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In computing, the end of line (EOL) is the boundary that marks where one line of text stops and the next begins. It is not one fixed character. Some systems mark it with a carriage return followed by a line feed (CR-LF), and others use a line feed (LF) alone. The correct choice depends on the file format, network protocol, programming language, or device you are working with, so the label “EOL” on its own never tells you which characters are in use.
The three sequences you will meet
Three forms come up repeatedly. Each is built from one or two control characters, and the two control characters do different jobs on a printer or terminal.
| Name | Characters | Decimal / hex (ASCII) | Effect on the cursor or print position | Where the sources place it |
|---|---|---|---|---|
| CR (carriage return) | CR | 13 / 0x0D | Moves the cursor to the beginning of the current line without advancing to the next line. | National Instruments (NI) LabVIEW documentation gives this description as a vendor explanation. |
| LF (line feed) | LF | 10 / 0x0A | Moves down to the next line without returning to the beginning of the current line. | NI LabVIEW documentation; RFC 1849 says ISO C and many modern operating systems mark end of line with a single character, typically ASCII LF. |
| CR-LF | CR followed by LF | 13 then 10 / 0x0D 0x0A | Returns to the beginning of the line and then moves down to the next line. | RFC 318 (April 1972, by John Postel) specifies it for Telnet; RFC 1849 describes it for Internet transmission such as SMTP; NI names it the End of Line character constant in LabVIEW. |
The values in the table are character-code values, not survey figures. They are the same in every table row only because each one is taken from the ASCII code assignments the sources cite.
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What “end of line” actually means
End of line describes a position in a stream of text, not a specific keystroke or byte. A text editor may show a line break as a single visual event, but the file underneath stores whatever sequence its format expects. RFC 1849 states the point directly: “How the end of a text line is represented depends on the context and the implementation.” That is why the same visual break can be one byte in one file and two bytes in another.
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Two terms are often confused. “Newline” and “end of line” are used loosely as synonyms in everyday speech. In specifications, though, a line ending is the exact sequence written to mark the boundary, and it must match whatever the reader expects.
Where each convention is used
Internet protocols and Telnet
RFC 318, titled “The End of the Line Convention,” defines the end of a line of text as the sequence Carriage Return followed by Line Feed. It was written for Telnet, the remote terminal protocol, and it does not describe every file or operating system. RFC 1849 uses the same CR-LF pair for Internet transmission such as SMTP, which is why mail and many other text-based protocols expect that sequence on the wire, even when the local system stores files differently.
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C, Unix-style systems, and many modern operating systems
RFC 1849 notes that ISO C and many modern operating systems indicate end of line with a single character, typically ASCII LF. Code that reads or writes plain text in these environments usually sees LF alone. This is a convention of the language and platform, not a rule that applies to network traffic.
Printing and device behavior
The meaning of LF was defined in printing terms before it became a file convention. A U.S. federal ASCII standard amendment says that, where appropriate, the character “may have the meaning ‘New Line’ (NL), a format effector which controls the movement of the printing point to the first printing position on the next printing line.” That description explains why LF alone moves the paper down without returning the print head. Printers and some terminals therefore need CR to start at the left margin, which is the reason CR-LF became common in device output.
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Development environments
NI’s LabVIEW documentation describes CR, LF, and the CR-LF pair as separate constants, and it presents the CR-LF pair as its End of Line character constant. The documentation is specific to LabVIEW. It shows how that environment exposes the characters, not how every platform behaves.
How to choose the right line ending
When you write or convert text, work through these steps in order:
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- Identify the format or protocol the output must satisfy. A file format specification, a protocol RFC, or a device manual is the authority for that output.
- If a specification names a sequence, use exactly that sequence, for example CR-LF for Telnet or Internet mail transmission as described in RFC 318 and RFC 1849.
- If no specification applies, follow the documented behavior of the language, runtime, or operating system that will read the file, such as the single-character LF described in RFC 1849 for ISO C and many modern systems.
- Check the result. Open the file or capture the stream with a tool that displays raw bytes, and confirm the boundary characters match what the reader expects.
Common reading and parsing mistakes
- Assuming one convention everywhere. A parser written only for LF may leave a stray CR at the end of every line when it receives CR-LF input, and the trailing character may cause comparisons to fail.
- Trusting the label. A file called “EOL” or “newline” tells you nothing about the bytes inside. Check the format documentation or the raw bytes.
- Mixing conventions in one file. Output that combines CR-LF and LF can look correct in one viewer and wrong in another.
- Treating a vendor’s description as universal. NI’s explanation of CR and LF behavior is written for LabVIEW. Protocol and language behavior should be confirmed from the relevant specification or runtime documentation.
Limits of what the sources establish
The definition itself is stable across the sources: the end of a line is a boundary, and its representation is set by context. The specific behavior of each control character is described by NI, a vendor, and the RFCs describe the conventions they were written for. The sources do not provide a survey of which operating system or application uses which sequence, so any claim about the prevalence of a convention in a particular product should be checked against that product’s own documentation.
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The ASCII values and the RFC dates given above are accurate to the sources cited. Specific implementations, such as particular editors, compilers, or device firmware, may differ and should be verified individually.
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