FPARSELN(3) | Library Functions Manual | FPARSELN(3)

# NAME

`fparseln` — return the next logical line from a stream

# SYNOPSIS

System Utilities Library (libutil, -lutil)
`#include <stdio.h>`
`#include <util.h>`

char *
`fparseln`(FILE *stream, size_t *len, size_t *lineno, const char delim[3], int flags);

# DESCRIPTION

The `fparseln`() function returns a pointer to the next logical line from the stream referenced by stream. This string is null terminated, contains no trailing newline, and is dynamically allocated on each invocation. It is the responsibility of the caller to free the pointer.

By default, if a character is escaped, both it and the preceding escape character will be present in the returned string. Various flags alter this behaviour.

The meaning of the arguments is as follows:

stream
  The stream to read from.
len
  If not `NULL`, the length of the string is stored in the memory location referenced by len.
lineno
  If not `NULL`, the value of the memory location to which lineno references is incremented by the number of lines actually read from the file.
delim
  Contains the escape, continuation, and comment characters. If a character is NUL then processing for that character is disabled. If `NULL`, all characters default to values specified below. The contents of delim is as follows:
  delim[0]
    The escape character, which defaults to ‘`\`’, is used to remove any special meaning from the next character.
  delim[1]
    The continuation character, which defaults to ‘`\`’, is used to indicate that the next line should be concatenated with the current one if this character is the last character on the current line and is not escaped.
  delim[2]
    The comment character, which defaults to ‘`#`’, if not escaped indicates the beginning of a comment that extends until the end of the current line.
flags
  If non-zero, alter the operation of `fparseln`(). The various flags, which may be OR'ed together, are:
  `FPARSELN_UNESCCOMM`
    Remove escape preceding an escaped comment.
  `FPARSELN_UNESCCONT`
    Remove escape preceding an escaped continuation.
  `FPARSELN_UNESCESC`
    Remove escape preceding an escaped escape.
  `FPARSELN_UNESCREST`
    Remove escape preceding any other character.
  `FPARSELN_UNESCALL`
    All of the above.

# RETURN VALUES

Upon successful completion a pointer to the parsed line is returned; otherwise, `NULL` is returned.

Internally, the `fparseln`() function uses fgetln(3), so all error conditions that apply to fgetln(3) apply to `fparseln`() as well. In addition `fparseln`() may set errno to `ENOMEM` and return `NULL` if it runs out of memory.

# SEE ALSO

fgetln(3)

June 13, 2025 | Debian