Question

i have c function in my project which creates a struct and returns the pointer.

typedef struct object 
{
 float var1; 
 float var2; 
} 
Object; 

Object *createObject(float newVar1, float newVar2) 
{
 Object *object; //create new structure 
 object = (Object*)malloc(sizeof(Object)); //malloc size for struct object
 if(object != NULL) //is memory is malloc'd
 {
  object->var1 = newVar1; //set the data for var1
  object->var2 = newVar2; //set the data for var2
  return object; //return the pointer to the struct
 }
 return NULL; //if malloc fails, return NULL
}

now the struct gets used and after a while i want to delete this structure, i made this function:

void deleteMarnix(Object *objectPointer)
{
 free(objectPointer); //free the memory the pointer is pointing to
 objectPointer = NULL; //stop it from becomming a dangling pointer
}

this last code snippet shows how i make an object, use it and try to delete it, however, it seems that it doesn’t completely free the memory. what am i doing wrong?

Object *object = createObject(21.0f, 1.87f);
//do things here with object.
deleteMarnix(object);

Answer 1

What free() does is not free the memory held by the pointer completely, but actually makes it available for later use if we call a malloc after calling free().

An evidence to this is you will be able to access the memory location after calling free and before setting the pointer to NULL ( assuming you haven’t already called malloc() ). Of course the values will be reset to some default values. ( On some compilers i found int was set to 0 ).

Although there is no memory leak, this might answer your question.

Let us know 🙂