4.12 fgets, fgets_unlocked—get character string from a file or stream

Synopsis

#include <stdio.h>
char *fgets(char *restrict buf, int n, FILE *restrict fp);

#define _GNU_SOURCE
#include <stdio.h>
char *fgets_unlocked(char *restrict buf, int n, FILE *restrict fp);

#include <stdio.h>
char *_fgets_r(struct _reent *ptr, char *restrict buf, int n, FILE *restrict fp);

#include <stdio.h>
char *_fgets_unlocked_r(struct _reent *ptr, char *restrict buf, int n, FILE *restrict fp);

Description
Reads at most n-1 characters from fp until a newline is found. The characters including to the newline are stored in buf. The buffer is terminated with a 0.

fgets_unlocked is a non-thread-safe version of fgets. fgets_unlocked may only safely be used within a scope protected by flockfile() (or ftrylockfile()) and funlockfile(). This function may safely be used in a multi-threaded program if and only if they are called while the invoking thread owns the (FILE *) object, as is the case after a successful call to the flockfile() or ftrylockfile() functions. If threads are disabled, then fgets_unlocked is equivalent to fgets.

The functions _fgets_r and _fgets_unlocked_r are simply reentrant versions that are passed the additional reentrant structure pointer argument: ptr.

Returns
fgets returns the buffer passed to it, with the data filled in. If end of file occurs with some data already accumulated, the data is returned with no other indication. If no data are read, NULL is returned instead.

Portability
fgets should replace all uses of gets. Note however that fgets returns all of the data, while gets removes the trailing newline (with no indication that it has done so.)

fgets_unlocked is a GNU extension.

Supporting OS subroutines required: close, fstat, isatty, lseek, read, sbrk, write.