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Basic knowledge, features and object-oriented details of C language
Basic Knowledge
Structure
In addition to providing basic data types, C also allows users to define their own custom data types through structures. A structure is a way to group together different data types under a single name, making it easier to represent real-world entities. Structures are considered the precursor to classes in object-oriented programming languages. For example:
typedef struct {
float x;
float y;
} Point;
This defines a point in a 2D coordinate system with two members: x and y. The members of a structure are called its fields or members. These can be simple data types, other structures, or even nested structures. An example of a linked list can be defined as follows:
typedef struct node {
void *data; // Pointer to data
int dataLength; // Length of data
struct node *next; // Pointer to the next node
} Node;
As you can see, the 'next' pointer within the 'node' structure points to another 'node' type, allowing for the creation of a chain of nodes.
Function Pointers
Pointers are one of the most powerful features of the C language, giving it more flexibility compared to other programming languages. Learning C requires a solid understanding of pointers. A function pointer is essentially a pointer that points to the memory address of a function. This allows functions to be passed as arguments to other functions, enabling asynchronous operations and more dynamic code execution.
For example, the signal registration function in UNIX/Linux has the following prototype:
void (*signal(int signo, void (*func)(int)))(int);
To use this, you need to define a signal handler externally and then register it using signal(sigNo, handler). When the signal is triggered, the process will call back the registered handler.
Using Function Pointers as Structure Members
As mentioned earlier, structure members can be simple data types, other structures, or even pointers. When a function pointer is used as a member of a structure, it enables the structure to perform specific operations on its data. This creates an entity that contains both data and the functions that manipulate it, which is a key concept in object-oriented programming.
Object-Oriented Language Features
In general, inheritance, encapsulation, and polymorphism are considered the three core features of an object-oriented language. These features allow for better abstraction and modularity compared to procedural programming. Although object-oriented thinking is often associated with specific programming languages, it is actually a software design philosophy that can be applied independently of the language used.
Despite this, object-oriented languages tend to produce more readable and intuitive code that aligns better with human thought processes. While C is not inherently object-oriented, it provides the necessary tools to implement object-oriented principles effectively.
Object-Oriented Design in C
Although C is not a purely object-oriented language, it is possible to design code that mimics object-oriented behavior using structures and function pointers. In this section, I'll demonstrate how to create an object-oriented style linked list in C.
Defining an Interface
An interface is a crucial concept in object-oriented programming. It defines the set of functions that an object can expose without revealing the internal implementation details. This separation makes it easier to modify the implementation without affecting the code that uses the interface.
For example, here's an interface definition for a linked list:
#ifndef _ILIST_H
#define _ILIST_H
// Define the node structure
typedef struct node {
void *data;
struct node *next;
} Node;
// Define the linked list structure
typedef struct list {
struct list *_this;
Node *head;
int size;
void (*insert)(void *node);
void (*drop)(void *node);
void (*clear)();
int (*getSize)();
void* (*get)(int index);
void (*print)();
} List;
// Function declarations
void insert(void *node);
void drop(void *node);
void clear();
int getSize();
void* get(int index);
void print();
#endif /* _ILIST_H */
This interface allows for operations such as inserting, removing, clearing, retrieving the size, getting an element by index, and printing the list.
Interface Implementation
Now, let's look at the implementation of the linked list interface:
List *ListConstruction() {
List *list = (List*)malloc(sizeof(List));
Node *node = (Node*)malloc(sizeof(Node));
list->head = node;
list->insert = insert;
list->drop = drop;
list->clear = clear;
list->size = 0;
list->getSize = getSize;
list->get = get;
list->print = print;
list->_this = list;
return list;
}
The _this pointer ensures that external calls to the list methods are correctly mapped to the actual instance, simplifying the code.
Testing the Implementation
Finally, let's test the linked list implementation:
int main(int argc, char** argv) {
List *list = (List*)ListConstruction();
list->insert("Apple");
list->insert("Borland");
list->insert("Cisco");
list->insert("Dell");
list->insert("Electrolux");
list->insert("FireFox");
list->insert("Google");
list->print();
printf("list size = %d", list->getSize());
Node node;
node.data = "Electrolux";
node.next = NULL;
list->drop(&node);
node.data = "Cisco";
node.next = NULL;
list->drop(&node);
list->print();
printf("list size = %d", list->getSize());
list->clear();
return 0;
}
This test demonstrates the functionality of the linked list, including insertion, deletion, and retrieval of elements.
Conclusion
C was born on the UNIX platform, which emphasizes a design philosophy of simplicity and modularity. C is a powerful yet simple language that allows developers to build complex applications from small, reusable components. While C is not inherently object-oriented, it provides the necessary mechanisms to implement object-oriented concepts. The illusion that C is a procedural language stems from its early development when object-oriented thinking was still evolving. In reality, C offers the flexibility and power to create a wide range of applications, depending on the developer's needs.