segment/get_row.c

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#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <grass/segment.h>


int segment_get_row(const SEGMENT * SEG, void *buf, int row)
{
    int size;
    int ncols;
    int scols;
    int n, index, col;

    ncols = SEG->ncols - SEG->spill;
    scols = SEG->scols;
    size = scols * SEG->len;

    for (col = 0; col < ncols; col += scols) {
        segment_address(SEG, row, col, &n, &index);
        if (segment_seek(SEG, n, index) < 0)
            return -1;

        if (read(SEG->fd, buf, size) != size) {
            G_warning("segment_get_row: %s", strerror(errno));
            return -1;
        }

        /* The buf variable is a void pointer and thus points to anything. */
        /* Therefore, it's size is unknown and thus, it cannot be used for */
        /* pointer arithmetic (some compilers treat this as an error - SGI */
        /* MIPSPro compiler for one). Since the read command is reading in */
        /* "size" bytes, cast the buf variable to char * before incrementing */
        buf = ((char *)buf) + size;
    }
    if ((size = SEG->spill * SEG->len)) {
        segment_address(SEG, row, col, &n, &index);
        if (segment_seek(SEG, n, index) < 0)
            return -1;

        if (read(SEG->fd, buf, size) != size) {
            G_warning("segment_get_row: %s", strerror(errno));
            return -1;
        }
    }

    return 1;
}