Use of file i/o in C

C Documents in I/O There are several functions that we need to know , Yes open function ,read function ,write function , as well as close function .

open Use of functions

open:
	 Open a file 
	NAME
       open, openat, creat - open and possibly create a file

SYNOPSIS
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>

       int open(const char *pathname, int flags);

	   pathname： Pathname / file name ( Not in the current directory , Path required )// Is all paths ？
	   flags： Document mark , Indicates the read-write permission of the file 
	   O_RDONLY  read-only 
	   O_WRONLY  Just write 
	   O_RDWR  	 Can read but write 
	   
	    Return value : Successfully returned a new file descriptor 
			 Failure to return -1, meanwhile error Set up 
			

close Use of functions

close:
	 Close a file 
	NAME
       close - close a file descriptor

SYNOPSIS
       #include <unistd.h>

       int close(int fd);
		fd： File descriptor , The file we opened 

read Use of functions

read:
	 Read from file 
	NAME
       read - read from a file descriptor

SYNOPSIS
       #include <unistd.h>

       ssize_t read(int fd, void *buf, size_t count);
		fd： File descriptor , The file we opened 
		buf: Where we will store the content we read 
		count： How many bytes to read 
		
		 Return value : Successfully returned the number of bytes read ( return 0 Hour means that the document has been read )
				 Failure to return -1, meanwhile error Set up 

write Use of functions

write:
	 Write content to file 
	NAME
       write - write to a file descriptor

SYNOPSIS
       #include <unistd.h>

       ssize_t write(int fd, const void *buf, size_t count);

	   fd： File descriptor , The file we opened 
	   buf:  What we want to write 
	   count:  How many bytes to write 
	   
	    Return value ： Successfully returned the number of bytes written ( return 0, The representative didn't write it in )
				 Failure to return -1, meanwhile error Set up 

When we use system files , It is necessary to pay attention to the use of the specified header files , Use the functions in the header file to complete the functions we want .

practice ：
Through the call of system functions, the things in a function , Write it into another function .

#include <sys/types.h>
#include <sys/stat.h>
#include<stdio.h>
#include <fcntl.h>
int main()
{
    
    int fd = open("nice.c",O_RDWR); 
    int fd2=open("cp1.c",O_RDWR);
    char buf[5000]={
    0};// There is actually a flaw here , This is a waste of space .
    while(1)
    {
    
        int read1;
       read1= read(fd,buf,1);
        write(fd2,buf,1);
        if(read1==0)
        {
    
            close(fd2);
            close(fd);
            break;
        }
    }
    return 0;
}

Last , Let's summarize , Is actually through the system I/O To operate files is actually to operate fd File operators .