Day 05 - file operation function

The first 05 God - File operation related functions

01.stat function ( a key )

#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>

int stat(const char* path,struct stat *buf)
int lstat(const char *pathname,struct stat *buf)
 function ：
    Get file status information 
   stat and lstat The difference between ：
         When the file is a symbolic link ,lstat What is returned is the information of the symbolic link itself ;
         and stat Returns information about the file specified by the link 
 Parameters ：
   path： file name 
   buf： The structure that holds the file information 
 Return value 
      success ：0;
      Failure ：-1;

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-XdrXSGRQ-1656152623410)(D:\ picture \image-20220625073954397.png)]

Gets file property information

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
int main()
{
    
        int ret=-1;
        struct stat s;
        ret=stat("txt",&s);
        if(ret==-1)
        {
    
                perror("stat");
                return 1;
        }
        printf("st_dev=%lu\n",s.st_dev);
        printf("st_ino=%ld\n",s.st_ino); 
        return 0;
}

st_mode Get the first version of file type and permission

man 2 stat manual

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-RwSiqGLs-1656152623411)(D:\ picture \image-20220625083229032.png)]

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
int show_file_type(struct stat *s)
{
    
        switch(s->st_mode&S_IFMT){
    
                case S_IFBLK:printf("block device Block device \n");break;
                case S_IFCHR:printf("character device Character device \n");break;
                case S_IFDIR:printf("directory Catalog \n");break;
                case S_IFIFO:printf("IS A FIFO The Conduit \n");break;
                case S_IFLNK:printf("IS A symLINK A symbolic link \n");break;
                case S_IFREG:printf("IS A regular file Ordinary documents \n");break;
                case S_IFSOCK:printf("IS A SOCKET\n");break;
        default :printf("unknown\n");break;
        }
   return 0;
}
int main(int argc,char *argv[])
{
    
        struct stat s;
        if(argc!=2)
        {
    
                printf("usage:./a.out filename");
                return 1;
        }
// Get file information 
int ret=-1;
ret=stat(argv[1],&s);
if(ret==-1)
{
    
        perror("stat");
        return 1;
}
// Show file type 
show_file_type(&s);
return 0;
}

Second version

int show_file_type_v2(struct stat *s)
{
    
  if(S_ISREG(s->st_mode))
  {
    
          printf("is a regular file\n");
 return 0;
  }

  if(S_ISLNK(s->st_mode))
  {
    
          printf("is a symblic link\n");
 return 0;
  }

  if(S_ISBLK(s->st_mode))
  {
    
          printf("is a block device\n");
 return 0;
  }
  if(S_ISDIR(s->st_mode))
         printf("is a directory\n");
 return 0;
  }
  if(S_ISCHR(s->st_mode))
  {
    
          printf("is a character devicce\n");
 return 0;
  }

  if(S_ISFIFO(s->st_mode))
  {
    
          printf("is a FIFO\n");
 return 0;
  }
  if(S_ISSOCK(s->st_mode))
  {
    
          printf("is a socket Socket \n");
 return 0;
  }
  return 0;
}

File permissions

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-o7mGUKDC-1656152623413)(D:\ picture \image-20220625093211566.png)]

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-WFyEeQgZ-1656152623414)(D:\ picture \image-20220625093507666.png)]

access function

chmod function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-9hSaHIpB-1656152623415)(D:\ picture \image-20220625094310470.png)]

chown function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-vlX51xUl-1656152623416)(D:\ picture \image-20220625094400639.png)]

truncate function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-gDR1wt97-1656152623416)(D:\ picture \image-20220625094429486.png)]

link function

symlink function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-kIaLHiRa-1656152623417)(D:\ picture \image-20220625094523851.png)]

readlink function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-eO9nPkGk-1656152623418)(D:\ picture \image-20220625094601834.png)]

unlink function

rename function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-h9rrKCYp-1656152623418)(D:\ picture \image-20220625094710678.png)]

02. File descriptor copy

dup function

#include<unistd.h>
int dup(int oldfd);
 function ：
   adopt oldfd Copy out a new file descriptor , The new file descriptor is the smallest available file descriptor in the call process file descriptor table , Final oldfd And the new file descriptor point to the same file 
 Parameters ：
  oldfd： File descriptors that need to be copied  oldfd
 Return value ：
    success ： New file descriptor 
    Failure ：-1;

