You have to use program with two arguments, the file names copy_from copy_to.
There is an access function with which we can see whether the file exists or not
access(filename,F_OK);
open 1. parameter= file name
open 2. parameter for what we want to use the file
O_RDONLY=only for reading,O_WRONLY-only for writing
There is errno variable in which there is the number of error --
if (errno!=0) there is an error
The three parameter long version of open - it can create the file if it doesnt exist
there is a creat function as well - creat(filename,permissions);
O_TRUNC = if it existed, clear the content,
O_CREAT=create if it doesn't exist
3. parameter the permission, if it has to be created
S_IRUSR=permission for reading by the owner e.g.
Read gives back the number of bytes
1. parameter the file descriptor
2. parameter the address of variable, we read into
3. parameter the number of bytes we want to read in
Write gives back the number of written bytes
1. parameter the file descriptor
2. parameter the address of variable we want to write out
3. parameter the number of bytes we want to write out
//make a copy of file given in argv[1] to file given in argv[2]
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h> //open,creat
#include <sys/types.h> //open
#include <sys/stat.h>
#include <errno.h> //perror, errno
int main(int argc,char** argv){
if (argc!=3){perror("You have to use program with two arguments, the file names copy_from copy_to");exit(1);}
int f,g;
f=open(argv[1],O_RDONLY);
//there is an access function with which we can see whether the file exists or not
//access(filename,F_OK);
//open 1. parameter= file name
//open 2. parameter for what we want to use the file
//O_RDONLY=only for reading,O_WRONLY-only for writing
if (f<0){ perror("Error at opening the file\n");exit(1);}
//There is errno variable in which there is the number of error --
//if (errno!=0) there is an error
g=open(argv[2],O_WRONLY|O_CREAT|O_TRUNC,S_IRUSR|S_IWUSR);
//the three parameter long version of open - it can create the file if it doesnt exist
//there is a creat function as well - creat(filename,permissions);
//O_TRUNC = if it existed, clear the content,
//O_CREAT=create if it doesn't exist
//3. parameter the permission, if it has to be created
//S_IRUSR=permission for reading by the owner e.g.
if (g<0){ perror("Error at opening the file\n");exit(1);}
char c;
while (read(f,&c,sizeof(c))){
//read gives back the number of bytes
//1. parameter the file descriptor
//2. parameter the address of variable, we read into
//3. parameter the number of bytes we want to read in
printf("%c",c); //we prints out the content of the file on the screen
if (write(g,&c,sizeof(c))!=sizeof(c))
{perror("There is a mistake in writing\n");exit(1);}
//write gives back the number of written bytes
//1. parameter the file descriptor
//2. parameter the address of variable we want to write out
//3. parameter the number of bytes we want to write out
}
close(f);
close(g);
return 0;
}
