fixing memory leak with destructors examples and documented it's unus…

…ual semantics

cvector.h

@@ -41,7 +41,17 @@
 #define cvector_clib_memmove memmove
 #endif
 
-typedef void (*cvector_elem_destructor_t)(void *elem);
+/* NOTE: Similar to C's qsort and bsearch, you will receive a T*
+ * for a vector of Ts. This means that you cannot use `free` directly
+ * as a destructor. Instead if you have for example a cvector_vector_type(int *)
+ * you will need to supply a function which casts `elem_ptr` to an `int**`
+ * and then does a free on what that pointer points to:
+ *
+ * ex:
+ *
+ * void free_int(void *p) { free(*(int **)p); }
+ */
+typedef void (*cvector_elem_destructor_t)(void *elem_ptr);
 
 typedef struct cvector_metadata_t {
     size_t size;
@@ -367,7 +377,7 @@ typedef struct cvector_metadata_t {
 
 /**
  * @brief cvector_set_elem_destructor - set the element destructor function
- * used to clean up removed elements
+ * used to clean up removed elements. The vector must NOT be NULL for this to do anything.
  * @param vec - the vector
  * @param elem_destructor_fn - function pointer of type cvector_elem_destructor_t used to destroy elements
  * @return void

test.c

@@ -12,13 +12,20 @@
 #include "cvector.h"
 #include "cvector_utils.h"
 
+static void free_string(void *str) {
+    if (str) {
+        free(*(char **)str);
+    }
+}
+
 int main() {
+
     cvector_vector_type(int) v           = NULL;
     cvector_vector_type(int) a           = NULL;
     cvector_vector_type(int) b           = NULL;
     cvector_vector_type(int) c           = NULL;
     cvector_vector_type(char *) str_vect = NULL;
-    cvector_set_elem_destructor(str_vect, free);
+    cvector_init(str_vect, 1, free_string);
 
     /* add some elements to the back */
     cvector_push_back(v, 10);

unit-tests.c

@@ -7,6 +7,18 @@
 #include <stdarg.h>
 #include <stdlib.h>
 
+static void free_string(void *ptr) {
+    if (ptr) {
+        free(*(char **)ptr);
+    }
+}
+
+static void free_int(void *ptr) {
+    if (ptr) {
+        free(*(int **)ptr);
+    }
+}
+
 UTEST(test, cvector_back) {
     cvector_vector_type(int) v = NULL;
     cvector_push_back(v, 0);
@@ -259,7 +271,7 @@ UTEST(test, vector_reserve) {
 UTEST(test, vector_free_all) {
     int i;
     cvector_vector_type(char *) v = NULL;
-    cvector_set_elem_destructor(v, free);
+    cvector_init(v, 1, free_string);
     for (i = 0; i < 10; ++i) {
         char *p = malloc(6);
         strcpy(p, "hello");
@@ -276,7 +288,7 @@ UTEST(test, vector_for_each_int) {
     cvector_iterator(int *) it;
     int i;
     cvector_vector_type(int *) v = NULL;
-    cvector_set_elem_destructor(v, free);
+    cvector_init(v, 1, free_int);
     for (i = 0; i < 10; ++i) {
         int *p = malloc(sizeof(int));
         *p     = 42;