How to Initialize a database from a header file or c type file

Question

I'm working on an assignment of creating a "cat" database using a struct to record the name, gender, weight etc. of cats using C. I have made a few header files below:

Cat.h

#pragma once

#include <stdint.h>

const int MAX_CAT_NAME = 50;

enum Gender {
    MALE,
    FEMALE,
    UNKNOWN
};

struct Cat{

    char name[MAX_CAT_NAME + 1];
    Gender gender = UNKNOWN;
    float weightInPounds = 0.01;
    uint32_t chipId = 0;
    bool isFixed = false;
};

ArrayDB.h

#pragma once

#include "Cat.h"

#define MAX_CATS 100

extern Cat catArray[ MAX_CATS ];

extern int* numCats;

and ArrayDB.c

#include "ArrayDB.h"
#include "Cat.h"

Cat catArray[ MAX_CATS ];

void initDB() {
    *numCats = 0;

    for( int i = 0; i < MAX_CATS; i++ ) {
        Cat Cat = generateCat();
        if( validateCat(&Cat) ) {
            catArray[ numCats++ ] = Cat;
        }
    }

}

There is also a Cat.c file I have linked with struct Cat to generate the cat's name, validate the cat and print the cat, but I'm not sure if it is needed to initialize the database

In my assignment instructions, I was told for the header file, ArrayDB.h:

Declare the max size of the cat array as MAX_CATS in ArrayDB.h
Declare a cat array in ArrayDB.h
Declare the current array size as numCats in ArrayDB.h

I've done this, but I'm stuck on the next step for ArrayDB.c: "Define all three declarations in ArrayDB.c (I hope I've done this correctly) and write a function called initDB in ArrayDB.c to initialize the database." The return type and parameters were left up to me, so I just used a void function.

In my code for ArrayDB.c, I've attempted to call the functions that I've written from Cat.c (That also uses variables from struct Cat) to initialize the "cat" database, but I have compilations errors in ArrayDB.c that say generateCat and validateCat() are undeclared. I thought if I included the header file from Cat.h, I'd be able to initialize the database, but I think this isn't how I can do this.

Can someone show me how I can initialize the database in my function void initDB()?

I thought I can do it with my header files, but I'm not sure now.

I can paste my Cat.c code if it's needed. I would appreciate any guidance.

Related (possible duplicate): [How to initialize a struct in accordance with C programming language standards](https://stackoverflow.com/questions/330793/how-to-initialize-a-struct-in-accordance-with-c-programming-language-standards). Note that you should not put executable code in a header file. — Weather Vane, Feb 26 '23 at 12:17
`numCats` should have an integer type, not a pointer type. It's supposed to be a number, giving the current number of cats. Why would you make it a pointer? — Tom Karzes, Feb 26 '23 at 14:01
I would take exception to the task "Declare the max size of the cat array as MAX_CATS in ArrayDB.h" You need to clearly understand the difference between a declaration and a definition, and this task blurs the meaning of the words. They are probably asking you to use the pre-processor to #define MAX_CATS, but MAX_CATS is not being "declared" in the usual sense. Variable definitions and pre-processor macro definitions are very different things, and it seems very strange to use the word "declare" here. — William Pursell, Feb 26 '23 at 14:10
You have made `#define MAX_CATS 100` but it says to declare it in the header and define it in the source file so you can't use a `#define` to set it - you need to make it a const int like you did with `const int MAX_CAT_NAME = 50;` — Jerry Jeremiah, Feb 26 '23 at 20:58

Allan Wind · Accepted Answer · 2023-02-27T16:58:56.553

In C you initialize variables (instance of a type) not the type struct Cat which is syntax error. You also want to use a symbolic constants (#define) instead of a const variable. You are missing typedefs for Gender and Cat to be able to use them the way you do.

I suggest you avoid using global variables so you define your database in main() instead:

If you generate an instance of struct Cat there should be no need to validate them.

#include <stdint.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX_CATS 100
#define MAX_CAT_NAME 50

enum Gender {
    MALE,
    FEMALE,
    UNKNOWN
};

struct Cat {
    char name[MAX_CAT_NAME + 1];
    enum Gender gender;
    float weightInPounds;
    uint32_t chipId;
    bool isFixed;
};

void initDB(struct Cat cats[MAX_CATS]) {
    for(size_t i = 0; i < MAX_CATS; i++ )
        cats[i] = (struct Cat) { "", UNKNOWN, 0.01, 0, 0 };
}

int main() {
    struct Cat cats[MAX_CATS];
    initDB(cats);
}

How to Initialize a database from a header file or c type file

1 Answers1