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3秒自动关闭窗口From Wikipedia, the free encyclopedia
This article needs additional citations for . Please help
by . Unsourced material may be challenged and removed. (April 2015) ()
In , a comma-separated values (CSV)
data (numbers and text) in . Each line of the file is a data . Each record consists of one or more , separated by . The use of the comma as a field separator is the source of the name for this .
The CSV file format is not standardized. The basic idea of separating fields with a comma is clear, but that idea gets complicated when the field data may also contain commas or even embedded line-breaks. CSV implementations may not handle such field data, or they may use quotation marks to surround the field. Quotation does not solve everything: some fields may need embedded quotation marks, so a CSV implementation may include escape characters or escape sequences.
In addition, the term "CSV" also denotes some closely related
that use different field delimiters. These include
and space-separated values. A delimiter that is not present in the field data (such as tab) keeps the format parsing simple. These alternate delimiter-separated files are often even given a .csv
despite the use of a non-comma field separator. This loose terminology can cause problems in . Many applications that accept CSV files have options to select the delimiter character and the quotation character.
CSV is a common
format that is widely supported by consumer, business, and scientific applications. Among its most common uses is moving tabular data between programs that natively operate on incompatible (often
or undocumented) formats. This works despite lack of adherence to
(or any other standard), because so many programs support variations on the CSV format for data import.
For example, a user may need to transfer information from a database program that stores data in a proprietary format, to a spreadsheet that uses a completely different format. The database program most likely can export its data as "CSV"; the exported CSV file can then be imported by the spreadsheet program.
proposes a specification for the CSV format, and this is the definition commonly used. However, in popular usage "CSV" is not a single, well-defined format. As a result, in practice the term "CSV" might refer to any file that:
using a character set such as , various
character sets (e.g. ), , or ,
consists of
(typically one record per line),
with the records divided into
separated by
(typically a single reserved character such as comma, semicolon, sometimes the delimiter may include optional spaces),
where every record has the same sequence of fields.
Within these general constraints, many variations are in use. Therefore, without additional information (such as whether
is honored), a file claimed simply to be in "CSV" format is not fully specified. As a result, many applications supporting CSV files allow users to preview the first few lines of the file and then specify the delimiter character(s), quoting rules, etc. If a particular CSV file's variations fall outside what a particular receiving program supports, it is often feasible to examine and edit the file by hand (i.e., with a ) or write a
or program to produce a conforming format.
Comma-separated values is a data format that pre-dates personal computers by more than a decade: the
(level H extended) compiler under
supported them in 1972. List-directed ("free form") input/output was defined in , approved in 1978. List-directed input used commas or spaces for delimiters, so unquoted character strings could not contain commas or spaces.
Comma-separated value lists are easier to type (for example into ) than fixed-column-aligned data, and were less prone to producing incorrect results if a value was punched one column off from its intended location.
Comma separated files are used for the interchange of database information between machines of two different architectures. The plain-text character of CSV files largely avoids incompatibilities such as
and . The files are largely human-readable, so it is easier to deal with them in the absence of perfect documentation or communication.
The main standardization initiative – transforming " fuzzy definition" into a more precise and
one – was in 2005, with RFC4180, defining CSV as a . Later, in 2013, some of RFC4180's deficiencies were tackled by a W3C recommendation.
published RFC7111 describing application of URI fragments to CSV documents. RFC7111 specifies how row, column, and cell ranges can be selected from a CSV document using position indexes.
In 2015 , in an attempt to enhance CSV with , publicized the first drafts of recommendations for CSV-metadata standards, that began as recommendations in December of the same year.
CSV formats are best used to represent sets or sequences of
in which each record has an identical list of fields. This corresponds to a single
in a , or to data (though not calculations) in a typical spreadsheet.
The format dates back to the early days of business computing and is widely used to pass data between computers with different internal word sizes, data formatting needs, and so forth. For this reason, CSV files are common on all computer platforms.
text file that uses a
to separate values (many implementations of CSV import/export tools allow other separators to be used). Simple CSV implementations may prohibit field values that contain a comma or other special characters such as . More sophisticated CSV implementations permit them, often by requiring " () characters around values that contain reserved characters (such as commas, double quotes, or less commonly, ). Embedded double quote characters may then be represented by a pair of consecutive double quotes, or by prefixing an
(for example in
CSV formats are not limited to a particular . They work just as well with
character sets (such as
or ) as with
(although particular programs that support CSV may have their own limitations). CSV files normally will even survive naive translation from one character set to another (unlike nearly all proprietary data formats). CSV does not, however, provide any way to indicate what character set is in use, so that must be communicated separately, or determined at the receiving end (if possible).
Databases that include multiple
cannot be exported as a single CSV file[].
