156 lines
4.3 KiB
Groff
156 lines
4.3 KiB
Groff
.\" $NetBSD: fgetln.3,v 1.14 2004/05/10 17:15:28 drochner Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)fgetln.3 8.3 (Berkeley) 4/19/94
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.\"
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.Dd April 21, 2004
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.Dt FGETLN 3
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.Os
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.Sh NAME
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.Nm fgetln
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.Nd get a line from a stream
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft char *
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.Fn fgetln "FILE * restrict stream" "size_t * restrict len"
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.Sh DESCRIPTION
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The
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.Fn fgetln
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function
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returns a pointer to the next line from the stream referenced by
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.Fa stream .
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This line is
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.Em not
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a C string as it does not end with a terminating
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.Dv NUL
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character.
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The length of the line, including the final newline,
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is stored in the memory location to which
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.Fa len
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points.
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(Note, however, that if the line is the last
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in a file that does not end in a newline,
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the returned text will not contain a newline.)
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.Sh RETURN VALUES
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Upon successful completion a pointer is returned;
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this pointer becomes invalid after the next
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.Tn I/O
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operation on
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.Fa stream
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(whether successful or not)
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or as soon as the stream is closed.
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Otherwise,
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.Dv NULL
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is returned.
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The
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.Fn fgetln
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function
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does not distinguish between end-of-file and error; the routines
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.Xr feof 3
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and
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.Xr ferror 3
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must be used
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to determine which occurred.
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If an error occurs, the global variable
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.Va errno
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is set to indicate the error.
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The end-of-file condition is remembered, even on a terminal, and all
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subsequent attempts to read will return
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.Dv NULL
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until the condition is
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cleared with
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.Xr clearerr 3 .
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.Pp
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The text to which the returned pointer points may be modified,
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provided that no changes are made beyond the returned size.
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These changes are lost as soon as the pointer becomes invalid.
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.Sh ERRORS
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.Bl -tag -width [EBADF]
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.It Bq Er EBADF
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The argument
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.Fa stream
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is not a stream open for reading.
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.El
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.Pp
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The
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.Fn fgetln
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function
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may also fail and set
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.Va errno
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for any of the errors specified for the routines
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.Xr fflush 3 ,
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.Xr malloc 3 ,
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.Xr read 2 ,
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.Xr stat 2 ,
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or
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.Xr realloc 3 .
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.Sh SEE ALSO
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.Xr ferror 3 ,
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.Xr fgets 3 ,
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.Xr fopen 3 ,
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.Xr putc 3
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.Sh HISTORY
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The
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.Fn fgetln
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function first appeared in
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.Bx 4.4 .
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.Sh CAVEATS
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Since the returned buffer is not a C string (it is not null terminated), a
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common practice is to replace the newline character with
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.Sq \e0 .
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However, if the last line in a file does not contain a newline,
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the returned text won't contain a newline either.
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The following code demonstrates how to deal with this problem by allocating a
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temporary buffer:
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.Bd -literal
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char *buf, *lbuf;
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size_t len;
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lbuf = NULL;
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while ((buf = fgetln(fp, &len))) {
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if (buf[len - 1] == '\en')
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buf[len - 1] = '\e0';
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else {
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if ((lbuf = (char *)malloc(len + 1)) == NULL)
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err(1, NULL);
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memcpy(lbuf, buf, len);
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lbuf[len] = '\e0';
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buf = lbuf;
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}
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printf("%s\en", buf);
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if (lbuf != NULL) {
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free(lbuf);
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lbuf = NULL;
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}
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}
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.Ed
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