File I/O operations file Open, create, close and locate-based on Linux system file IO

1.

Open File

#include <sys/types.h>#include<sys/stat.h>#include<fcntl.h>int Open (constchar *pathname,int flag);    // Open an existing file int Open (constchar *pathname,int flags,mode_t mode);   // If the file does not exist, create it first // Success Returns the file description pair, otherwise returns-1 // pathname is the relative or absolute pathname of the file

The file descriptor starts at 3 (0,1,2 is occupied by standard IO) and is assigned to the open file in turn

Flags value:

o_rdonly;   Read-only o_wronly;　　Write only o_rdwr; Read and write O_creat;o_excl;o_noctty;o_trung;o_append;o_nonbolck;o_nonelay;o_sync;

Mode take value

S_isuid; S_isgid; S_SVTX; S_IRUSR; S_IWUSR; S_IXUSR; S_IRGRP; S_IWGRP; S_IXGRP; S_iroth; S_iwoth; S_ixoth;

Combination mode

S_irwxu; S_IRWXG; S_irwxo;

Example:

Open File

1#include <sys/types.h>2#include <sys/stat.h>3#include <fcntl.h>4 5#include <stdio.h>6#include <stdlib.h>7#include <string.h>8 9 #defineFLAGS o_wronly| O_creat| O_truncTen #defineMODES s_irwxu| s_ixgrp| s_irgrp| s_iroth| S_ixoth One  A intMainvoid) - { -     Const Char*pathname; the     intFD; -     Charpn[ -]; -printf"Please input the pathname <30 strings:\n"); -scanf"%s", PN); +Pathname=PN; -     if((Fd=open (pathname,flags,modes)) ==-1) +     { Aprintf"error can ' t open file! \ n"); atExit255); -     } -printf"OK, file has been open!\n"); -printf"fd=%d\n", FD); -     return 0; -}

2.

Create a file

#include <sys/types.h>#include<sys/stat.h>#include<fcntl.h>int creat (constchar *pathname,mode_t mode);

If successful, returns a file descriptor opened as write-only, otherwise 1

Note: creat is equivalent to

Open (pathname,o_wronly| O_creat| O_trunc,mode);

New ways to create files and open them

Open (pathname,o_rdwr| O_creat| O_trunc,mode);

3.

Close File

#include <unistd.h>int close (int fd);

FD is a file descriptor, successfully returned 0, error returned-1

4.

Locating files

#include <sys/types.h>#include<unistd.h>off_t lseek (int fd,off_t offset, int whence);

The displacement magnitude of the position at offset, which is related to the whence parameter

Seek_set;   // displacement is the offset byte at the beginning of the file. Seek_cur;   // offset byte from current position Seek_end;   // offset byte from end of file

The latter two parameters allow offset negative values

You can use this method to get the current amount of file displacement

off_t offset;offset=lseek (FD,0, seek_cur);

You can also use this method to test whether a file can be set at an offset

File I/O operations file Open, create, close and locate-based on Linux system file IO