mirror of https://github.com/mkerrisk/man-pages
121 lines
4.2 KiB
Plaintext
121 lines
4.2 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "FGETC" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" fgetc
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.SH NAME
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fgetc \- get a byte from a stream
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.SH SYNOPSIS
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.LP
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\fB#include <stdio.h>
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.br
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.sp
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int fgetc(FILE *\fP\fIstream\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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If the end-of-file indicator for the input stream pointed to by \fIstream\fP
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is not set and a next byte is present, the
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\fIfgetc\fP() function shall obtain the next byte as an \fBunsigned
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char\fP converted to an \fBint\fP, from the input stream
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pointed to by \fIstream\fP, and advance the associated file position
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indicator for the stream (if defined). Since \fIfgetc\fP()
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operates on bytes, reading a character consisting of multiple bytes
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(or "a multi-byte character") may require multiple calls to
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\fIfgetc\fP().
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.LP
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The
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\fIfgetc\fP() function may mark the \fIst_atime\fP field of the file
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associated with \fIstream\fP for update. The
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\fIst_atime\fP field shall be marked for update by the first successful
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execution of \fIfgetc\fP(), \fIfgets\fP(), \fIfgetwc\fP(), \fIfgetws\fP(),
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\fIfread\fP(), \fIfscanf\fP(), \fIgetc\fP(), \fIgetchar\fP(), \fIgets\fP(),
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or \fIscanf\fP() using \fIstream\fP that returns data not supplied
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by a prior call to \fIungetc\fP() or \fIungetwc\fP().
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIfgetc\fP() shall return the next byte
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from the input stream pointed to by \fIstream\fP. If the
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end-of-file indicator for the stream is set, or if the stream is at
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end-of-file, the end-of-file indicator for the stream shall be
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set and \fIfgetc\fP() shall return EOF. If a read error occurs, the
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error indicator for the stream shall be set, \fIfgetc\fP()
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shall return EOF, \ and shall set \fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIfgetc\fP() function shall fail if data needs to be read and:
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.TP 7
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.B EAGAIN
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The O_NONBLOCK flag is set for the file descriptor underlying \fIstream\fP
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and the process would be delayed in the \fIfgetc\fP()
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operation.
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.TP 7
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.B EBADF
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The file descriptor underlying \fIstream\fP is not a valid file descriptor
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open for reading.
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.TP 7
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.B EINTR
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The read operation was terminated due to the receipt of a signal,
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and no data was transferred.
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.TP 7
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.B EIO
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A
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physical I/O error has occurred, or the process is in a background
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process group attempting to read from its controlling terminal,
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and either the process is ignoring or blocking the SIGTTIN signal
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or the process group is orphaned. This error may also be
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generated for implementation-defined reasons.
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.TP 7
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.B EOVERFLOW
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The file is a regular file and an attempt was made to read at or beyond
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the offset maximum associated with the corresponding
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stream.
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.sp
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.LP
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The \fIfgetc\fP() function may fail if:
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.TP 7
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.B ENOMEM
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Insufficient storage space is available.
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.TP 7
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.B ENXIO
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A
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request was made of a nonexistent device, or the request was outside
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the capabilities of the device.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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If the integer value returned by \fIfgetc\fP() is stored into a variable
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of type \fBchar\fP and then compared against the
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integer constant EOF, the comparison may never succeed, because sign-extension
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of a variable of type \fBchar\fP on widening to
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integer is implementation-defined.
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.LP
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The \fIferror\fP() or \fIfeof\fP() functions must
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be used to distinguish between an error condition and an end-of-file
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condition.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIfeof\fP() , \fIferror\fP() , \fIfopen\fP() , \fIgetchar\fP() ,
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\fIgetc\fP() , the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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