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



PPRROOLLOOGG
       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.

NNAAMMEE
       fgets -- get a string from a stream

SSYYNNOOPPSSIISS
       #include <stdio.h>

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

DDEESSCCRRIIPPTTIIOONN
       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 _f_g_e_t_s() function shall read bytes from _s_t_r_e_a_m 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 _f_g_e_t_s() function may mark the last data access timestamp of the
       file associated with _s_t_r_e_a_m for update. The last data access timestamp
       shall be marked for update by the first successful execution of
       _f_g_e_t_c(), _f_g_e_t_s(), _f_r_e_a_d(), _f_s_c_a_n_f(), _g_e_t_c(), _g_e_t_c_h_a_r(), _g_e_t_d_e_l_i_m(),
       _g_e_t_l_i_n_e(), _g_e_t_s(), or _s_c_a_n_f() using _s_t_r_e_a_m that returns data not
       supplied by a prior call to _u_n_g_e_t_c().

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

EERRRROORRSS
       Refer to _f_g_e_t_c().

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
   RReeaaddiinngg IInnppuutt
       The following example uses _f_g_e_t_s() 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 _s_y_s_c_o_n_f(_SC_LINE_MAX)
       returns -1 without setting _e_r_r_n_o.  This example assumes that
       _s_y_s_c_o_n_f(_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);
           ...

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       None.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._5, _S_t_a_n_d_a_r_d _I_/_O _S_t_r_e_a_m_s, _f_g_e_t_c(), _f_o_p_e_n(), _f_r_e_a_d(), _f_s_c_a_n_f(),
       _g_e_t_c(), _g_e_t_c_h_a_r(), _g_e_t_d_e_l_i_m(), _g_e_t_s(), _u_n_g_e_t_c()

       The Base Definitions volume of POSIX.1-2017, <<ssttddiioo..hh>>

CCOOPPYYRRIIGGHHTT
       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)
