Linux Internship Report - Experiment 4 File I/O Operation

Purpose

1. Familiar with the functions of file descriptors to manipulate files;
2. Master the application of non-blocking file operations;
3. Master the file lock application;
4. Master the operation of directory files and symbolic link files.

content                                

1. At the end of Chapter 5 of the textbook, page 213, questions 1, 2, 3, 4, and 7.

• Design a program that requires to open the file "pass", if there is no such file, create a new file, and set the permissions to only the owner has read-only permissions.

• #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  int main()
  {
      int fd;
      if((fd=open("pass",O_CREAT)<0))
      {
          printf("file is not exist.\n");
      }
      printf("createFile pass,fd:%d\n",fd);
      chmod("pass",S_IRUSR);
      return 0;
  }

  2. Design a program that requires a new file "hello", and use the write function to write the string "C software design under Linux" into the file.

• #include <stdio.h>
  #include <unistd.h>
  #include <stdlib.h>
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <fcntl.h>
  #include <string.h>
  int main()
  {
  	int fd,w;
  	if((fd=open("hello",O_TRUNC|O_WRONLY,0666))<0)
  	{
  		printf("打开文件出错");
  		return 1;
  	}
  	char str[]="Linux下C软件设计";
  	if((w=write(fd,str,sizeof(str)))<0)
  	{
  		printf("写入文件出错");
  		return 1;
  	}
  	close(fd);
  	return 0;
  }
  

  

   3. Design a program that requires the read function to read the system file "/etc/passwd" and display the output in the terminal

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
int main()
{
	int fd,r,w;
	char str[50];
	if((fd=open("/etc/passwd",O_RDONLY))<0)
	{
		printf("读取文件失败！");
		return 1;
	}
	while((r=read(fd,str,50))>0)
	{
		if((w=write(STDOUT_FILENO,str,r))<0)
			printf("写入文件出错");
	}
	close(fd);
	return 0;
}

 Design a program that requires to open the file "pass", if there is no such file, create a new file, read the system file "/etc/passwd", and write the contents of the file into the "pass" file.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
	int fdsrc,fddes,cnt,w;
	char str[30];
	if((fddes=open("pass",O_CREAT|O_TRUNC|O_WRONLY,0600))<0)
	{
		printf("打开文件pass失败！");
		return 1;
	}
	if((fdsrc=open("/etc/passwd",O_RDONLY))<0)
	{
		printf("打开文件失败！");
		return 1;
	}
	while((cnt=read(fdsrc,str,30))>0)
	{
		if((w=write(fddes,str,30))<0)
			printf("写入文件失败");
	}
	close(fdsrc);
	close(fddes);
	return 0;
}

Question: I haven't found out why the file pass keeps failing to open? 

⑦ Design a program that requires to create a soft link "ls1" and a hard link "ls2" for the "/bin/ls" file, and view the two link files and the "/bin/ls" file.

#include <stdlib.h>
#include <unistd.h>
int main()
{
	symlink("/bin/ls","ls1");
	link("/bin/ls","ls2");
	system("ls -l /bin/ls");
	system("ls -l ls1");
	system("ls -l ls2");
	return 0;
}

1. Programmatically implement the basic functions of ls and implement the -l parameter function; such as:
   1. If no parameter is specified, all visible files in the current directory are displayed;
   2. If a parameter is specified, the parameter specifies the file to display the file information, and if it is a directory, the file information in the directory is displayed;
   3. The -l parameter format is the same as ls -l;
   4. The specified parameter can be multiple;

      #include<stdio.h>
      #include<unistd.h>
      #include<stdlib.h>
      #include<sys/types.h>
      #include<sys/stat.h>
      #include<string.h>
      #include<time.h>
      #include<pwd.h>
      #include<grp.h>
      void filebuf(mode_t mode,char *rs){ //判断文件类型以及所有者，组和其他的权限；
      	if(S_ISDIR(mode)){
      		rs[0]='d';
      	}
      	else if(S_ISREG(mode)){
              rs[0]='-';
      	}
      	else if(S_ISFIFO(mode)){
              rs[0]='p';
      	}
      	else if(S_ISLNK(mode)){
      		rs[0]='l';
      	}
      	else if(S_ISBLK(mode)){
      		rs[0]='b';
      	}
      	else if(S_ISSOCK(mode)){
      		rs[0]='s';
      	}
      	else if(S_ISCHR(mode)){
      		rs[0]='c';
      	}
          if(mode & S_IRUSR)  rs[1]='r';
          else rs[1]='-';
          if(mode & S_IWUSR)  rs[2]='w';
          else rs[2]='-';
          if(mode & S_IXUSR)  rs[3]='x';
          else rs[3]='-';
          if(mode & S_IRGRP)  rs[4]='r';
          else rs[4]='-';
          if(mode & S_IWGRP)  rs[5]='w';
          else rs[5]='-';
          if(mode & S_IXGRP)  rs[6]='x';
          else rs[6]='-';
          if(mode & S_IROTH)  rs[7]='r';
          else rs[7]='-';
          if(mode & S_IWOTH)  rs[8]='w';
          else rs[8]='-';
          if(mode & S_IXOTH)  rs[9]='x';
          else rs[9]='-';
          rs[10]='\0';
      }
      int main(int argc, char *argv[]) {
      	struct stat fst;
      	struct tm *mytime=(struct tm *)malloc(sizeof(struct tm));
      	char rs[12];
      	if(argc!2){
              fprintf(stderr,"Usage: %s <pathname>\n",argv[0]);
              exit(EXIT_FAILURE);
      	}
      	if(stat(argv[1],&fst)==-1)
          {
              perror("stat");
              exit(EXIT_FAILURE);
          }
          filebuf(fst.st_mode,rs);
          printf("%s",rs); //输出文件类型与权限信息；
          printf(" %d",fst.st_nlink);//输出文件的硬链接数；
          printf(" %s",getpwuid(fst.st_uid)->pw_name);//输出所属用户名；
          printf(" %s",getgrgid(fst.st_gid)->gr_name);//输出用户所在组;
          printf(" %1d",fst.st_size);//输出文件大小；
          mytime=localtime(&fst.st_mtime);//获取文件修改时间；
          printf("%d-%02d-%02d%02d:%02d",mytime->tm_year+1900,mytime->
      tm_mon+1,mytime->tm_mday,mytime->tm_hour,mytime->tm_min);
          printf(" %s",argv[1]);//输出文件名；
          printf("\n");
          return 0;
      }