The term “Quine” refers to a special kind of Program (or shall I call Meta program?) that outputs its own complete source code as its only output. It is termed after the name of a philosopher Willard Van Orman Quine who did great study of indirect self references. There are certain distinct characteristics of what can be considered as Quine and what not.

A Quine can typically be written in any programming language that can compute and print a string – that means any programming language. Although in few it will be more convenient than others.

As per the definition the sole output of a Quine is its own source code there are few restrictions in defining the program as Quine.

  1. You are not supposed to perform a general File I/O to read and dump the source code. It can be safely assumed that the source code file is not available.
  2. Quine is not supposed to take any input. That way anybody can re-type the entire source code.
  3. There should be some code. Once a programmer played around the above to rules and wrote the shortest Quine – An empty program having nothing and giving the same output that is nothing. Clever Trick. That brought this third rule in place.

So how exactly do we define a Quine? A Quine will generally have two parts –

  1. Code to print the output.
  2. Data part that represents the program code as data.

A simple Quine in C language will be something like the code below:


main() { char *s="main() { char *s=%c%s%c; printf s,34,s,34); }"; printf(s,34,s,34); }


A Quine seem to serve no real purpose than to serve as a good programming puzzle to try out. Languages supporting proper reverse engineering and reflection certainly will provide a better way to write Quine.

I will not dive into historical evolution of Quine; but Wikipedia and Google will give a lot more material to those interested.

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