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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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getline(3) Library Functions Manual getline(3)
getline, getdelim - delimited string input
Standard C library (libc, -lc)
#include <stdio.h>
ssize_t getline(char **restrict lineptr, size_t *restrict n,
FILE *restrict stream);
ssize_t getdelim(char **restrict lineptr, size_t *restrict n,
int delim, FILE *restrict stream);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getline(), getdelim():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_GNU_SOURCE
getline() reads an entire line from stream, storing the address of
the buffer containing the text into *lineptr. The buffer is null-
terminated and includes the newline character, if one was found.
If *lineptr is set to NULL before the call, then getline() will
allocate a buffer for storing the line. This buffer should be
freed by the user program even if getline() failed.
Alternatively, before calling getline(), *lineptr can contain a
pointer to a malloc(3)-allocated buffer *n bytes in size. If the
buffer is not large enough to hold the line, getline() resizes it
with realloc(3), updating *lineptr and *n as necessary.
In either case, on a successful call, *lineptr and *n will be
updated to reflect the buffer address and allocated size
respectively.
getdelim() works like getline(), except that a line delimiter
other than newline can be specified as the delimiter argument. As
with getline(), a delimiter character is not added if one was not
present in the input before end of file was reached.
On success, getline() and getdelim() return the number of
characters read, including the delimiter character, but not
including the terminating null byte ('\0'). This value can be
used to handle embedded null bytes in the line read.
At end of file, both functions return -1 with the file stream end-
of-file indicator set. On error, both functions return -1 with
the file stream error indicator set, and errno is set to indicate
the error.
If *lineptr was set to NULL before the call, then the buffer
should be freed by the user program even on failure.
EINVAL Bad arguments (n or lineptr is NULL, or stream is not
valid).
ENOMEM Allocation or reallocation of the line buffer failed.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ getline(), getdelim() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
GNU, POSIX.1-2008.
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
FILE *stream;
char *line = NULL;
size_t size = 0;
ssize_t nread;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
exit(EXIT_FAILURE);
}
stream = fopen(argv[1], "r");
if (stream == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
while ((nread = getline(&line, &size, stream)) != -1) {
printf("Retrieved line of length %zd:\n", nread);
fwrite(line, nread, 1, stdout);
}
free(line);
fclose(stream);
exit(EXIT_SUCCESS);
}
read(2), fgets(3), fopen(3), fread(3), scanf(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 getline(3)
Pages that refer to this page: fgetc(3), gets(3), rpmatch(3), scanf(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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