Thread: new line character being added while using write system call

Hi ,

I have two files . One source and other destination.

Below are the contents

1302 [12:09] [/cprogs/files] -> cat temp
jimmy
1302 [12:09] [xrakant/cprogs/files] -> cat test
jhony jhony yes papa


I am just copining them using the below code.

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <curses.h>

int main(int argc,char *argv[])
{
     int sfd,dfd,n = 0;
    char buf[5];

    memset(buf,0,sizeof(buf));

    printf("The file name to opened %s \n",argv[1]);
    printf("The file name to copied %s \n",argv[2]);



    if (argc == 4 && !strcmp(argv[1],"-f"))
    {
        printf("need to override the file\n");
    }


    if (argc == 4 && !strcmp(argv[1],"-f"))
    {
         printf("need to override the file  1:%s 2:%s 3:%s\n",argv[1],argv[2],argv[3]);

         sfd = open(argv[2],O_RDONLY);
         dfd = open(argv[3],O_WRONLY | O_CREAT | O_TRUNC);
         printf("The open sfd: %d \n",sfd);
         printf("The open sfd: %d \n",dfd);
    }
    else
    {
         sfd = open(argv[1],O_RDONLY);
         dfd = open(argv[2],O_WRONLY | O_CREAT);
         printf("The open sfd: %d \n",sfd);
         printf("The open sfd: %d \n",dfd);
    }

    while( (n = read(sfd,buf,sizeof(buf))) && (dfd > 0) && strlen(buf) > 0)
    {
        printf("The content: %s number of bytest :%d \n",buf,n);
        write(dfd,buf,n);
        memset(buf,0,sizeof(buf));
    }

    close(sfd);
    close(dfd);

    return 0;
}

Output:

eselnts1302 [12:08] [xrakant/cprogs/files] -> ./sysprog1_1 temp test
The file name to opened temp
The file name to copied test
The open sfd: 3
The open sfd: 4
The content: jimmy number of bytest :5
The content:
number of bytest :1
eselnts1302 [12:08] [xrakant/cprogs/files] -> cat test
jimmy
jhony yes papa


I am not sure how the new line character is being added while doing write to destination file.





Thanks
vlrk

The source file contains "jimmy\n".
Your read is in a loop.
The first pass reads "jimmy".
The second pass reads "\n".
Both are written to the destination file.

I am doing echo "jimmy" > temp to fill the source file.

I am not sure here how \n is being inserted .

Is there any editor where I can see all the special character like \n and other. So that I can be sure that \n is coming from source file.

echo adds a newline.
echo -n supresses it.
cat -E shows end-of-line character as $.
Clearly there's a newline at the end of the file since when you cat the file your prompt appears on the next line. If there weren't a newline your prompt would appear on the same line.
(This is all assuming linux.)

Thanks .. It did worked.