Woo, it’s been a long time since I dealt with C pointers, but let me see if I can help. Coordinate_T *p; declares a pointer to a Coordinate_T struct. We don’t have any memory available yet, we just have a pointer to… nothing. p = (Coordinate_T *)malloc(sizeof(Coordinate_T)) actually allocates the memory for us. Now p … Read more
In the first code snippet you’re passing the value of the numbers variable. In the function you change a local variable, and doing so has no effect on the variable is the calling function. In the second snippet you correctly pass the address of numbers so it can be set in the function, and the … Read more
I’m just going to focus on what is causing your error (I didn’t read most of your code). Pointers are one of the concepts in C that take a long time to learn, and you have a long way to go. A pointer is just an address in memory, nothing else. You can think of … Read more
The errors in the code is: M == NULL is not a valid way to check if malloc is succeeded. You should use (*M) == NULL because the value is assigned to (*M), not M. The loop condition in ReservarMemoriaMatriz i<=m seems wrong. It should be i<=n. You forgot to free (*M)[n] in LiberarMemoriaMatriz. Corrected … Read more
As the man page for free will tell you, any argument except a pointer returned from malloc has undefined behaviour: The free() function frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc(). Otherwise, or if free(ptr) has already been called before, undefined behavior occurs. If ptr is NULL, no operation is … Read more
you shall not free() instances that have not been allocated through malloc(), though it’s unclear how the instance has been allocated before being given to that function, though it’s unlikely it’s been malloc()ed as this is C++, which leads me to 2. ; you should not free() C++ objects, but instead call delete that will … Read more
It is always a good habit to set the pointer to NULL after freeing it. Since the memory you are accessing is still intact you are seeing right values for l->val. Node *l=malloc(sizeof(Node)); l->key=”foo”; l->val=”bar”; free(l); l = NULL; solved free() not working correctly with struct