3xxx3

/* Failas: manbar3_rw01.c */

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>

int mb_open( const char *name, int flags, mode_t mode );
void mb_close( int fd );

void mb_close( int fd ){
   if ( close( fd ) != 0 )
        perror ( "close() failed" );
}

int mb_open( const char *name, int flags, mode_t mode ){
    int dskr;
   dskr = open( name, flags, mode );
   if( dskr == -1 ){
      perror( "open() failed" );
      exit(1);
   }
   return dskr;
}

int main( int argc, char * argv[] ){
    int r_dskr;
    char *end;
    char *data;
    struct stat sbuf;
    int offset;
    printf( "(C) 2016 Mantas Bartkus, %s\n", __FILE__ );

    if ( argc != 3 ){
        fprintf(stderr,  "Usage: %s failas pozicija_faile\n", argv[0] );
        exit(1);
    }

    if ( stat(argv[1], &sbuf) == -1 ) {
        perror("stat failed");
        exit(1);
    }

    offset = (int) strtol( argv[2], &end, 10 );

    if ( *end ){
        perror( "Second parameter must be a number" );
        exit(1);
    }

    if ( offset < 0 || offset > sbuf.st_size-1 ) {
        fprintf( stderr, "offset must be in the range 0-%ld\n",
                                    sbuf.st_size-1 );
        exit(1);
    }


    r_dskr = mb_open( argv[1], O_RDONLY , 0 );

    data = mmap((caddr_t)0, sbuf.st_size, PROT_READ, MAP_SHARED, r_dskr, 0);

    if (data == (caddr_t)(-1)) {
        perror("mmap() failed");
        exit(1);
    }

    printf("byte at offset %d is '%d'\n", offset, (int) data[offset]);

    if ( munmap( data, sbuf.st_size ) != 0 ){
        perror( "munmap() failed" );
        exit(1);
    }

    mb_close( r_dskr );
    return 0;
}