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[thirdparty/man-pages.git] / man3 / getline.3

.\" Copyright (c) 2001 John Levon <moz@compsoc.man.ac.uk>
.\" Based in part on GNU libc documentation
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH GETLINE 3  2021-03-22 "Linux man-pages (unreleased)"
.SH NAME
getline, getdelim \- delimited string input
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.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 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.
.PP
If
.I *lineptr
was set to NULL before the call, then the buffer should be freed by the
user program even on failure.
.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 STANDARDS
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)