man3/getline.3

.\" Copyright (c) 2001 John Levon <moz@compsoc.man.ac.uk>
.\" Based in part on GNU libc documentation
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH GETLINE 3  2021-03-22 "GNU" "Linux Programmer's Manual"
.SH NAME
getline, getdelim \- delimited string input
.SH SYNOPSIS
.nf
.B #include <stdio.h>
.PP
.BI "ssize_t getline(char **restrict " lineptr ", size_t *restrict " n ,
.BI "                FILE *restrict " stream );
.BI "ssize_t getdelim(char **restrict " lineptr ", size_t *restrict " n ,
.BI "                int " delim ", FILE *restrict " stream );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getline (),
.BR getdelim ():
.nf
    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.SH DESCRIPTION
.BR getline ()
reads an entire line from \fIstream\fP,
storing the address of the buffer containing the text into
.IR "*lineptr" .
The buffer is null-terminated and includes the newline character, if
one was found.
.PP
If
.I "*lineptr"
is set to NULL and
.I *n
is set 0 before the call, then
.BR getline ()
will allocate a buffer for storing the line.
This buffer should be freed by the user program
even if
.BR getline ()
failed.
.PP
Alternatively, before calling
.BR getline (),
.I "*lineptr"
can contain a pointer to a
.BR malloc (3)\-allocated
buffer
.I "*n"
bytes in size.
If the buffer is not large enough to hold the line,
.BR getline ()
resizes it with
.BR realloc (3),
updating
.I "*lineptr"
and
.I "*n"
as necessary.
.PP
In either case, on a successful call,
.I "*lineptr"
and
.I "*n"
will be updated to reflect the buffer address and allocated size respectively.
.PP
.BR getdelim ()
works like
.BR getline (),
except that a line delimiter other than newline can be specified as the
.I delimiter
argument.
As with
.BR getline (),
a delimiter character is not added if one was not present
in the input before end of file was reached.
.SH RETURN VALUE
On success,
.BR getline ()
and
.BR getdelim ()
return the number of characters read, including the delimiter character,
but not including the terminating null byte (\(aq\e0\(aq).
This value can be used
to handle embedded null bytes in the line read.
.PP
Both functions return \-1 on failure to read a line (including end-of-file
condition).
In the event of a failure,
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
Bad arguments
.RI ( n
or
.I lineptr
is NULL, or
.I stream
is not valid).
.TP
.B ENOMEM
Allocation or reallocation of the line buffer failed.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR getline (),
.BR getdelim ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
Both
.BR getline ()
and
.BR getdelim ()
were originally GNU extensions.
They were standardized in POSIX.1-2008.
.SH EXAMPLES
.EX
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>

int
main(int argc, char *argv[])
{
    FILE *stream;
    char *line = NULL;
    size_t len = 0;
    ssize_t nread;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <file>\en", argv[0]);
        exit(EXIT_FAILURE);
    }

    stream = fopen(argv[1], "r");
    if (stream == NULL) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    while ((nread = getline(&line, &len, stream)) != \-1) {
        printf("Retrieved line of length %zd:\en", nread);
        fwrite(line, nread, 1, stdout);
    }

    free(line);
    fclose(stream);
    exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR read (2),
.BR fgets (3),
.BR fopen (3),
.BR fread (3),
.BR scanf (3)