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PO"Dynamic (pointer) arrays" across functions
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copied!<p>I wish to create a function which returns all the possible numbers a number can be divided by. Also I wish to use these returned results in another function which looks for all the prime numbers in those results and in turn returns those.</p> <p>Long story short, I want to be able to return "dynamic arrays" and use them again in another function.</p> <p>What I have so far:</p> <pre><code>int *division (long a) { int i; int *divResult = malloc(a * sizeof(long)); //Ultimately I want to allocate space dynamically instead of reserving too much space if (naturalNumber(a)) { //What it basically does is "fmod(a, 1)" (returns boolean) divLength = 0; //A global int set to trace the length of division() for (i = 0; i < a + 1; i++) { if (divisor(i, a)) { //Checks wether the division of a by i returns a whole number (returns boolean) //divResult = realloc(divResult, sizeof(long)); //This gives seg faults and errors durning runtime; To be clear I am not exactly using it like this. What I do is I adjust the "malloc(a*sizeof(long))" to "malloc(sizeof(long))" divResult[i] = i; //If i is a divisor add it to the pointer divLength += 1; //track how long the current division is } } } free(divResult); //I was hoping this to remove the divResult from the memory, sadly it is still there and doesnt give me an error of me trying to return a NULL value //printf("Mem: %p\n", (void *)divResult); return divResult; //Return a "dynamic array" so that another function can use it } </code></pre> <p>As you can see, I am aware of the fact that i have to use pointers instead of real arrays because those cannot be returned. I know this works and has returned true values.</p> <p>Also I want this function to use the division() function to see the divisors of a number and put them in an array:</p> <pre><code>int *primes (long a) { //I'm trying to reuse the same tactic as before: int i; int *primeResult = malloc(a * sizeof(long)); //Allocating it again... if (naturalNumber(a)) { //See previous codeblock for (i = 0; i < a + 1; i++) { division(i); //Calling the function here to divide each number from 1 to "a" so I am able to see which one is of size 2 (in other words the division of number *1 to a* and check wether it is a prime number (it has in total only 2 divisors)) printf("len = %d\n", divLength); //prints the current length of division() if (divLength == 2) { //If the division() "length" is 2 primeResult[i] = i; //add i to primes } } } free(primeResult); //Same as above return primeResult; } </code></pre> <p>As you might guess I'm not getting the expected results.</p> <p>Using:</p> <pre><code>int *div; div = division(a) + 1; for (i = 0; i < a; i++) { if (*(div + i) != 0) printf("*(div + %d) : %d\n", i, *(div + i)); } int *prime; prime = primes(a) + 1; for (i = 0; i < a; i++) { if (*(prime + i) != 0) printf("*(prime + %d) : %d\n", i, *(prime + i)); } </code></pre> <p>I get:</p> <pre><code>len = 6 len = 1 len = 2 len = 2 len = 3 len = 2 len = 4 len = 2 len = 4 len = 3 len = 4 len = 2 len = 6 *(prime + 1) : 2 *(prime + 2) : 3 *(prime + 3) : 4 *(prime + 4) : 5 *(prime + 5) : 6 *(prime + 6) : 7 *(prime + 10) : 11 *(prime + 11) : 12 </code></pre> <p>I can assure you that if I comment out all the traces except the ones for division() and call primes() I still get as a result:</p> <pre><code>*(div + 1) : 2 *(div + 2) : 3 *(div + 3) : 4 *(div + 5) : 6 *(div + 11) : 12 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 len = 0 *(prime + 1) : 2 *(prime + 2) : 3 *(prime + 3) : 4 *(prime + 5) : 6 *(prime + 11) : 12 </code></pre> <p>So, I know my code is bad; that's why I'm asking now (I'm still learning), I ask you:</p> <ul> <li>Why is it still returning the values of division() even though I have "freed" the memory of divResult?</li> <li>How can I get realloc() to work?</li> <li>Is there any easier way to do all this in <strong>separate</strong> functions?</li> </ul> <p>And last but not least: did anyone actually understand what I'm asking?</p>

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