#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():
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.
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.
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
FILE *fp;
char *line = NULL;
size_t len = 0;
ssize_t read;
fp = fopen("/etc/motd", "r");
if (fp == NULL)
exit(EXIT_FAILURE);
while ((read = getline(&line, &len, fp)) != -1) {
printf("Retrieved line of length %zu :\n", read);
printf("%s", line);
}
free(line);
fclose(fp);
exit(EXIT_SUCCESS);
}