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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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UNGETC(3P) POSIX Programmer's Manual UNGETC(3P)
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.
ungetc — push byte back into input stream
#include <stdio.h>
int ungetc(int c, FILE *stream);
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
fail.
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.
Upon successful completion, ungetc() shall return the byte pushed
back after conversion. Otherwise, it shall return EOF.
No errors are defined.
The following sections are informative.
None.
None.
None.
None.
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)
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)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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