When to use the terms "delimiter," "terminator," and "separator"

Asked 2/2, 2012 at 19:36 Answered 31/8, 2022 at 16:25

Solved delimiter terminology semantics separator

What are the semantics behind usage of the words "delimiter," "terminator," and "separator"? For example, I believe that a terminator would occur after each token and a separator between each token. Is a delimiter the same as either of these, or are they simply forms of a delimiter?

SO has all three as tags, yet they are not synonyms of each other. Is this because they are all truly different?

Backpedal answered 2/2, 2012 at 19:36 Comment(0)

Technically a delimiter goes between things, perhaps in order to tell you where one field ends and another begins, such as in a comma-separated-value (CSV) file.

A terminator goes at the end of something, terminating the line/input/whatever.

A separator can be a delimiter or anything else that separates things. Consider the spaces between words in the English language for example.

You could argue that a newline character is a line terminator, a delimiter of lines or something that separates two lines. For this reason there are a few different newline-type characters in the Unicode specification.

Fond answered 2/2, 2012 at 19:44 Comment(2)

So, what's the difference between a delimiter and a separator? Your explanation seems to imply that both commas in CSV and spaces in English are both delimiters and separators; is this correct? – Stichometry 3/9, 2012 at 21:3

Yes, they end up having pretty much the same meaning. Delimiting strings like in CSV files tells you where the limits of the data are. The terms are broadly equivalent, albeit with subtly different implications. Ian Dickinson's answer provides a more complete explanation of the difference. – Fond 5/9, 2012 at 10:26

A delimiter denotes the limits of something, where it starts and where it ends. For example:

"this is a string"

has two delimiters, both of which happen to be the double-quote character. The delimiters indicate what's part of the thing, and what is not.

A separator distinguishes two things in a sequence:

one, two
1\t2
code();  // comment

The role of a separator is to demarcate two distinct entities so that they can be distinguished. (Note that I say "two" because in computer science we're generally talking about processing a linear sequence of characters).

A terminator indicates the end of a sequence. In a CSV, you could think of the newline as terminating the record on one line, or as separating one record from the next.

Token boundaries are often denoted by a change in syntax classes:

foo()

would likely be tokenised as word(foo), lparen, rparen - there aren't any explicit delimiters between the tokens, but a tokenizer would recognise the change in grammar classes between alpha and punctuation characters.

The categories aren't completely distinct. For example:

[red, green, blue]

could (depending on your syntax) be a list of three items; the brackets delimit the list and the right-bracket terminates the list and marks the end of the blue token.

As for SO's use of those terms as tags, they're just that: tags to indicate the topic of a question. There isn't a single unified controlled vocabulary for tags; anyone with enough karma can add a new tag. Enough differences in terminology exist that you could never have a single controlled tag vocabulary across all of the topics that SO covers.

Salesgirl answered 2/2, 2012 at 21:14 Comment(2)

This definition of "delimiter" is not consistent with Wikipedia's. There, a "delimiter" pretty much covers what you call a "separator". – Andalusia 2/2, 2017 at 12:57

True, but his version makes more sense than the one in Wikipedia. A delimiter delimits things (like "..."), a separator separates things (like ..., ...). Whoever caused the mixed up common definition that makes people call separators "delimiter" did no service to anyone. – Calendre 29/7, 2020 at 22:28

Technically a delimiter goes between things, perhaps in order to tell you where one field ends and another begins, such as in a comma-separated-value (CSV) file.

A terminator goes at the end of something, terminating the line/input/whatever.

A separator can be a delimiter or anything else that separates things. Consider the spaces between words in the English language for example.

Fond answered 2/2, 2012 at 19:44 Comment(2)

A delimiter is one or two markers that show the start and end of something. They're needed because we don't know how long that 'something' will be. We can have either: 1. a single delimiter, or 2. a pair of pair-delimiters

[a, b, c, d, e] each comma (,) is a single delimiter. The left and right brackets, ([, ]) are pair-delimiters.
"hello", the two quote symbols (") are pair-delimiters

A seperator is a synonym of a "delimiter", but from my experience it usually refers to field delimiters. A field delimiter acts as a divider between one field and the one following it, which is why is can be though of as "separating" them.

<file1>␜<file2>␜<file3>, the file separator character (␜), despite explicitly the name having "separator", is both a delimiter and a separator

A terminator marks the end of a group of things, again needed because we don't know how long it is.

abdefa\0, here the null character \0 is a terminator that tells us the string has ended.
foo\n, here the newline character \n is a terminator that tells us the line has ended.

The terms, delimiter, separator originate from the classical idea of storage, conceptually, being comprised of files, records, and fields, (a file has many records, a record has many fields). In this context, a single delimiter and pair-delimiters might be called record delimiters and field delimiters. Because of the historical significance of files-records-field taxonomy, this terms have a more widespread usage (see Wikipedia page for Delimiter).

Below are two files, each with three records with each record having four fields:
```
martin,rodgers,33,28000\n
timothy,byrd,22,25000\n
marion,summers,35,37000\n
===
lucille,rowe,28,33000\n
whitney,turner,24,19000\n
fernando,simpson,35,40900\n
```
Here, , and \n as we know are single delimiters, but they might also be called a record delimiters and field delimiters respectively.

For complex nested structures, a terminator can also be a delimiter/separator (they're not mutually exclusive definitions). From the previous example, the === marker from inside a file could be considered a terminator (it's the end of the file). But when we look at many files, the === acts like a delimiter/separator.

