• Interface declares operations, not data structure
• Implementation is hidden from client (encapsulation)
• Use features of programming language to ensure encapsulation

Common practice

• Allocation and deallocation of data structure handled by module
• Names of functions and variables begin with <modulename>_
• Provide as much generality/flexibility in interface as possible
• Use void pointers to allow polymorphism

#ifndef ARRAY_H

#define ARRAY_H

typedef struct Array *Array_T;

extern Array_T Array_new(void);

extern void Array_free(Array_T array);

extern void Array_insert(Array_T array, void *datap);

extern void Array_remove(Array_T array, void *datap);