The book explains ：[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-6sBzldeH-1656152623419)(D:\ picture \image-20220625100258289.png)]

Share one file offset

#include<stdio.h>
#include<stdlib.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<string.h>
#include<unistd.h>
int main()
{
    
        // Open file 
        int fd=-1;
        fd=open("txt",O_RDWR|O_CREAT,0644);
        if(fd==-1)
       {
    
               perror("open");
               return 0;
       }
        // operation 
        int newfd=dup(fd);
        if(newfd==-1)
        {
    
                perror("dup");
        return 0;
        }
        write(fd,"asdfsd",6);
        write(newfd,"12456",5);

        // Close file  
        close(fd);
        close(newfd);
}
                    

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-hO368tFx-1656152623419)(D:\ picture \image-20220625101913209.png)]

dup2 function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-n1TLaZdi-1656152623420)(D:\ picture \image-20220625102931102.png)]

dup2 You can directly complete the above operation

The book explains ：

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-8k1y0cAo-1656152623421)(D:\ picture \image-20220625103108205.png)]

fcnlt function

Copy file descriptors

#include<unistd.h>
#include<fcntl.h>
int fcntl(int fd,int cmd ,.../* arg*/);
 function ： Change the nature of open files ,fcntl Provides control over descriptors .
 Parameters ：
  fd： File descriptor for operation 
  cmd： Mode of operation 
  arg： in the light of cmd Value ,fcntl Can accept the third parameter int arg.
 Return value ：
   success ： Return some other value 
   Failure ：-1

There are five functions ：

1） Copy an existing descriptor （cmd=F_DUPFD）

2） get / Set file descriptor flag （cmd=F_GETFD）

3） get / Set file status flag （cmd=F_GETFL or F_SETFL）

4） get / Set asynchronous I/O ownership （cmd=F_GETOWN or FSETOWN）

5） get / Set record lock （cmd=F_GETLK,F_SETLK or F_SETLKW）

The book explains ：

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-Zw8RZxFM-1656152623422)(D:\ picture \image-20220625110957038.png)]

getcwd function

#include<unistd.h>

char* getcwd(char *buf,size_t size)
 function ： Get the current process Directory 
 Parameters ：
    buf： Buffer zone , Store the current working directory 
    size： Buffer size 
 Return value ：
 success ：buf Save the current process working directory as the location 
 Failure ：NULL

chdir function

#include<unistd.h>

int chdir(const char*path)
 function ：  Modify the current process 
 Parameters ：
   path： Switched path 
 Return value ：
      success ：0
      Failure ：-1

#include<unistd.h>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main()
{
    
        int ret=-1;
        char buf[128];
        // Get the current path 
        if(NULL==getcwd(buf,128))
        {
    
                perror("getcwd");
                return 1;
        }
        printf("buf:%s",buf);
        // Modify the path 
        ret=chdir("/home/rui");
        if(-1==ret)
        {
    
                perror("chdir");
                return 1;
        }
        // Get the path 
        memset(buf,0,128);
        if(NULL==getcwd(buf,128))
        {
           
          perror("getcwd");
          return 1;
        }
        printf("buf:%s",buf);
return 0;
}

opendir function

closedir function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-r5UWEZ6i-1656152623422)(D:\ picture \image-20220625175011901.png)]

readdir function

[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-uwuddhUr-1656152623422)(D:\ picture \image-20220625181026538.png)]

    }
    // Get the path 
    memset(buf,0,128);
    if(NULL==getcwd(buf,128))
    {       
      perror("getcwd");
      return 1;
    }
    printf("buf:%s",buf);

return 0;
}

#### opendir function 

#### closedir function 

[ Outside the chain picture transfer in ...(img-r5UWEZ6i-1656152623422)]

#### readdir function 

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[ Failed to transfer the external chain picture , The origin station may have anti-theft chain mechanism , It is suggested to save the pictures and upload them directly (img-FaCCjihx-1656152623423)(D:\ picture \image-20220625181919233.png)]