Thread: return array from function

Hi,

I'm currently doing the following in my app

Code:

int funcGetArrayLength()
return len

char *arr[len]

I then need to perform some actions on this newly created array using another function. Is the best way forward returning an array that I can copy into my original? Any responses greatly appreciated.

Thanks

You are aware that its an array of pointers yes?

Some implementations, edit the array as a argument;

eg

Code:

void foo(char * array)
{
    array[0] = 'a';
    return;
}

But perhaps providing a better example of what your trying to do could help?

Not sure what you're really doing in your code, but if you're talking about creating an array inside of a function and trying to return it, here are a few words on the subject.

First of all, returning an array is basically just returning a pointer to the first element.

Right:

Code:

int *createArray(int iLength)
{
	int *array = malloc(iLength * sizeof(*array)); /* Make sure it's dynamic memory,
                                             NOT local to the function! */
	return array;
}

malloc() has not been casted as a favor to those that freak out over it.

WRONG:

Code:

int *createArray(int iLength)
{
	int array[iLength]; /* WRONG WRONG WRONG */
	return array; /* WRONG WRONG WRONG */
}

The reason the last example is wrong is because local variables are destroyed upon the return of the function. In the first example, the memory was located from the heap while local variables are allocated on the stack.

Edit: Corrected mistake, missing sizeof(). My sincerest apologies.

> int *array = malloc(iLength * (*array));
You mean
int *array = malloc(iLength * sizeof(*array));

I knew I should have gotten some sleep. Yes, you are correct, as usual. My sincerest apologies.

Well it's kinda silly doing it that way... Why not just have one function that does all of that ? :|

Yes well now that I know how to return an array I'll definitely do that. It also seems like twice the work searching the directory twice (once for the size of the array and then again to store the filenames). Can I do this dynamically by only searching the dir once??

Don't expect you to do my homework.....but if it's possible (and not too involved) I'd love to know..

Yes, you can do that. I wrote a function just recently that did something similar.

Here's a general idea:

1) Create an array of an initial size.
2) In a loop, read an element (file name in your case?) and stick it in the array.
3) If you run out of memory in your array, call realloc() and make it bigger. If realloc() fails, you pretty much ran out of memory in your system.
4) If you run out of elements, you're done.
5) Call realloc() to resize the array to trim off any extra space. Optional if you're more concerned about performance instead of memory.

Perhaps a struct, with a linked list?

Code:

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

#define MAXPATH 260

struct filenode_t {
	struct filenode * next;
	char FileName[MAXPATH];
} filenode;

struct contents_t {
	struct filenode * f;
} contents;

int GetDirContents(struct contents * c);

int main(void)
{
	int files = 0;
	struct contents * c;

	files = GetDirContents(c);

	// remember to free the linked list!
	return 0;
}

int GetDirContents(struct contents * c)
{
	int nFiles = 0;		// num of files found

	// scan / malloc directory contents...

	// if it fails return -1 files ? (So you know it failed??)- upto you.

	return nFiles;
}

Dunno if this is the best way to do it?

*mutters something about this very scenario being in the FAQ*