Basic network programming knowledge in C++

C, as a high-performance and efficient programming language, is also widely used in the field of network programming. This article will introduce basic network programming knowledge in C, including how to use the socket library for network programming, specific network communication processes, and some common network programming techniques.

1. Use the socket library for network programming

Socket is a network communication interface based on the TCP/IP protocol, which allows programs on different machines to communicate with each other. In C, you can use the socket library for network programming. The socket library provides a set of system calls and library functions that can easily establish network connections, send and receive data in programs.

When using the socket library for network programming, you first need to create a socket object. The method of creating a socket object is usually to call the socket() function, which accepts three parameters: address family, socket type and protocol type. For example:

#include <sys/socket.h>

int fd = socket(AF_INET, SOCK_STREAM, 0);

Among them, AF_INET means using the IPv4 address cluster, SOCK_STREAM means using the TCP protocol, and 0 means using the system default protocol.

Next, you need to connect the created socket object to the server. The way to connect to the server is usually to use the connect() function. For example:

#include <arpa/inet.h>

struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(SERVER_PORT);
inet_pton(AF_INET, SERVER_ADDR, &server_addr.sin_addr);

if (connect(fd, (const struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
    perror("connect error");
    exit(1);
}

Among them, SERVER_PORT and SERVER_ADDR are the port number and IP address of the server respectively. The function inet_pton() converts the IP address of string type into numeric type. If the connection fails, you can use the perror() function to output error information.

After the connection is successful, you can use the send() function and recv() function to send and receive data. For example:

char buf[BUFSIZ];
ssize_t n;
if ((n = recv(fd, buf, BUFSIZ, 0)) == -1) {
    perror("recv error");
    exit(1);
}

Among them, BUFSIZ represents the size of the buffer, and the function recv() represents receiving data from the socket object.

2. Specific network communication process

When using the socket library for network programming, common network communication processes include the connection between the client and the server, the sending and receiving of data, and the closing of the connection. . The specific process is as follows:

1. Create a socket object: use the socket() function to create a socket object, for example:

int fd = socket(AF_INET, SOCK_STREAM, 0);

2. Connect to the server: use the connect() function Connect to the server, for example:

struct sockaddr_in server_addr;
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(SERVER_PORT);
inet_pton(AF_INET, SERVER_ADDR, &server_addr.sin_addr);

if (connect(fd, (const struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
    perror("connect error");
    exit(1);
}

3. Send data: use the send() function to send data, for example:

char *data = "hello, world!";
if (send(fd, data, strlen(data), 0) == -1) {
    perror("send error");
    exit(1);
}

4. Receive data: use recv( ) function to receive data, for example:

char buf[BUFSIZ];
ssize_t n;
if ((n = recv(fd, buf, BUFSIZ, 0)) == -1) {
    perror("recv error");
    exit(1);
}

5. Close the connection: Use the close() function to close the socket object, for example:

close(fd);

3. Commonly used network programming Tips

When doing network programming, you need to pay attention to some common network programming skills to ensure the reliability and security of network communication.

1. Retransmission mechanism: Packet loss may occur during network communication. In order to ensure reliable transmission of data, a data retransmission mechanism can be used.
2. Timeout mechanism: When conducting network communication, a reasonable timeout should be set to avoid program blocking caused by too long waiting time.
3. Data encryption: Data involving user privacy should be encrypted and transmitted to prevent the data from being stolen and tampered with by criminals.
4. Code optimization: When performing network programming, code optimization should be performed to avoid the impact of redundant code on network communication.

In short, the knowledge of network programming in C is very important. Mastering this knowledge can help us easily communicate on the network and implement various network applications.

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