fgets(3p) — Linux manual page


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

PROLOG         top

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

NAME         top

       fgets — get a string from a stream

SYNOPSIS         top

       #include <stdio.h>

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

DESCRIPTION         top

       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(), getline(), gets(), or scanf() using stream that returns
       data not supplied by a prior call to ungetc().

RETURN VALUE         top

       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         top

       Refer to fgetc(3p).

       The following sections are informative.

EXAMPLES         top

   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 ...



RATIONALE         top




SEE ALSO         top

       Section 2.5, Standard I/O Streams, fgetc(3p), fopen(3p), fread(3p),
       fscanf(3p), getc(3p), getchar(3p), getdelim(3p), gets(3p), ungetc(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- 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 Standard 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)

Pages that refer to this page: stdio.h(0p)fgetc(3p)getdelim(3p)gets(3p)