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PORemoving elements from dynamic arrays
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copied!<p>So, I have this:</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <string.h> void remove_element(int* array, int sizeOfArray, int indexToRemove) { int* temp = malloc((sizeOfArray - 1) * sizeof(int*)); // allocate an array with a size 1 less than the current one memcpy(temp, array, indexToRemove - 1); // copy everything BEFORE the index memcpy(temp+(indexToRemove * sizeof(int*)), temp+((indexToRemove+1) * sizeof(int*)), sizeOfArray - indexToRemove); // copy everything AFTER the index free (array); array = temp; } int main() { int howMany = 20; int* test = malloc(howMany * sizeof(int*)); for (int i = 0; i < howMany; ++i) (test[i]) = i; printf("%d\n", test[16]); remove_element(test, howMany, 16); --howMany; printf("%d\n", test[16]); return 0; } </code></pre> <p>It's reasonably self-explanatory, remove_element removes a given element of a dynamic array.</p> <p>As you can see, each element of test is initialised to an incrementing integer (that is, test[n] == n). However, the program outputs</p> <pre><code>16 16 </code></pre> <p>. Having removed an element of test, one would expect a call to to test[n] where n >= the removed element would result in what test[n+1] would have been before the removal. So I would expect the output</p> <pre><code>16 17 </code></pre> <p>. What's going wrong?</p> <p>EDIT: The problem has now been solved. Here's the fixed code (with crude debug printfs), should anyone else find it useful:</p> <pre><code>#include <stdio.h> #include <stdlib.h> #include <string.h> int remove_element(int** array, int sizeOfArray, int indexToRemove) { printf("Beginning processing. Array is currently: "); for (int i = 0; i < sizeOfArray; ++i) printf("%d ", (*array)[i]); printf("\n"); int* temp = malloc((sizeOfArray - 1) * sizeof(int)); // allocate an array with a size 1 less than the current one memmove( temp, *array, (indexToRemove+1)*sizeof(int)); // copy everything BEFORE the index memmove( temp+indexToRemove, (*array)+(indexToRemove+1), (sizeOfArray - indexToRemove)*sizeof(int)); // copy everything AFTER the index printf("Processing done. Array is currently: "); for (int i = 0; i < sizeOfArray - 1; ++i) printf("%d ", (temp)[i]); printf("\n"); free (*array); *array = temp; return 0; } int main() { int howMany = 20; int* test = malloc(howMany * sizeof(int*)); for (int i = 0; i < howMany; ++i) (test[i]) = i; printf("%d\n", test[16]); remove_element(&test, howMany, 14); --howMany; printf("%d\n", test[16]); return 0; } </code></pre>

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