Thread: Help With fseek();

Hello, I'm having problems learning about rand access files...

Most of my code works, all until you get to the fseek. The output is all garbaled, I'm not sure why.

I'll post the entire code, so that if it's something other than the fseek that is affecting it, you could point that out...

Thanks

Code:

 #include <stdio.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>

#define PASS1 "daniel"
#define PASS2 "pword24"
#define INVARY 10
#define TRANS 1000

struct inventory {
    char desc[25];
    int invCode;
    int invAmount;
    float invPrice;
};

struct transaction {
    char desc[25];
    int invCode;
    int invAmount;
    float invPrice;
};

void printInfo(struct inventory inv_db_new);

FILE * disk_file;

main()
{
    //Variables
    int counter;
    //Create arrays of the stuctures
    struct inventory inv_db[INVARY] = {{"Widget", 1001, 10, 2.95},
                                       {"Widget2", 1002, 10, 5.20},
                                       {"Widget3", 1003, 10, 10.00},
                                       {"Widget4", 1004, 10, 4.56},
                                       {"Widget5", 1005, 10, 9.99},
                                       {"Widget6", 1006, 10, 4.44},
                                       {"Widget7", 1007, 10, 70.02},
                                       {"Widget8", 1008, 10, 45.66},
                                       {"Widget9", 1009, 10, 34.55},
                                       {"Widget10", 1010, 10, 30.23}};
    
    struct inventory inv_db_new[INVARY];
    struct inventory aVar;
    struct transaction trans_db[TRANS];
    
    disk_file = fopen("c:\\may.inv", "w+");
        if (!disk_file) {
        printf("Error, with disk\n");
        }
    printf("Success, with disk\n");
    fwrite(inv_db, sizeof(inv_db), 1, disk_file);
    printf("Success in writing to disk\n");
    fclose(disk_file);
    
    disk_file = fopen("c:\\may.inv", "r+");
        if (!disk_file) {
        printf("Error, with disk\n");
        }
    fread(inv_db_new, sizeof(inv_db_new), 1, disk_file);
    for (counter = 0; counter < INVARY; counter++) {
    printInfo(inv_db_new[counter]);
    }
    fclose(disk_file); 
    
    disk_file = fopen("c:\\may.inv", "r+");
        if (!disk_file) {
        printf("Error, with disk\n");
        }
    
    fseek(disk_file, (4L * sizeof(aVar)), SEEK_SET);
    fread(&aVar, sizeof(aVar), 1, disk_file);
    printInfo(aVar); 
    fclose(disk_file);    
}

void printInfo(struct inventory str_nam)
{
    printf("\n%d ", str_nam.invCode);
    printf("%s ", str_nam.desc);
    printf("%d ", str_nam.invAmount);
    printf("$%.2f\n", str_nam.invPrice);
    return;
}

the trouble you're experiencing is being caused by the way you are opening the files. You are using the r+ and w+ ways of opening files (and these methods are used for "updating" files...or something like that)

The type of read/write style you're looking for in this case is "rb" and "wb" for read/write binary.

Code:

fopen("c:\\may.inv", "r+");

change that to:

Code:

fopen("c:\\may.inv", "rb");

and do the same with the w+ one, change it to a wb

hope that helps....

don't forget to exit your program when it doesn't open correctly. You warn them but don't quit