Similarly, CSV cannot naturally represent
database or other data. This is because every CSV record is expected to have the same structure. CSV is therefore rarely appropriate for
such as those created with , , or other markup or word-processing technologies.
Statistical databases in various fields often have a generally relation-like structure, but with some repeatable groups of fields. For example, health databases such as the
typically repeat some questions for each child of a given parent (perhaps up to a fixed maximum number of children).
systems often include utilities that can "rotate" for example, a "parent" record that includes information about five children can be split into five separate records, each containing (a) the information on one child, and (b) a copy of all the non-child-specific information. CSV can represent either the "vertical" or "horizontal" form of such data.
In a relational database, similar issues are readily handled by creating a separate relation for each such group, and connecting "child" records to the related "parent" records using a
(such as an ID number or name for the parent). In markup languages such as XML, such groups are typically enclosed within a parent element and repeated as necessary (for example, multiple &child& nodes within a single &parent& node). With CSV there is no widely accepted single-file solution.
The name "CSV" indicates the use of the comma to separate data fields. Nevertheless, the term "CSV" is widely used to refer a large family of formats, which differ in many ways. Some implementations allow or require single or double quotation marks aroun and some reserve the very first record as a header containing a list of field names. The character set being used is undefined: some applications require a Unicode
(BOM) to enforce
interpretation (sometimes even a
BOM). Files that use the tab character instead of comma can be more precisely referred to as "TSV" for .
Other implementation differences include handling of more commonplace field separators (such as space or semicolon) and newline characters inside text fields. One more subtlety is the interpretation of a blank line: it can equally be the result of writing a record of zero fields, or a record of one
thus decoding it is ambiguous.
Reliance on the standard documented by
can simplify CSV exchange. However, this standard only specifies handling of text-based fields. Interpretation of the text of each field is still application-specific.
formalized CSV. It defines the
"text/csv", and CSV files that follow its rules should be very widely portable. Among its requirements:
MS-DOS-style lines that end with (CR/LF) characters (optional for the last line).
An optional header record (there is no sure way to detect whether it is present, so care is required when importing).
Each record "should" contain the same number of comma-separated fields.
Any field may be quoted (with double quotes).
Fields containing a line-break, double-quote or commas should be quoted. (If they are not, the file will likely be impossible to process correctly).
A (double) quote character in a field must be represented by two (double) quote characters.
The format can be processed by most programs that claim to read CSV files. The exceptions are: (a) programs may not support line-breaks within quoted fields, (b) programs may confuse the optional header with data or interpret the first data line as an optional header and (c) double quotes in a field may not be parsed correctly automatically.
In 2013 the
"CSV on the Web" working group began to specify technologies providing a higher interoperability for web applications using CSV or similar formats. The working group completed its work in February 2016, and is officially closed in March 2016 with the release of a set documents and W3C recommendations for modeling "Tabular Data", and enhancing CSV with
Many informal documents exist that describe "CSV" formats.
(summarized above) defines the format for the "text/csv"
registered with the .
Rules typical of these and other "CSV" specifications and implementations are as follows:
data format that has
separated by the
terminated by .
A CSV file does not require a specific , , or line terminator format (some software does not support all line-end variations).
A record ends at a line terminator. However, line-terminators can be embedded as data within fields, so software must recognize quoted line-separators (see below) in order to correctly assemble an entire record from perhaps multiple lines.
All records should have the same number of fields, in the same order.
Data within fields is interpreted as a sequence of , not as a sequence of bits or bytes (see , section 4.1). For example, the numeric quantity 65535 may be represented as the 5 ASCII characters "65535" (or perhaps other forms such as "0xFFFF", "0E+00", etc.); but not as a sequence of 2 bytes intended to be treated as a single binary integer rather than as two characters (e.g. the numbers
have a comma as their high order byte: ord(',')*256..ord(',')*257-1). If this "plain text" convention is not followed, then the CSV file no longer contains sufficient information to interpret it correctly, the CSV file will not likely survive transmission across differing computer architectures, and will not conform to the text/csv MIME type.
Adjacent fields must be separated by a single comma. However, "CSV" formats vary greatly in this choice of separator character. In particular, in
where the comma is used as a , semicolon, TAB, or other characters are used instead.
1997,Ford,E350
Any field may be quoted (that is, enclosed within double-quote characters). Some fields must be quoted, as specified in following rules.
"1997","Ford","E350"
Fields with embedded commas or double-quote characters must be quoted.
1997,Ford,E350,"Super, luxurious truck"
Each of the embedded double-quote characters must be represented by a pair of double-quote characters.
1997,Ford,E350,"Super, ""luxurious"" truck"
Fields with embedded line breaks must be quoted (however, many CSV implementations do not support embedded line breaks).
