How to sort an array of pointers by the addresses of what is inside the pointers

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hi I want to sort an array of pointers by the addresses of what is inside the pointers.
That is, the array holds a pointer within a particular cell within an array that contains strings.
Want to do this with the help of MERGE SORT
The array of pointer is char** ptr_to_chars_array

What I have tried:

C

void mergeSort(char* arr, int size)
{
	char* tmpArr = NULL;
	if (size <= 1)
		return;

	mergeSort(arr, size / 2);
	mergeSort(arr + size / 2, size - size / 2);
	tmpArr = (char*)malloc(size * sizeof(char));

	if (tmpArr)
	{
		merge(arr, size / 2, arr + size / 2, size - size / 2, tmpArr);
		for (int i = 0; i < size; i++)
		{
			arr+i = &tmpArr+i;
		}
		free(tmpArr);

		
	}
	else
	{
		printf("Memory allocation failure!!!\n");
		exit(1);	// end program immediately with code 1 (indicating an error)
	}
}

void merge(char* a1, int size1, char* a2, int size2, char* tmpArr)
{
	int ind1, ind2, tmpArrInd;
	ind1 = ind2 = tmpArrInd = 0;

	while ((ind1 < size1) && (ind2 < size2))
	{
		if (a1+ind1 >= a2+ind2)
		{
			tmpArr[tmpArrInd] = a1 + ind1;
			ind1++;
		}
		else {
			tmpArr[tmpArrInd] = a2 + ind2;
			ind2++;
		}
		tmpArrInd++;
	}

	while (ind1 < size1)
	{
		tmpArr[tmpArrInd] = a1 + ind1;
		ind1++;
		tmpArrInd++;
	}
	while (ind2 < size2) {
		tmpArr[tmpArrInd] = a2 + ind2;
		ind2++;
		tmpArrInd++;
	}
}

Posted 11-Mar-22 1:19am

Member 15562970

Updated 19-Jul-22 17:24pm

CPallini

v2

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Comments

OriginalGriff 11-Mar-22 8:10am

This is not a good question - we cannot work out from that little what you are trying to do.
Remember that we can't see your screen, access your HDD, or read your mind - we only get exactly what you type to work with - we get no other context for your project.

Perhaps an example of the input and output will help us understand exactly what you are trying to do, together with some explanation of what problem you are having with what code you already have?

Use the "Improve question" widget to edit your question and provide better information.

Richard MacCutchan 11-Mar-22 8:12am

Pointers are just numbers, so you sort them the same way you sort any other values.

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Member 15078716 · Answer 1 · 2022-07-19T17:24:00

He wants to sort some data.

He begins with, "hi I want to sort".

He later details that with, "Want to do this with the help of MERGE SORT".

- - - - - - - - - -

OK, here is MERGE SORT:

You could start with https://duckduckgo.com/?q=merge+sort+algorithm&t=h_&ia=web , which from my experience are a lot of links to the wrong way to do things.

So, I looked through them and found

Wikipedia has a nice article on mergesort at https://en.wikipedia.org/wiki/Merge_sort .
I suggest the Top-down implementation.

"A C++ program to Sort an array using merge sort algorithm", it seems OK.
https://www.simplilearn.com/tutorials/data-structure-tutorial/merge-sort-algorithm

There is a nice graphical representation, with pictures and easy to understand explainations at https://www.enjoyalgorithms.com/blog/merge-sort-algorithm .

There is a little more complicated graphical representation at https://www.tutorialspoint.com/data_structures_algorithms/merge_sort_algorithm.htm .

To bring all that together, there is another graphical explaination which might help you that you can find more about at https://www.geeksforgeeks.org/merge-sort/

Quoted from that page:

•    Declare left variable to 0 and right variable to n-1 
•    Find mid by medium formula. mid = (left+right)/2
•    Call merge sort on (left,mid)
•    Call merge sort on (mid+1,rear)
•    Continue till left is less than right
•    Then call merge function to perform merge sort.

Algorithm:

step 1: start
step 2: declare array and left, right, mid variable 
step 3: perform merge function.
        mergesort(array,left,right)
        mergesort (array, left, right)
        if left > right
        return
        mid= (left+right)/2
        mergesort(array, left, mid)
        mergesort(array, mid+1, right)
        merge(array, left, mid, right)
step 4: Stop

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