fgets(3posix) [posix man page]

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

NAME

       fgets - get a string from a stream

SYNOPSIS

       #include <stdio.h>

       char *fgets(char *restrict s, int n, FILE *restrict stream);

DESCRIPTION

       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. The string is then terminated with a null byte.

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

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 each line of input.  {LINE_MAX}, which defines the maximum size of the input line, is defined in
       the <limits.h> header.

	      #include <stdio.h>
	      ...
	      char line[LINE_MAX];
	      ...
	      while (fgets(line, LINE_MAX, fp) != NULL) {
	      ...
	      }
	      ...

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       fopen() , fread() , gets() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .

IEEE
/The Open Group						       2003								  FGETS(P)

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

PROLOG

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

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.1-2008 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. The string is then terminated with a null byte.

       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(), get-
       line(), 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() can't 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.1-2008, <stdio.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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						       2013								 FGETS(3P)