ungetc(3p) — Linux manual page


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

       ungetc — push byte back into input stream

SYNOPSIS         top

       #include <stdio.h>

       int ungetc(int c, FILE *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.1‐2017 defers to the ISO C standard.

       The ungetc() function shall push the byte specified by c
       (converted to an unsigned char) back onto the input stream
       pointed to by stream.  The pushed-back bytes shall be returned by
       subsequent reads on that stream in the reverse order of their
       pushing. A successful intervening call (with the stream pointed
       to by stream) to a file-positioning function (fseek(), fseeko(),
       fsetpos(), or rewind()) or fflush() shall discard any pushed-back
       bytes for the stream. The external storage corresponding to the
       stream shall be unchanged.

       One byte of push-back shall be provided. If ungetc() is called
       too many times on the same stream without an intervening read or
       file-positioning operation on that stream, the operation may

       If the value of c equals that of the macro EOF, the operation
       shall fail and the input stream shall be left unchanged.

       A successful call to ungetc() shall clear the end-of-file
       indicator for the stream. The value of the file-position
       indicator for the stream after all pushed-back bytes have been
       read, or discarded by calling fseek(), fseeko(), fsetpos(), or
       rewind() (but not fflush()), shall be the same as it was before
       the bytes were pushed back. The file-position indicator is
       decremented by each successful call to ungetc(); if its value was
       0 before a call, its value is unspecified after the call.

RETURN VALUE         top

       Upon successful completion, ungetc() shall return the byte pushed
       back after conversion. Otherwise, it shall return EOF.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top




RATIONALE         top




SEE ALSO         top

       Section 2.5, Standard I/O Streams, fseek(3p), getc(3p),
       fsetpos(3p), read(3p), rewind(3p), setbuf(3p)

       The Base Definitions volume of POSIX.1‐2017, stdio.h(0p)

COPYRIGHT         top

       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                        UNGETC(3P)

Pages that refer to this page: stdio.h(0p)fgetc(3p)fgetpos(3p)fgets(3p)fseek(3p)fsetpos(3p)stdin(3p)