/*
 * stdc-small-db.c - handle a small database file, with fixed-length records.
 * uses standard C library I/O functions, including fopen, fseek, fgetpos,
 * fsetpos etc.
 */

#include <stdio.h>              /* standard input/output routines.    */

#define RECORD_LEN 30		/* size of a record.                  */

/*
 * function: get_record. Reads a record from the given file.
 * input:    pointer to file stream, number of record in file (0 is 
 *           the first record), and a pointer to a buffer.
 * output:   '1' on success, '0' on failure. In case of success, the record
 *           is copied to the supplied buffer.
 */
int
get_record(FILE* file, long record_num, char* buf)
{
    long file_pos;    /* stores the original read/write pointer position. */
    int success = 0;  /* success/failure indicator. assume failure here.  */

    /* sanity checks */
    if (!file || record_num < 0 || !buf) {
        return 0;
    }

    /* note the current read/write pointer position.     */
    file_pos = ftell(file);
    if (file_pos < 0) {
        perror("get_record: ftell");
    }
    else {
        /* move to the record's location.                */
        if (fseek(file, record_num * RECORD_LEN, SEEK_SET) < 0) {
            perror("get_record: fseek");
        }
        else {
            /* read the record from the file stream.     */
            if (fread(buf, RECORD_LEN, 1, file) == 1) {
                success = 1;  /* mark that we succeeded in reading the record */
            }
	    else {
                perror("get_record: fread");
	    }

    	    /* restore the original read/write pointer position. */
    	    if (fseek(file, file_pos, SEEK_SET) < 0) {
                perror("get_record: fseek");
    	    }
        }
    }

    return success;
}

/*
 * function: put_record. Writes a record to the given file.
 * input:    pointer to file stream, number of the record in file (0 is
 *           the first record)  and a pointer to a buffer containing the
 *           data to be written.
 * output:   '1' on success, '0' on failure.
 */
int
put_record(FILE* file, long record_num, char* buf)
{
    long file_pos;    /* stores the original read/write pointer position. */
    int success = 0;  /* success/failure indicator. assume failure here.  */

    /* sanity checks */
    if (!file || record_num < 0 || !buf) {
        return 0;
    }

    /* note the current read/write pointer position.     */
    file_pos = ftell(file);
    if (file_pos < 0) {
        perror("put_record: ftell");
    }
    else {
        /* move to the record's location.                */
        if (fseek(file, record_num * RECORD_LEN, SEEK_SET) < 0) {
            perror("put_record: fseek");
        }
        else {
            /* write the record to the file stream.      */
            if (fwrite(buf, RECORD_LEN, 1, file) == 1) {
                success = 1;  /* mark that we succeeded in writing the record */
            }
	    else {
                perror("put_record: fwrite");
	    }

    	    /* restore the original read/write pointer position. */
    	    if (fseek(file, file_pos, SEEK_SET) < 0) {
                perror("put_record: ftell");
    	    }
        }
    }

    return success;
}

/*
 * function: main. write and read some records to/from a file.
 * input:    none.
 * output:   none.
 */
void
main()
{
    char* file_name = "small_db.data";
    char buf[RECORD_LEN];
    FILE* db_file;

    /* open the database file, in read and write mode. */
    db_file = fopen(file_name, "w+");
    if (!db_file) {
	perror("fopen");
	exit(1);
    }

    /* write some records into the database file.    */
    strcpy(buf, "hello world");
    put_record(db_file, 5, buf);
    strcpy(buf, "adios, amigos");
    put_record(db_file, 17, buf);
    strcpy(buf, "marchaba marchabtain");
    put_record(db_file, 12, buf);

    /* now read some records from the database file. */
    get_record(db_file, 17, buf);
    printf("record %d: '%s'\n", 17, buf);
    get_record(db_file, 5, buf);
    printf("record %d: '%s'\n", 5, buf);
    get_record(db_file, 3, buf); /* never written - should be garbage */
    printf("record %d: '%s'\n", 3, buf);

    if (fclose(db_file) == EOF) {
	perror("fclose");
	exit(1);
    }
}