Linux system programming File IO

1. Opening the file's function open, the first parameter represents the file path name, the second is the open tag, and the third one is the file permission

Code:

#include <sys/types.h><sys/stat.h><fcntl.h>#include<stdio.h> int Main () {        int  fd;         = Open ("testopen1", O_creat,0777);        printf ("fd =%d\n", FD);         return 0 ;}

Effect test: Print Open File Returns a descriptor of 3 while creating a file Testopen1

2. Create file functions creat and close functions close

Using code

#include <fcntl.h>#include<stdio.h>#include<unistd.h>#include<stdlib.h>intMainintargcChar*argv[]) {        intFD; if(ARGC <2) {printf ("Please run./app filename\n"); Exit (1); } FD= Creat (argv[1],0777); printf ("FD =%d\n", FD);        Close (FD); return 0;}

Test results:

3. Write the file function write, the first parameter represents the descriptor of the file to be written, the second parameter represents the first memory address of the content to be written, and the third parameter represents the number of bytes to write to the content;

Write successfully returns the number of bytes written, failure returns-1

Test code:

#include <sys/types.h>#include<sys/stat.h>#include<fcntl.h>#include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<string.h>intMainintargcChar*argv[]) {        intFD; if(ARGC <2) {printf ("Please run./app filename\n"); Exit (1); } FD= Open (argv[1],o_creat | O_RDWR,0777); if(FD = =-1) {printf ("Open File failed!"); Exit (0); }        Char*con ="Hello world!"; intnum =Write (Fd,con,strlen (con)); printf ("write%d byte to%s", num,argv[1]);        Close (FD); return 0;}

Result: Hello world! Write Hello file successfully

View the maximum number of open files in the current system

4. Reading the file read, the first parameter is the file descriptor, the second parameter is the memory to read the file contents of the first address, the third parameter is the number of bytes read at a time

Test code, complete file copy

#include <sys/types.h>#include<sys/stat.h>#include<fcntl.h>#include<stdio.h>#include<unistd.h>#include<stdlib.h>#include<string.h>intMainintargcChar*argv[]) {        intFd_src,fd_des; Charbuf[1024x768]; if(ARGC <3) {printf ("Please run./app srcfilename desfilename\n"); Exit (1); } fd_src= Open (argv[1],o_rdonly); Fd_des= Open (argv[2],o_creat | o_wronly | O_trunc,0777); if(Fd_src! =-1&& Fd_des! =-1)        {                intLen =0;  while(len = Read (Fd_src,buf,sizeof(BUF)))                {Write (Fd_des,buf,len);                } close (FD_SRC);        Close (fd_des); }        return 0; }

Effect view, visible to achieve a copy of the file open.c

Linux system programming File IO