Question

I need to read in a file, then print it out to STDOUT but double spaced. What I have so far is:

#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#define BUFSZ 1024

int main(int argc, char* argv[]){

int n, fdin;
char buf[BUFSZ];

if ((fdin=open(argv[1],O_RDONLY))<0){
  perror(argv[1]);
  exit(-1);
}
while(( n = read(fdin, buf, BUFSZ))>0){
 if(write(STDOUT_FILENO,buf,n) != n){
  fprintf(stderr, "Write Error\n");
  exit(-1);
 }
 printf("\n");
}
close(fdin);
return(0);
}

I’m new to C and don’t know how I could implement the \n into the code, my printf(“\n”) is useless in trying to double space the entire file’s contents. I think I have to add the \n into the read? But I’m not entirely sure if that’s correct or how to do it.

Answer 1

read() does not stop reading when it encounters a new-line character so the algorithm in the posted code could easily miss writing a blank line as the read() could read more than one line.

A simpler approach would use fgets():

FILE* f = fopen(argv[1], "r");
if (f)
{
    char buf[BUFSZ];
    while (fgets(buf, BUFSZ, f))
    {
        printf("%s", buf);

        /* fgets() may not have read a full line if the
           length of the line was greater than BUFSZ,
           so check it did before double spacing. */
        if (strrchr(buf, '\n')) printf("\n");
    }
    fclose(f);
}