Trouble Passing array of Structs using pointers

Question

I'm having problems with a function that I use to write to an element of an array.

I think it might be because I'm not passing the array of struct correctly. I was wondering if someone can point out how to do this correctly. I've been screwing it up more than fixing it.

let's say I have a function menu.c I declare my struct newPerson person[MAX_PERSONS]; I then run my function addPerson(person, &num); which is the following

void addPerson(newPerson *pers, int *num){
    pers[*num] = (newPerson) {
                    "Michelle", "Leo", "6136458798", STUDENT,
                    .data = {.s = {9, 1234.50, 3}}
                };
    *num = *num + 1;
}

It runs, but won't print out correctly, I'm guessing because it doesn't write where I want it to pers[num]. I tried calling the function this way also addPerson(&person, &num); instead of just addPerson(person, &num); but then I receive this error

warning: passing argument 1 of ‘addPerson’ from incompatible pointer type [enabled by default]

and

note: expected ‘struct newPerson ’ but argument is of type ‘struct newPerson ()[20]’

I've tried changing the function to void addPerson(newPerson *pers[], int *num){ as well but nothing there. Was wondering if anyone can point out what I'm doing wrong here and how I can fix my problem. Any help would be appreciated, thanks!

Forgot to mention that the addPerson function works in some places where I run it.

int menu(int num) {
    newPerson person[MAX_PERSONS];
    //printf("THE NUMBER START OF MENU IS %d\n", num); test counter

    //addPerson(person, &num);    <- WRITES AND READS PROPERLY IF DONE HERE

    int option;
    printf(
            "\n\tPlease choose one of the following options to continue (0-9): ");
    scanf("%d", &option);


if (option == 1) { //program will ask for name input
    addPerson(person, &num);  <- HOWEVER IT DOES NOT WRITE OR READ PROPERLY HERE
    menu(num);
}

Both functions are called in menu.c However when I call addPerson in the if statement, it does not write/read properly.

Just solved the problem by declaring the struct as static! static newPerson person[MAX_PERSONS];

I'm not sure if this is taboo or anything, but it fixed my problem!

I'm going to make a wild guess that you are accessing person out of bounds. What's the value of num before you use in addPerson? — R Sahu
– R Sahu, Commented Feb 24, 2015 at 5:49
The problem is that the person array is a local variable, and you're calling the menu function recursively. — user3386109
– user3386109, Commented Feb 24, 2015 at 5:50

Akhil · Accepted Answer · 2015-02-24 09:43:47Z

1

By making static you have made the code inefficient as the memory for the data structure has been set aside regardless of whether it is needed or not while the program is executing.(With a static data structure, the size of the structure is fixed.)

Declare the function like

void addPerson(newPerson *pers[],int *num)

call the function like

void addPerson(newPerson *pers, int *num);

OR

void addPerson(newPerson pers[], int *num);

edited Feb 24, 2015 at 9:43

Akhil

1,0831 gold badge9 silver badges28 bronze badges

answered Feb 24, 2015 at 7:49

Mayavi

1496 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Mayavi Over a year ago

Declare the function like void addPerson(newPerson *pers[],int *num) call the function like void addPerson(newPerson *pers, int *num); OR void addPerson(newPerson pers[], int *num);

user1692517 · Accepted Answer · 2015-02-24 05:56:37Z

0

I was able to get it working by declaring the struct as static

static newPerson person[MAX_PERSONS];

Not sure if this is an actual fix or if it's just masking my problem though.

answered Feb 24, 2015 at 5:56

user1692517

1,1624 gold badges15 silver badges28 bronze badges

2 Comments

Vagish Over a year ago

What is value of MAX_PERSONS?Do you have sufficient stack space?

user3386109 Over a year ago

That's one way to fix the problem that the person array is a local variable. However, you still have a recursion problem. If the menu function calls itself, the stack will grow until there's a stack overflow and the program crashes. Without seeing more of the program, it's hard to advise how to fix the problem. Posting an MCVE would make this question much easier to answer.

Collectives™ on Stack Overflow

Trouble Passing array of Structs using pointers

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related