Thread: function pointers and header files and such

Okay, so I'm a rather green c programmer here. I need some help with header files. What goes where etc. As I think that's the reason this won't compile. I'll give you the code and hopefully you'll understand what it is I'm trying to do here. Basically I've been given an assignment to used function pointers, but no real direction other than "use function pointers for datatype functions". So this was my idea, wrap the handing of records into another struct with function pointers that do all the work of managing array operations etc.

data.h

Code:

typedef struct record
{
    char name[40];
    int logins;
    int time;
} record;


typedef struct data
{
    int size;
    int count = 0;
    record * arr;

    void (*init) (data *,int);
    init = &initFunc;

} data;

void initFunc (data *,int);

data.c

Code:

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

#include "data.h"

void initFunc (data *foo, int size)
{
    foo.arr = (record *) malloc(sizeof(record)*size);
    foo.size = size;
}

in main.c

Code:

.
.
.
data foo;
foo.init(&foo,8);
.
.
.

Code:

    void (*init) (data *,int);
    init = &initFunc;

That's the part that does not compile is it not? You'd really have to assign yrinstanceofthestruct.init = &initfunc every time you make an instance of yr struct to make that work (annoying). It doesn't make all that much sense to do this in your situation, it would be easier to just say init(&foo, 8) (like passing this pointer in c++).

Something where a function pointer as a member might be useful is if you had some data pointed to by another member void * that needed to be sorted, and then you would sort it using the function assigned to the function pointer. This is the premise of the library function qsort basically.

If you can think of a situation where it might be useful to be able to customize what function is being called to respond to whatever is happening. A function which reads data from a file might want a function pointer to a function which would be processing the data that is being read from the file in a custom manner.

Guess I should have been more specific, apologies.

Here's the compiler output:

Code:

data.h:12: warning: no semicolon at end of struct or union
data.h:12: error: syntax error before '=' token
data.h:15: error: syntax error before '*' token
data.h:17: warning: type defaults to `int' in declaration of `data'
data.h:17: warning: data definition has no type or storage class
data.h:19: error: syntax error before '*' token
last_sort.c: In function `main':
last_sort.c:34: error: syntax error before "foo"
last_sort.c:35: error: `foo' undeclared (first use in this function)
last_sort.c:35: error: (Each undeclared identifier is reported only once
last_sort.c:35: error: for each function it appears in.)

This is the reason I thought it was just how I had the files set up or something. But you didn't mention anything wrong with how I structured my code.

In any case, I know the use of function pointers this way is useless but that's how the assignment reads. I have to use function pointers for all datatype functions other than init type stuff.

I did change that, but it didn't help. The compiler is still giving the same errors. Line 14 being "int count = 0;"

Oh gee, that makes sense. Now I feel rather stupid. I got it to compile now. Thanks.