CODEWITHSUNDEEP
cpointersmatrix
Mets_CS11
Mets_CS11

Reputation: 99

Is there a best practice for allocating memory in C?

I've been trying to make a function that appends matrix B onto Matrix A by making a new combined matrix. The first function I created passes a pointer (that was declared in main()) to the function which then works up the pointer to add values. This worked. However, I am also trying a different method by using malloc() within the function to define a pointer so that the function is more portable and dyanmic. However, when I try to print the final values in the final matrix I am getting undefined behavior.

Here is the included function from the created header file.

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

  int *fAddArrays(int *A, int *B, int a, int b)
{
    
    int *O;
    O = (int *) malloc((a+b) * sizeof(int));
    
    int c;
    int d;
    
    for (c = 0; c < a; c++)
    {
        *O = *A;
        A++;
        O++;
        
    }
    
    for (d = 0; d < b; d++)
    {
        *O = *B;
        B++;
        O++;
    }
    
    
        return O;
}

Here is the use of the function in main()

#include <stdio.h>
#include <unistd.h>
#include "CustomArray.h"
#include <stdlib.h>


int main(void)

{
    int A[5] = {1,2,3,4,5};
    int B[7] = {6,7,8,9,10,11,12};
    int a = 5;
    int b = 7;
    int c = a + b;
    int x = 0;
    int NewArray[c], *ArrayPtr;
    
    ArrayPtr = fAddArrays(A,B,a,b);

    for( x = 0; x < c; x++)
    {
        *(NewArray + x) = *ArrayPtr;
        
        printf("Value of NewArray[%d] = %d\n", x, *ArrayPtr);
        sleep(1);
        
        ArrayPtr++;
    }
    
    
    
    return 0;
}

Upvotes: 0

Views: 92

Answers (1)

Michael Anderson
Michael Anderson

Reputation: 73600

Your problem is that you increment O and then return it.

You need to save away the original value and increment a copy.

int *fAddArrays(int *A, int *B, int a, int b) {

    int * original = (int *) malloc((a+b) * sizeof(int));
    int * p = original;

    for (int c = 0; c < a; c++) {
        *p = *A;
        A++;
        p++;
    }

    for (int d = 0; d < b; d++) {
        *p = *B;
        B++;
        p++;
    }

    return original;
}

Upvotes: 2

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