copying data from file to anothr file

[CD4]

hello i am a newbie.. i had been following Beginning linux programming 4th edition. I tried to go for a sample but the data isnt getting copied to other file but the new file files.in is formed

#include<unistd.h>
#include<stdlib.h>
#include<fcntl.h>
#include<sys/types.h> 
#include<stdio.h>

int main() {
char buff[]="Hello world! This is CodeZer0.I love using linux specially BackTrack4.I am concentrating on c programming\n";
char block[10];
int op,in;
int rdbyte;
 op=open("files.out1",O_RDWR|O_CREAT,S_IRUSR|S_IWUSR);
 write(op,buff,sizeof(buff));
  if (op==-1)
   write(1,"some error\n",11);
 in=open("files.in",O_RDWR|O_CREAT,S_IRUSR|S_IWUSR);
  if (in==-1)
   write(1,"some error in files.in\n",23);
 while((rdbyte=read(op,block,sizeof(block)))>0);
 write(in,block,rdbyte);
return 0;
}

please help..thanks in advance

[Duthomhas]

Line 19 has a stray semicolon.

[CD4]

well thanks for pointing out (;) mistake but still files.in is empty.the data from files.out1 hasn't been copied to it.please help

[Duthomhas]

It is because your file handling is scrambled.

Line 12: you open a file for writing
Line 13: you write some stuff to it
Line 14: you check to see whether the file opened properly (non sequitur)

Line 19: you try to read stuff from the output file (that you just created and left the file pointer at the end of it)


Try putting a lseek(op,0,SEEK_SET); before line 19 and see what that does.
You might also want to swap lines 13 and 14.

Hope this helps.

[CD4]

hello duoas.. i am a coplete newbie so its not getting clear.. i re-wrote the program with many changes where the eror was taking place.. can you explain abit more on wats the problem..

#include<unistd.h>
#include<stdlib.h>
#include<fcntl.h>
#include<sys/types.h> 
#include<stdio.h>

int main() {
char block[106];
int op,in;
int rdbyte;
 op=open("files.out1",O_RDWR|O_CREAT,S_IRUSR|S_IWUSR|S_IXUSR|S_IROTH|S_IWOTH|S_IXOTH);
   if (op==-1)
   write(1,"some error\n",11);
 rdbyte=write(op,"Hello world! This is CodeZer0.I love using linux specially BackTrack4.I am concentrating on c programming\n",106);
 if (rdbyte==0)
  write(1,"data not written\n",17);

 in=open("files.in",O_RDWR|O_CREAT,S_IRUSR|S_IWUSR|S_IXUSR|S_IROTH|S_IWOTH|S_IXOTH);
  if (in==-1)
   write(1,"some error in files.in\n",23);
 printf("%d\n",op);
 rdbyte=read(op,block,106);
 if (rdbyte==0)
  write(1,"data not read\n",14);
 if (rdbyte==-1)
  write(1,"some error\n",11);
 rdbyte=write(in,block,106);
 if  (rdbyte==0);
  write(1,"data not entered\n",17);
 if (rdbyte==-1)
  write(1,"some error2\n",15);

return 0;
}

shell output::

# ./cp
3
data not read
data not entered