GETLINE(3) Linux Programmer's Manual GETLINE(3)

getline, getdelim - delimited string input

#include <stdio.h>
ssize_t getline(char **lineptr, size_t *n, FILE *stream);
ssize_t getdelim(char **lineptr, size_t *n, int delim, FILE *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:

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 and *n is set 0 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.
Both functions return -1 on failure to read a line (including end-of-file condition). In the event of an error, errno is set to indicate the cause.

Bad arguments (n or lineptr is NULL, or stream is not valid).
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

Both getline() and getdelim() were originally GNU extensions. They were standardized in 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 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 %zu:\n", nread); fwrite(line, nread, 1, stdout); }
free(line); fclose(stream); exit(EXIT_SUCCESS); }

read(2), fgets(3), fopen(3), fread(3), scanf(3)
2019-03-06 GNU