GRASS GIS 8 Programmer's Manual 8.4.1(2025)-45ca3179ab
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segment/init.c
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1/****************************************************************************
2 *
3 * MODULE: segment
4 * AUTHOR(S): CERL
5 * Bernhard Reiter <bernhard intevation.de>,
6 * Brad Douglas <rez touchofmadness.com>,
7 * Glynn Clements <glynn gclements.plus.com>,
8 * Markus Neteler <neteler itc.it>,
9 * Markus Metz <markus.metz.giswork googlemail.com>
10 * PURPOSE: Segment initialization routines
11 * COPYRIGHT: (C) 2000-2009 by the GRASS Development Team
12 *
13 * This program is free software under the GNU General Public
14 * License (>=v2). Read the file COPYING that comes with GRASS
15 * for details.
16 *
17 *****************************************************************************/
18
19#include <stdio.h>
20#include <unistd.h>
21#include <string.h>
22#include <errno.h>
23#include <grass/gis.h>
24#include "local_proto.h"
25
26static int read_int(int, int *);
27static int read_off_t(int, off_t *);
28
29/* fd must be open for read and write */
30
31/**
32 * \fn int Segment_init (SEGMENT *SEG, int fd, int nseg)
33 *
34 * \brief Initialize segment structure.
35 *
36 * Initializes the <b>seg</b> structure. The file on <b>fd</b> is
37 * a segment file created by <i>Segment_format()</i> and must be open
38 * for reading and writing. The segment file configuration parameters
39 * <i>nrows, ncols, srows, scols</i>, and <i>len</i>, as written to the
40 * file by <i>Segment_format()</i>, are read from the file and stored in
41 * the <b>seg</b> structure. <b>nsegs</b> specifies the number of
42 * segments that will be retained in memory. The minimum value allowed
43 * is 1.
44 *
45 * <b>Note:</b> The size of a segment is <em>scols*srows*len</em> plus a
46 * few bytes for managing each segment.
47 *
48 * \param[in,out] SEG segment
49 * \param[in] fd file descriptor
50 * \param[in] nseg number of segments to remain in memory
51 * \return 1 if successful
52 * \return -1 if unable to seek or read segment file
53 * \return -2 if out of memory
54 */
55
56int Segment_init(SEGMENT *SEG, int fd, int nseg)
57{
58 SEG->open = 0;
59 SEG->fd = fd;
60 SEG->nseg = nseg;
61
62 if (lseek(fd, 0L, SEEK_SET) < 0) {
63 int err = errno;
64
65 G_warning("Segment_init: %s", strerror(err));
66 return -1;
67 }
68
69 /* read the header */
70 if (!read_off_t(fd, &SEG->nrows) || !read_off_t(fd, &SEG->ncols) ||
71 !read_int(fd, &SEG->srows) || !read_int(fd, &SEG->scols) ||
72 !read_int(fd, &SEG->len))
73 return -1;
74
75 return seg_setup(SEG);
76}
77
78static int read_int(int fd, int *n)
79{
80 int bytes_read;
81
82 if ((bytes_read = read(fd, n, sizeof(int))) == -1)
83 G_warning("read_int: %s", strerror(errno));
84
85 bytes_read = (bytes_read == sizeof(int));
86
87 return bytes_read;
88}
89
90static int read_off_t(int fd, off_t *n)
91{
92 int bytes_read;
93
94 if ((bytes_read = read(fd, n, sizeof(off_t))) == -1)
95 G_warning("read_off_t: %s", strerror(errno));
96
97 bytes_read = (bytes_read == sizeof(off_t));
98
99 return bytes_read;
100}
void G_warning(const char *msg,...)
Print a warning message to stderr.
Definition gis/error.c:203
int Segment_init(SEGMENT *SEG, int fd, int nseg)
Initialize segment structure.
int seg_setup(SEGMENT *SEG)
Internal use only.
SYMBOL * err(FILE *fp, SYMBOL *s, char *msg)