The History Behind the Definition of a 'String'

I have never thought about until recently, but I'm not sure why we call strings strings. I am a .NET programmer, but I believe the concept of strings exist in virtually every programming language.

Outside of programming, I don't believe I've heard the word string used to describe words or letters. A quick Google of, 'Define: string' yields a bunch of definitions that have nothing to do with the concept of letters, words, or anything of the nature associated to programming.

My guess of it, is that, back in the day, strings were really just arrays of characters of a particular length, often with a delimiting character at the end. But, I don't see a natural transition from 'character array' to string.

Can someone offer up some insight to why we call strings strings?

My assumption has always been that the programming term originated from the following definition of the word "string" (from Merriam-Webster):

> (1): a series of things arranged in or as if in a line <a string of cars> <a string of names> > > (2): a sequence of like items (as bits, characters, or words)

Since a string in programming is simply an ordered sequence of characters, referring to this as a "string of characters" (or simply "string") seems like the most probable origin.

From this reference:

> The 1971 OED (p. 3097) quotes an 1891 > Century Dictionary on a source in the > Milwaukee Sentinel of 11 Jan. 1898 > (section 3, p. 1) to the effect that > this is a compositor's term. Printers > would paste up the text that they had > generated in a long strip of > characters. (Presumably, they were > paid by the foot, not by the word!) > The quote says that it was not unusual > for compositors to create more than > 1500 (characters?) per hour.

From searching through the ACM bibliography it seems the word string acquired its meaning in computer science during the 1960s. At the beginning a string is a general kind of sequence or list, e.g. http://doi.acm.org/10.1145/610937.610965">A command language for handling strings of symbols from 1958.

http://doi.acm.org/10.1145/364099.364236">This article explicitly mentions "character strings" in 1964.

Unfortunately I can't access the full texts, which are behind a toll booth.

I had guessed that "string" was in use by mathematicians long before its adoption in programming languages. Turing machines effectively operate on strings. Turing may not have used the term, but it is used everywhere in automata textbooks, going back decades.

The earliest reference I could find was a fragment in Google books of a 1944 article "Recursively enumerable sets of positive integers and their decision problems" by logician Emil Post in Bulletin of the AMS. Fortunately, AMS provides online archives of complete articles free for download. Here is a link: http://www.ams.org/journals/bull/1944-50-05/S0002-9904-1944-08111-1/S0002-9904-1944-08111-1.pdf

I think there is little doubt that he is using "string" in the conventional sense used in computer science. P. 286 "For working purposes, we in- troduce the letter b, and consider "strings" of 1's and b's such as 11b1bb1. An operation on such strings such as "b1bP produces P1bb1" we term a normal operation. This particular normal operation is ap- plicable only to strings starting with b1b, and the derived string is then obtained from the given string by first removing the initial b1b, and then tacking on 1bb1 at the end. Thus b1bb becomes b1bb1."

I suspect it's because string originally meant just a sequence of data values: "I'll just string these together" etc. These values didn't have to be characters. One very common use for this general concept happened to be a sequence of characters, and this took over as the general meaning of the word.

The earliest reference I could find in computing is from March 1963's METEOR: A LISP Interpreter for String Transformations by Daniel G. Bobrow at MIT's AI Labs.

However, definition 15d. in the Oxford English Dictionary is:

> Computing A linear sequence of records or data.

... and with a first quotation from a 1956 Journal of the Association for Computing Machinery:

> Areas are set aside for shuttling strings of control fields back and forth until a completely sorted sequence is obtained.

This use naturally follows on from definition 15c.:

> Math., etc. A sequence of symbols or linguistic elements in a definite order.

... and first used in Clarence Irving Lewis and Cooper Harold Langford's Symbolic Logic (1932):

> Propositions are not strings of marks, or series of sounds, except incidentally.

This in turn follows on from many other, much earlier definitions for things in a line.

The word was originally used to differentiate between a set of values to which the particular order of elements doesn't matter (for instance, a set of random samples of measurements) and another that could only have its meaning preserved when the order is also preserved. Originally a string could be a set of any kind of values, but since in the post-mainframe era a string of characters is by far the most common kind, the fact that the values are characters became a "default".

In a talk about Javascript history Douglas Crockford says "Nobody knows" and gives a few alternatives: http://www.youtube.com/watch?v=RO1Wnu-xKoY#t=2989

I found the report which in it, allegedly, there is the first reference ever in computer history to a series of characters as a "string". I think it's at the top right column of page 4 of the pdf, which is numbered 47:

http://web.eecs.umich.edu/~bchandra/courses/papers/Naure_Algol60.pdf

A string is a sequence of discrete objects (usually char).

Given that, I would probably venture a guess that it may have to do with a metaphor related to "string of pearls". Each bead on the string is a single character.

It's called a strings, because it's actually an array of char type elements.

That being said, they are "stringing together" (or is it strung together) via this array, which turns them into a "string".