.\n",NEW_DIRECTORY);
           rmdir(NEW_DIRECTORY);
           unlink(TEST_FILE);
           break;
       case 14:
           printf("Could not unlink file %s.\n",TEST_FILE);
           unlink(TEST_FILE);
           break;
       default:
           break;
      }
   printf("Program ended with Error.\n"\
          "All test files and directories may not have been removed.\n");
}
 
int main ()
{
 1
/* Get and print the real user id with the getuid() function. */
   UserID = getuid();
   printf("The real user id is %u. \n",UserID);
 
 2
/* Get the current working directory and store it in InitialDirectory. */
   if ( NULL == getcwd(InitialDirectory,BUFFER_SIZE) )
      {
      perror("getcwd Error");
      CleanUpOnError(1);
      return 0;
      }
   printf("The current working directory is %s. \n",InitialDirectory);
 
 3
/* Create the file TEST_FILE for writing, if it does not exist.
   Give the owner authority to read, write, and execute. */
   FilDes = open(TEST_FILE, O_WRONLY | O_CREAT | O_EXCL, S_IRWXU);
   if ( -1 == FilDes )
      {
      perror("open Error");
      CleanUpOnError(2);
      return 0;
      }
   printf("Created %s in directory %s.\n",TEST_FILE,InitialDirectory);
 
 4
/* Write TEST_DATA to TEST_FILE via FilDes */
   BytesWritten = write(FilDes,TEST_DATA,strlen(TEST_DATA));
   if ( -1 == BytesWritten )
      {
      perror("write Error");
      CleanUpOnError(3);
      return 0;
      }
   printf("Wrote %s to file %s.\n",TEST_DATA,TEST_FILE);
 
 5
/* Close TEST_FILE via FilDes */
   if ( -1 == close(FilDes) )
      {
      perror("close Error");
      CleanUpOnError(4);
      return 0;
      }
   FilDes = -1;
   printf("File %s closed.\n",TEST_FILE);
 
 6
/* Make a new directory in the current working directory and
   grant the owner read, write and execute authority */
   if ( -1 == mkdir(NEW_DIRECTORY, S_IRWXU) )
      {
      perror("mkdir Error");
      CleanUpOnError(5);
      return 0;
      }
   printf("Created directory %s in directory %s.\n",NEW_DIRECTORY,InitialDirectory);
 
 7
/* Change the current working directory to the
   directory NEW_DIRECTORY just created. */
   if ( -1 == chdir(NEW_DIRECTORY) )
      {
      perror("chdir Error");
      CleanUpOnError(6);
      return 0;
      }
   printf("Changed to directory %s/%s.\n",InitialDirectory,NEW_DIRECTORY);
 
/* Copy PARENT_DIRECTORY to InitialFile and
   append  "/" and TEST_FILE to InitialFile. */
   strcpy(InitialFile,PARENT_DIRECTORY);
   strcat(InitialFile,"/");
   strcat(InitialFile,TEST_FILE);
 
/* Copy USER_ID to LinkName then append the
   UserID as a string to LinkName. */
   strcpy(LinkName, USER_ID);
   sprintf(Buffer, "%d\0", (int)UserID);
   strcat(LinkName, Buffer);
 
 8
/* Create a link to the InitialFile name with the LinkName. */
   if ( -1 == link(InitialFile,LinkName) )
      {
      perror("link Error");
      CleanUpOnError(7);
      return 0;
      }
   printf("Created a link %s to %s.\n",LinkName,InitialFile);
 
 9
/* Open the LinkName file for reading only. */
   if ( -1 == (FilDes = open(LinkName,O_RDONLY)) )
      {
      perror("open Error");
      CleanUpOnError(8);
      return 0;
      }
   printf("Opened %s for reading.\n",LinkName);
 
 10
/* Read from the LinkName file, via FilDes, into Buffer. */
   BytesRead = read(FilDes,Buffer,sizeof(Buffer));
   if ( -1 == BytesRead )
      {
      perror("read Error");
      CleanUpOnError(9);
      return 0;
      }
   printf("Read %s from %s.\n",Buffer,LinkName);
   if ( BytesRead != BytesWritten )
      {
      printf("WARNING: the number of bytes read is "\
             "not equal to the number of bytes written.\n");
      }
 
 11
/* Close the LinkName file via FilDes. */
   if ( -1 == close(FilDes) )
      {
      perror("close Error");
      CleanUpOnError(10);
      return 0;
      }
   FilDes = -1;
   printf("Closed %s.\n",LinkName);
 
 12
/* Unlink the LinkName link to InitialFile. */
   if ( -1 == unlink(LinkName) )
      {
      perror("unlink Error");
      CleanUpOnError(11);
      return 0;
      }
   printf("%s is unlinked.\n",LinkName);
 
 13
/* Change the current working directory
   back to the starting directory. */
   if ( -1 == chdir(PARENT_DIRECTORY) )
      {
      perror("chdir Error");
      CleanUpOnError(12);
      return 0;
      }
   printf("changing directory to %s.\n",InitialDirectory);
 
 14
/* Remove the directory NEW_DIRECTORY */
   if ( -1 == rmdir(NEW_DIRECTORY) )
      {
      perror("rmdir Error");
      CleanUpOnError(13);
      return 0;
      }
   printf("Removing directory %s.\n",NEW_DIRECTORY);
 
 15
/* Unlink the file TEST_FILE */
   if ( -1 == unlink(TEST_FILE) )
      {
      perror("unlink Error");
      CleanUpOnError(14);
      return 0;
      }
   printf("Unlinking file %s.\n",TEST_FILE);
 
 
   printf("Program completed successfully.\n");
   return 0;
}