How to read a certain range of lines using systems calls - c++

Question

I am up a wall on an assignment that I have been hacking at for several days. Basically I need to make an executable program using C/C++ to take 3 queries from the user m,n and a file name.
The program will then output the text on those lines to the terminal. I must use read(), write(), open() and close() system calls to do it.
My approach is to go char by char (slow I know but everything else I tried seems to give segementation faults).
But it doesn't seem to work properly. When I use smaller parameters it just prints the whole thing, but if I use bigger parameters it doesn't print anything at all.
Can anyone tell me where I'm going wrong?
// Task 2 of Lab 3
#include<unistd.h> // required library for the system calls
#include<fcntl.h> // required for system calls usage
#include <stdlib.h> // required for the use of exit statement, and atoi
#include<stdio.h> // required for the use of perror
#include<string>
using namespace std;
int main(int argc,char *argv[]){
int m = atoi(argv[1]);
int n = atoi(argv[2]); // taking commmand line args by conversion with atoi
int file; // integer value for holding the file descriptor
ssize_t display;
char *buff[1];
int currentLine = 0;
// open the first file for reading
file = open(argv[3],O_RDONLY);
if(file == -1 ){ // error handler for system call 1: open()
perror("Did not open, exiting...");
exit (1);
}
while(((display = read(file,buff,1)) > 0)){
if(*buff[0] == '\n'){
currentLine++;
}
if((currentLine >= m) && (currentLine <= n)){
if(write(STDOUT_FILENO, buff,display) != display){ // if statement doubles as error handling for read()
perror("Problem with writing..."); // errror handling for write()
exit(-1);
}
}
else{
}
}
file = close(file); // Final system call close()
return 0;
}
Sample testfile:
I have some information in here.
Each line should print to the screen
3 lines total
make that 4
Wait? WHAT! I need 12 minimum???
Hm....
Wellp better start typing then. Let's see what can I write about?
Midterms are coming
They scare me
I hate exams, but I love code
woah i also need numbers in here uh 23
19 and lets do 100 and 400 just to add a couple more
maybe i should go ahead and add a 903 here
300
and that previous 300 got it's own line
with this file ...
I have a good mix of chars,numbers, and symbols
that's good enough
time to test!