Thread: Database Program

Hi,

I am currently working on a database program that has a menu, giving the user the following options: Enter data, Edit data, Delete data, Display data, Save data, Load data and Quit.

At the moment, i have only started working on the enter and display data functions. I've found that entering the data works ok, but the program fails to display this data when selected in the menu. Here is the current code:

Code:

/* By Luke Sowersby */

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

struct Details get_details(int);
void print_details(struct Details);
int file_save(int, char [], struct Details *);
int file_load(char [], struct Details *);
void delete_details (int position,struct Details *fileptr);
void edit_details (int position,struct Details *fileptr);

struct Details
    {
    char surname[20];
    char forename[20];
    char address[20];
    int telephone;
    char email[20];
    };

int main (void)
{
unsigned s;
struct Details *p;
int position=0;
int option;

printf("How many sets of details?\n");
scanf("%u",&s);

if((p=(struct Details *)malloc(s * sizeof(struct Details)))==NULL)
    {
    printf("Cannot allocate %u bytes",s);
    getch();
    return 1;
    }

do
    {
    printf("\nPlease select one of the following options for the data:\n1. Enter\n2. Edit\n3. Delete\n4. Display\n5. Save\n6. Load\n7. Quit\n");
    scanf("%d",&option);
    switch(option)
        {
        case 1:
            printf("\nS=%d, position=%d",s,position);
            if (position<=(s-1))
                {
                get_details(position);
                position++;
                }
            else
                {
                printf("\nMemory full");
                }
            break;
        case 2:
            edit_details(position,p);
            break;
        case 3:
            delete_details(position,p);
            break;
        case 4:
            print_details(p[position]);
            break;
        case 5:
            file_save(s,"datafile.txt",p);
            break;
        case 6:
            s=file_load("datafile.txt",p);
            position=s;
            break;
        case 7:
            printf("\nExit");
            break;
        };
    }

while(option!=7);

printf("\n\nHit a key");
getch();
free(p);
return 0;
}


struct Details get_details(int position)
{
struct Details get_member;

printf("\nDetails for class member %d",position+1);
printf("\nEnter the forename of the member: ");
scanf("%s",get_member.forename);
printf("\nEnter the surname of the member: ");
scanf("%s",get_member.surname);
printf("\nEnter the street address of the member: ");
scanf("%s",get_member.address);
printf("\nEnter the telephone number of the birth of the member: ");
scanf("%d",&get_member.telephone);
printf("\nEnter the email of the member: ");
scanf("%s",get_member.email);

return get_member;
}

void print_details(struct Details print_member)
{
printf("\n %s %s %s %d %s",print_member.forename,print_member.surname,print_member.address,print_member.telephone,print_member.email);
}

int file_save(int size,char filename[],struct Details *fileptr)
{
int i;
FILE *fptr;
if((fptr=fopen(filename,"wb"))==NULL)
    {
    printf("File cannot be opened\n");
    exit(1);
    return 0;
    }
fwrite(fileptr,sizeof(struct Details),size,fptr);
fclose(fptr);
return 1;
}

int file_load(char filename[],struct Details *fileptr)
{
FILE *fptr;
int size;
if((fptr=fopen(filename,"rb"))==NULL)
    {
    printf("File cannot be opened\n");
    exit(1);
    return 0;
    }
fread(fileptr,sizeof(struct Details),size,fptr);
fclose(fptr);
return 1;
}

void delete_details (int position,struct Details *fileptr)
{
int file_load(char filename[],struct Details *fileptr);
}

void edit_details (int position,struct Details *fileptr)
{
int file_save(int size,char filename[],struct Details *fileptr);
}

I've highlighted the key areas which i think may be causing this problem.

Please not, i have not started working with other options yet, and i have only placed the current code in those functions so i could compile it.

Can anyone provide some help please?

Thanks.

position is probably not a valid number when you try to print -- I expect it will be one after all the data you just entered.

Managed to fix it. The code for case 4 was incorrect. Here is the new code for this:

Code:

case 4:
            for (position=0;position<s;position++)
                {
                print_details(p[position]);
                }

No doubt i'll have further problems later on...

1. The problem I see with your file_load is that if you should manage to open the file, you are going to try to read an unknown number of records (possibly negative!) from the file. You have to know how many to read before you start. Do you see a datafile.txt file in your directory when you run the program?

2. As to deleting data, you have to overwrite the old file with a new file that does not contain the bits you want to delete.

Originally Posted by tabstop

1. The problem I see with your file_load is that if you should manage to open the file, you are going to try to read an unknown number of records (possibly negative!) from the file. You have to know how many to read before you start. Do you see a datafile.txt file in your directory when you run the program?

2. As to deleting data, you have to overwrite the old file with a new file that does not contain the bits you want to delete.

datafile.txt is in my directory, and updates perfectly well when i choose to save. I'll experiment with it tomorrow. Thanks for the help.