Socket Programming in C++ Cheatsheet

Overview

This README provides a comprehensive cheatsheet for socket programming in C++, covering key definitions, socket types, basic server-client code structure, system calls, and common debugging techniques. It is designed for students and professionals seeking a quick reference for socket programming concepts and coding patterns.

---

1. Socket Types

1.1 Stream Socket

• Protocol: TCP
• Use Case: Reliable, connection-oriented communication.

1.2 Datagram Socket

• Protocol: UDP
• Use Case: Connectionless, fast, but not reliable.

1.3 Raw Socket

• Protocol: IP Protocol
• Use Case: Direct access to lower network layers.

1.4 Server Socket

• Protocol: TCP/UDP
• Use Case: Listens for incoming client connections.

1.5 Client Socket

• Protocol: TCP/UDP
• Use Case: Connects to server to send/receive data.

---

2. Socket Programming Essentials

2.1 Header Files

Include the necessary header files for socket programming:

```cpp #include #include #include <sys/socket.h> #include <arpa/inet.h> #include <unistd.h> ```

2.2 Socket Creation

Create a socket using the socket() function:

```cpp int sockfd = socket(AF_INET, SOCK_STREAM, 0); ```

2.3 Bind Address to Socket

Bind an address to a socket with bind():

```cpp struct sockaddr_in server_addr; server_addr.sin_family = AF_INET; server_addr.sin_addr.s_addr = INADDR_ANY; server_addr.sin_port = htons(8080);

bind(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)); ```

2.4 Listen and Accept Connections

Set the socket to listen for connections and accept incoming connections:

```cpp listen(sockfd, 5); int client_socket = accept(sockfd, (struct sockaddr*)NULL, NULL); ```

2.5 Connect to Server (Client Side)

To connect to a server using a client socket:

```cpp struct sockaddr_in server_addr; server_addr.sin_family = AF_INET; server_addr.sin_port = htons(8080); inet_pton(AF_INET, "127.0.0.1", &server_addr.sin_addr);

connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr)); ```

---

3. System Calls Overview

3.1 Common System Calls

• socket(): Creates a socket and returns a file descriptor.
• bind(): Binds a socket to a specific IP address and port.
• listen(): Prepares a socket to accept incoming connections.
• accept(): Blocks the program until a connection is received.
• connect(): Connects a client to a remote server.
• send(): Sends data to a connected socket.
• recv(): Receives data from a connected socket.
• close(): Closes a socket.

3.2 Error Handling

Use perror() to print error messages:

```cpp if (sockfd < 0) { perror("Socket creation failed"); } ```

---

4. Basic Server Example

```cpp #include #include #include <sys/socket.h> #include <arpa/inet.h> #include <unistd.h>

int main() { int server_fd, new_socket; struct sockaddr_in address; int addrlen = sizeof(address);

server_fd = socket(AF_INET, SOCK_STREAM, 0);
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(8080);

bind(server_fd, (struct sockaddr*)&address, sizeof(address));
listen(server_fd, 3);

new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen);
char *message = "Hello from server";
send(new_socket, message, strlen(message), 0);
close(server_fd);
return 0;

} ```

---

5. Basic Client Example

```cpp #include #include #include <sys/socket.h> #include <arpa/inet.h> #include <unistd.h>

int main() { int sock = 0; struct sockaddr_in serv_addr; char buffer[1024] = {0};

sock = socket(AF_INET, SOCK_STREAM, 0);
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(8080);

inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr);
connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

send(sock, "Hello from client", strlen("Hello from client"), 0);
read(sock, buffer, 1024);
std::cout << buffer << std::endl;
close(sock);
return 0;

} ```

---

6. Debugging Techniques

6.1 Common Errors

• Address Already in Use: Occurs when binding to an already-used port.
• Connection Refused: The server may not be listening on the specified port.
• Broken Pipe: Happens when the server terminates unexpectedly.

6.2 Debugging Tips

• Use netstat -tulnp to check active ports.
• Use strace or gdb for in-depth debugging.