FGETS(3)                   POSIX Programmer's Manual                  FGETS(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       fgets -- get a string from a stream

SYNOPSIS
       #include <stdio.h>

       char *fgets(char *restrict _s, int _n, FILE *restrict stream);

DESCRIPTION
       The functionality described on this reference page is aligned with the
       ISO C standard. Any conflict between the requirements described here
       and the ISO C standard is unintentional. This volume of POSIX.1-2017
       defers to the ISO C standard.

       The fgets() function shall read bytes from stream into the array
       pointed to by _s until _n-1 bytes are read, or a <newline> is read and
       transferred to _s, or an end-of-file condition is encountered. A null
       byte shall be written immediately after the last byte read into the
       array.  If the end-of-file condition is encountered before any bytes
       are read, the contents of the array pointed to by _s shall not be
       changed.

       The fgets() function may mark the last data access timestamp of the
       file associated with stream for update. The last data access timestamp
       shall be marked for update by the first successful execution of
       fgetc(), fgets(), fread(), fscanf(), getc(), getchar(), getdelim(),
       getline(), gets(), or scanf() using stream that returns data not
       supplied by a prior call to ungetc().

RETURN VALUE
       Upon successful completion, fgets() shall return _s.  If the stream is
       at end-of-file, the end-of-file indicator for the stream shall be set
       and fgets() shall return a null pointer.  If a read error occurs, the
       error indicator for the stream shall be set, fgets() shall return a
       null pointer, and shall set errno to indicate the error.

ERRORS
       Refer to fgetc().

       The following sections are informative.

EXAMPLES
   Reading Input
       The following example uses fgets() to read lines of input. It assumes
       that the file it is reading is a text file and that lines in this text
       file are no longer than 16384 (or {LINE_MAX} if it is less than 16384
       on the implementation where it is running) bytes long. (Note that the
       standard utilities have no line length limit if sysconf(_SC_LINE_MAX)
       returns -1 without setting errno.  This example assumes that
       sysconf(_SC_LINE_MAX) will not fail.)


           #include <limits.h>
           #include <stdio.h>
           #include <unistd.h>
           #define MYLIMIT 16384

           char *line;
           int line_max;
           if (LINE_MAX >= MYLIMIT) {
               // Use maximum line size of MYLIMIT. If LINE_MAX is
               // bigger than our limit, sysconf() cannot report a
               // smaller limit.
               line_max = MYLIMIT;
           } else {
               long limit = sysconf(_SC_LINE_MAX);
               line_max = (limit < 0 || limit > MYLIMIT) ? MYLIMIT : (int)limit;
           }

           // line_max + 1 leaves room for the null byte added by fgets().
           line = malloc(line_max + 1);
           if (line == NULL) {
               // out of space
               ...
               return error;
           }

           while (fgets(line, line_max + 1, fp) != NULL) {
               // Verify that a full line has been read ...
               // If not, report an error or prepare to treat the
               // next time through the loop as a read of a
               // continuation of the current line.
               ...
               // Process line ...
               ...
           }
           free(line);
           ...

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.5, Standard I/O Streams, fgetc(), fopen(), fread(), fscanf(),
       getc(), getchar(), getdelim(), gets(), ungetc()

       The Base Definitions volume of POSIX.1-2017, <stdio.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                             FGETS(3)
