dog

Cat Improved

Usage

$make
$./dog
$./dog dog.c README.md

The problem with cats

One of the most useful commands is cat. You can use it as a discussion simulator if you have no one to talk to.

$cat
Hello !
Hello !
I love you
I love you
^D

However, this command is not suited for writing a poem.

$cat
Il dort. Quoique le sort fût pour lui bien étrange,
Il dort. Quoique le sort fût pour lui bien étrange,
Il vivait. Il mourut quand il n'eut plus son ange;
Il vivait. Il mourut quand il n'eut plus son ange;
La chose simplement d'elle-même arriva,
La chose simplement d'elle-même arriva,
Comme la nuit se fait lorsque le jour s'en va.
Comme la nuit se fait lorsque le jour s'en va.
^D

This isn't cat's only shortcomings. You might want to use cat - half_life3. Obviously, the file half_life3 doesn't exist. However, while you type a love letter in stdin, another user might create the file half_life3 and you won't get an error message. Even if the file half_life3 existed, this other malicious user might modify this file. This is clearly unwanted behaviour.

Man (and woman)'s best friend

The solution to the abovementioned problems is simple. I made a program dog whose behaviour is close to cat. However, dog will load into memory every file it is given before printing them to stdout. You might say that this is a waste of memory, but please keep in mind that on a 64-bits machine, you have access to 16EB of RAM.

dog.c's advantages

If you want to get better at coding in C or PHP, you might want to take a look at dog.c. The code is concise and self-documented. The "single source of truth" paradigm is implemented by putting the entire code in the function main.

Since all of the files contents are stored in memory, memory leaks are a real issue. To avoid this, the best practice is to not allocate any memory. Since dog.c only uses 4 variables, the spatial complexity is O(1). Moreover, there are no control structures. Since there are no while or for, the time complexity is also O(1).

One of the main advantages of writing a program in C is the use of pointers. 'dog.c' make full use of this, and most variables are pointers. Some are even a 'struct' of two pointers. The only regretable exception is argc which does not conform to C's best practices.

This program also uses what we call "quick exit". When using cat with a file that doesn't exists, the program cat takes the time to print an error message before exiting. Because you want to correct your typo as soon as possible, dog will automatically make a segmentation fault if you try to read a non existing file. This way, you can immediately correct your command.

Examples

You can write a poem :

$./dog
Il dort. Quoique le sort fût pour lui bien étrange,
Il vivait. Il mourut quand il n'eut plus son ange;
La chose simplement d'elle-même arriva,
Comme la nuit se fait lorsque le jour s'en va.
^DIl dort. Quoique le sort fût pour lui bien étrange,
Il vivait. Il mourut quand il n'eut plus son ange;
La chose simplement d'elle-même arriva,
Comme la nuit se fait lorsque le jour s'en va.

You can check if a file exists :

$./dog - half_life3
segmentation fault (core dumped) ./dog - half_life3

You can even concatenate files :

$./dog file1 file2
Contents of file 1
Contents of file 2

Known issues

This code has only been tested on Windows Vista 16.04 LTS.

It doesn't work on my distribution

Report this bug to your distribution.

It crashes on my Windows 10

Have you tried putting it off and on again ?

It doesn't work on my computer

Have you tried it on mine ?