C++ C Arrays Pointers Reference

Sorting an Array of Double Pointers in C/C++

Sorting can be a tricky endeavor, especially when dealing with pointers and multi-level data structures in programming languages like C and C++. One common challenge programmers face is sorting an array of double pointers based on the values they point to. This has prompted many to seek an effective solution that not only sorts the values correctly but does so in an efficient manner.

Understanding the Problem

When given an array of double pointers (e.g., int **pArray), each pointer in this array points to another pointer that ultimately points to an integer value. The task at hand is to sort this array by the dereferenced integer values it points to, effectively reordering the array of pointers based on the actual numeric values.

The Solution

To solve this, we will implement a function called SortArray. Below is the refined approach that ensures the array of double pointers is sorted correctly:

Code Implementation

void SortArray(int **pArray, int ArrayLength) {
    int i, j, flag = 1;    // Set flag to 1 to begin initial pass
    int *temp;             // Holding variable for swapping
    
    for(i = ArrayLength - 1; i > 0 && flag; i--) {
        flag = 0;          // Reset flag for the new inner loop
        for (j = 0; j < i; j++) {
            // Compare the dereferenced values for ascending order
            if (*pArray[j] > *pArray[j + 1]) {  
                // Swap the pointers if they are in the wrong order
                temp = pArray[j];             
                pArray[j] = pArray[j + 1];
                pArray[j + 1] = temp;
                flag = 1;   // Indicates that a swap occurred
            }
        }
    }
}

Code Breakdown

  1. Initialization:

    • We start by defining indices i and j for iteration. The flag variable indicates whether any swaps were made during a pass.

  2. Outer Loop:

    • The outer loop (for(i = ArrayLength - 1; i > 0 && flag; i--)) runs as long as there are elements to compare. It helps to reduce unnecessary comparisons in subsequent passes.

  3. Inner Loop:

    • The inner loop (for(j = 0; j < i; j++)) iterates through the array of pointers, comparing the values they point to by dereferencing.

  4. Conditional Swapping:

    • If the value pointed to by the current pointer is greater than the next, we swap the pointers using a temporary variable.

  5. Efficiency:

    • The usage of the flag optimizes the process by breaking out of the loop early if no swaps are made, indicating that the array is sorted.

Additional Tips

  • Understanding Sorting Algorithms:

    • If you’re interested in learning more about sorting algorithms, check out a great resource on Bubble Sorting, which elaborates on fundamental concepts of sorting.

  • Practice Makes Perfect:

    • Experiment with variations of this function by altering the sorting criteria (e.g., sorting in descending order) to deepen your understanding.

Conclusion

Sorting an array of double pointers in C/C++ can seem daunting at first, but with a clear understanding of dereferencing pointers and a structured approach, it’s manageable. This guide provided you with a practical solution and the rationale behind it, so you can apply these concepts in your own projects with confidence.