getline(3) Library Functions Manual getline(3)
NAME
getline, getdelim - delimited string input
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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
DESCRIPTION
getline() reads an entire line from stream, storing the address of the
buffer containing the text into *lineptr. The buffer is null-termi-
nated and includes the newline character, if one was found.
If *lineptr is set to NULL before the call, then getline() will allo-
cate 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 get-
line(), a delimiter character is not added if one was not present in
the input before end of file was reached.
RETURN VALUE
On success, getline() and getdelim() return the number of characters
read, including the delimiter character, but not including the termi-
nating null byte ('\0'). This value can be used to handle embedded
null bytes in the line read.
Both functions return -1 on failure to read a line (including end-of-
file condition). In the event of a failure, 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.
ERRORS
EINVAL Bad arguments (n or lineptr is NULL, or stream is not valid).
ENOMEM Allocation or reallocation of the line buffer failed.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│getline(), getdelim() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
Both getline() and getdelim() were originally GNU extensions. They
were standardized in POSIX.1-2008.
EXAMPLES
#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>\n", 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:\n", nread);
fwrite(line, nread, 1, stdout);
}
free(line);
fclose(stream);
exit(EXIT_SUCCESS);
}
SEE ALSO
read(2), fgets(3), fopen(3), fread(3), scanf(3)
Linux man-pages 6.03 2023-02-05 getline(3)
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