Consider lines in a UNIX file
```
This is line 1\n
This is line 2\n
This is line 3\n
```
The newlines are both terminators (they tell us where the string ends) and are delimiters (they tell us where each line begins and ends). From Wikipedia:

Two ways to view newlines, both of which are self-consistent, are that newlines either separate lines or that they terminate lines.

Really you'll only need to say "terminator" when you're talking at one individual item, (just one string 1234\0, just one line abcd\n, etc.) -- and it'll be unclear whether the terminator in this context could also be a delimiter in a more complex parent structure.

Einsteinium answered 8/2, 2017 at 10:10 Comment(0)

This response is in context of CSV because all of the provided answers focus on English language instead.

Delimiters are all elements mentioned in the given CSV specification that describe the boundaries of stuff, separator is a common name for field delimiters, terminator is a common name for record delimiters.

Delimiter is a part of CSV format specification, it defines boundaries and doesn't have to be a printable character.

Terminators, separators and field qualifiers are delimiters but are not necessary to specify a CSV format, e.g. 10 columns field delimiter and 30 columns record delimiter mean each 30 columns are one record and each 10 columns are one field (usually padded with white space). In other words CSV format without separators has a constant field and record length, e.g.:

will      smith     1         chris     rock      0

Terminator is a delimiter that marks the end of a single CSV record and is usually represented either by Line Feed (LF), a Carriage Return (CR) or a combination of both (e.g. CRLF), e.g.:

will      smith     1         
chris     rock      0

Separator is a delimiter that marks the division between CSV fields and is most often represented by a comma (or a semicolon), it has been introduced to store dynamic length values, e.g. two comma separated records in CSV format with CRLF terminator after 1 and 0:

will,smith,1
chris,rock,0

Field qualifier is a delimiter usually used in pairs instead of escape sequence. It is a printable character that isn't allowed in the field value (unless given CSV format specification provides the escape sequence) and marks the beginning and the end of a field, it was introduced to store values containing separators, e.g. this CSV has 2 records with 3 fields each but 3rd field value can contain a semicolon that otherwise acts as a fields separator:

will;smith;"rich;famous;slaps people"
chris;rock;"rich;famous;gets slapped"

Escape sequence is a character (or a set of characters) that marks anything that follows the escape sequence as non-significant and therefore as a part of the field value (e.g. backslash might specify the immediately following separator as a part of the value). This sequence can escape one or multiple characters, e.g. CSV with \ as a 1 character escape sequence:

will;smith;rich\;famous\;slaps people 100\\100% of time
chris;rock;rich\;famous\;slaps people 0\\100% of time

Elflock answered 16/3, 2016 at 17:54 Comment(0)

Interesting question and answers. To summarize, 1) delimiter marks the "limits" of something, i.e. beginning and/or end; 2) terminator is just a special term for "end delimiter"; 3) separator entails there are items on both sides of it (unlike delimiter).

Best example I can think of for a start delimiter is the start-comment markers in programming languages ("#", "//", etc.).

Best example I can think of for a terminator (end delimiter) is the newline character in Unix. It's a misnomer -- it always terminates a (possibly empty) line but doesn't always start a new line, i.e. when it is the last character in a file. Maybe a better common example is the simple period for sentences.

Best example I can think of for a separator is the simple comma. Note that comma never appears in English without text both before and after it.

Interesting to note that none of these is necessarily limited to single-character. In fact awk (or maybe only gawk?) in Unix allows FS (field separator) to be any regexp.

Also, although "any non-zero amount of whitespace" is considered a "word delimiter" in e.g. the wc command, there are also zero-width "word boundary" specifiers in regexps (e.g. \b). Interesting to ponder whether such zero-width items/boundaries could be considered "delimiters" as well. I tend to think not (too much of a stretch).

Chalet answered 26/9, 2015 at 17:24 Comment(0)

Delimiter

There are a couple of senses for delimiter:

As the space used in sentences (frontier).
A delimiter is like a frontier, it exists between countries.
In that sense, there must be two countries to have a frontier.
An space usually exists between words, but not at the end. The space delimits words but does not terminate sentences (collection of words). The sentence:

This is a short sentence.

Has four spaces, they act as word delimiters. There is no ending space.
In fact, there are two additional delimiters usually not named: The start and end of the sentence. Like the ^ and $ used in regular expressions to mark the start and end of an string of text.
And, in human language, there are punctuation marks (dot, comma, semicolon, colon, etc.) that serve also as word delimiters (additionally to spaces)
As used in quotes (boundary).
A sentence like:

“This is a short sentence.”

Is delimited (start and end) by the double quotes (“”). In this sense it is like "balanced delimiters" (Balanced Brackets in Wikipedia).

Some may argue the frontier and boundary are essentially the same, and, under some conditions they actually are correct.

Separator

Is exactly the same as the first sense (above) of a delimiter (a frontier).

So, a separator is a synonym of delimiter in many computer uses.

Terminator

Demarcate the end of an individual "field".
Like the newlines in a Unix text file. Each line is terminated by a NewLine (\n).
In a proper Unix text file all lines are terminated (even the last one). Like paragraphs are terminated by a newline in human language.

Or, more strictly, as the NUL (\0) is the terminator of a C string:

A string is defined as a contiguous sequence of code units terminated by the first zero code unit (often called the NUL code unit).

So, a terminator character is also a delimiter but must also appear at the end.

Delimiter

Separator

Terminator

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