Get_Next_Line

This project intends to mimic the functionality of getline, which reads the line from a source then outputs it. The purpose of this project was to understand how memory works.

There are some difference between getline and get_next_line. getline(3) function uses fopen(3) because it givesFILE* stream. However, get_next_line uses open(2) because it gives a file descriptor, and the project requires file descriptor.

FILE* can be converted into a file descriptor using fileno(3). But the opposite is not possible.

Features

This program reads multiple different files and keeps track of where each file finished reading when a new line occurs.

Return Values of get_next_line

get_next_line returns -1, 0, or 1.

Returns 1 if a line has been read successfuly.
Returns 0 if the program is finished reading the file. This will occur when the last line is read more than once.
Returns -1 if the program was unable to read the file.

Complexity of the project

Reading a file and displaying the output is not too hard. Let's suppose we have a file that looks as shown below:

AB
CD
EF

If the buff_size is set to 3, which is how many characters the program will read each time, then it's easy to create a simple program. Because the program will read `AB\n` 3 bytes and then disaply it. But if the buff size is changed to 6, now the program will display first and second line, instead of disaplying 1 line. Because the project also requires for file to be read succefully an only show 1 line at a time, no matter what the buff_size is, extra characters that are read had to be stored.

Installation - Setting up environment

To compile, open libft folder and then type the following commands:

make fclean
make re
make clean

make fclean will remove the libft.a static library. make re wil recompile the library to create .o and static library. make clean will remove the .o files leaving the folder with .c and libft.a static library. This is important because operating systems have different architecture, so the static library has to be created again.

Running the program

There are three different main files that can be used one at a time to test the program. main_1file.c can be replaced with main_2files.c to run the program with 2 files.

gcc get_next_line.c main_1file.c -I. ./libft/libft.a
./a.out

To run the program with command line interface, where the user can enter the file name, use the following commands.

gcc get_next_line.c main_cli.c -I. ./libft/libft.a
./a.out "file_name.txt"

Optional Installation - Valgrind

To check for memory leaks, valgrind can be installed if it is already not installed on the system. Following commands install valgrind on linux and runs the program to check for memory leaks:

sudo apt-get install valgrind
gcc get_next_line.c main_2files.c -I. ./libft/libft.a
valgrind ./a.out

Why is it important to check for memory leaks?

Memory is allocated to manipulate the string. Memory allocation takes place at the heap level several times when following functions are called: ft_strjoin(), ft_strsub(), ft_strdup(), and strjoin_swap() because all 4 of these functions use malloc(). If memory is allocated then once the process is completed, memory has to be deallocated using free(), so system knows that memory is free to be used for something else.

Examples.

Program reads from two files.

Program running through command line interface.

Above are the snapshots of the program when it reads from valid files. First four lines return 1, containing the text it read from the file, but the last line returns 0 because the program finised reading the file.

Program returns -1 because the file is invalid.

mohammadbutt/42_get_next_line