Question

I am trying to implement a generic stack in c using void pointer to point to the data. the structure looks like this

struct record{
  void* data;
  struct record* previousRecord; 
};

where void pointer data is a pointer to the data a stack position will hold. If I implement a push function like this

struct record* push(struct record* tos, void* data){
  struct record* newtos = (struct record*)malloc(sizeof(struct record));
  newtos->data = data;
  newtos->previousRecord = tos;
  return newtos;
}

and push a couple of integer pointers and string pointers into the stack, is there any way I can print the values referenced by these pointers. My problem is that I have to specify the data type of value to print in the code if I use a printf function but the values stored in the stack can only be determined at run time

Answer 1

With address how would you know the type of data, it can be string or an integer address:

But you can keep an extra field in your record definition about type of value stored in data part, like below:

typedef enum { STRING, INT, CHAR} type;
struct record{
  type t;
  void* data;
  struct record* previousRecord; 
};

and write a common print function :

int print(struct record  *r){  

  switch(r->t){
     case CHAR:     return printf("%c", *((char*)(r->data)));
     case INT:      return printf("%d", *((int*)r->data));        
     case STRING:   return printf("%s", (char*)r->data);        
     default:       return printf("Error");
  }
} 

Here is a Project/A book that can be very helpful to write generic code in C.