1997,Ford,E350,"Go get one now
they are going fast"
In some CSV implementations, leading and trailing spaces and tabs are trimmed (ignored). Such trimming is forbidden by , which states "Spaces are considered part of a field and should not be ignored."
1997, Ford, E350
not same as
1997,Ford,E350
According to , spaces outside quotes in a f however, the RFC also says that "Spaces are considered part of a field and should not be ignored." and "Implementors should 'be conservative in what you do, be liberal in what you accept from others' ( [8]) when processing CSV files."
1997, "Ford" ,E350
In CSV implementations that do trim leading or trailing spaces, fields with such spaces as meaningful data must be quoted.
1997,Ford,E350," Super luxurious truck "
Double quote processing need only apply if the field starts with a double quote. Note, however, that double quotes are not allowed in unquoted fields according to .
Los Angeles,34°03′N,118°15′W
New York City,40°42′46″N,74°00′21″W
Paris,48°51′24″N,2°21′03″E
The first record may be a "header", which contains column names in each of the fields (there is no reliable way to tell whether a f however, it is uncommon to use characters other than letters, digits, and underscores in such column names).
Year,Make,Model
1997,Ford,E350
2000,Mercury,Cougar
Description
ac, abs, moon
Venture "Extended Edition"
Venture "Extended Edition, Very Large"
Grand Cherokee
MUST SELL!
air, moon roof, loaded
The above table of data may be represented in CSV format as follows:
Year,Make,Model,Description,Price
1997,Ford,E350,"ac, abs, moon",3000.00
1999,Chevy,"Venture ""Extended Edition""","",4900.00
1999,Chevy,"Venture ""Extended Edition, Very Large""",,5000.00
1996,Jeep,Grand Cherokee,"MUST SELL!
air, moon roof, loaded",4799.00
Example of a USA/UK CSV file (where the
is a period/full stop and the value separator is a comma):
Year,Make,Model,Length
1997,Ford,E350,2.34
2000,Mercury,Cougar,2.38
Example of an analogous European CSV/ file (where the
is a comma and the value separator is a semicolon):
1997;FE350;2,34
2000;MC2,38
The latter format is not
compliant. Compliance could be achieved by the use of a comma instead of a semicolon as a separator and either the
for the representation of the
or the practice of quoting all numbers that have a decimal mark.
It has been suggested that
into this article. () Proposed since April 2015.
The CSV file format is supported by almost all
and . Many
have libraries available that support CSV files. Many implementations support changing the field-separator character and some quoting conventions, although it is safest to use the simplest conventions, to maximize the recipients' chances of handling the data.
will open .csv files, but depending on the system's regional settings, it may expect a
as a separator instead of a comma, since in some languages the comma is used as the . Excel supports the use of a "sep= " row at the beginning of the file to change the expected delimiter (example: sep=; will cause Excel to use ";" as the delimiter). Excel also applies some magic, such as reformatting what looks like numbers or dates, eliminating leading + or 0, which breaks phone numbers, or a leading = makes the cell a formula, where function names must be in the opener's local language. Also, many regional versions of Excel will not be able to deal with Unicode in CSV. One simple solution when encountering such difficulties is to change the filename extension from .csv to .txt; then opening the file from an already running Excel instance with the "Open" command, where the user can manually specify the delimiters, encoding, format of columns, etc.
handle CSV files and pasted text with a Text Import dialog asking the user to manually specify the delimiters, encoding, format of columns, etc.
, the Apple equivalent of , supports import and export of CSV files as well. In fact, this feature is one that can be expected on almost any spreadsheet editing program.
There are many utility programs on -style systems that can deal with at least some CSV files. Many such utilities have a way to change the delimiter character, but lack support for any other variations (or for Unicode). Some of the useful programs are:
(-s to change the delimiter character(s))
(-d to change the delimiter character)
(-d to change the delimiter character(s))
(-t to change the delimiter character)
(-t to change the delimiter character)
(-f to skip comparing the first N fields)
(using csv-nav mode)
(-F to change the delimiter character)
Shafranovich, Y. (October 2005). . . p. 1. RFC 4180. .
states, "This RFC documents the format of comma separated values (CSV) files and formally registers the "text/csv" MIME type for CSV in accordance with ".
. Edoceo, Inc 2014.
(PDF) (first ed.), July 1972, p. 17, GC28-6, For users familiar with the predecessor FORTRAN IV G and H processors, these are the major new language capabilities
"List-Directed I/O", , Oracle
See , the first W3C recommendation scoped in CSV and filling some of RFC4180's deficiencies.
*Creativyst (2010), ,
CSV WG. 2013.
(on GitHub)
(W3C Recommendation)
states, "Within the header and each record, there may be one or more fields, separated by commas."
from the original on . (Has file descriptions of delimited ASCII (.DEL) (including comma- and semicolon-separated) and non-delimited ASCII (.ASC) files for data transfer.)
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