Send Function in Linux C Programming

Introduction

The "send" function is a common function used in C programming on Linux systems to send data over a network connection. It is part of the BSD socket API and is used to transmit data from one socket to another. This function is widely used in network programming to establish communication between different processes or machines. In this article, we will explore the usage of the "send" function in Linux C programming and how it can be used to send data across network sockets.

Basic Syntax

The basic syntax of the "send" function in C programming is as follows:

#include <sys/types.h>
#include <sys/socket.h>
ssize_t send(int sockfd, const void *buf, size_t len, int flags);

Parameters

sockfd: The socket file descriptor that identifies the sending socket.

buf: Pointer to the buffer containing the data to be sent.

len: Size of the data in bytes.

flags: Optional flags to modify the behavior of the send operation.

Return Value

The "send" function returns the number of bytes sent on success, or -1 on failure. The actual number of bytes sent may be less than the requested length (len), so it is important to handle this possibility in your code.

Usage Example

Let's consider a simple example where we have a client-server architecture, and the client wants to send a message to the server using the "send" function. First, we need to create a socket and establish a connection between the client and server using the "connect" function:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#define PORT 8080
int main() {
    int sockfd;
    struct sockaddr_in server_addr;
    char *message = "Hello from client";
    // Create socket
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }
    // Configure server details
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    // Connect to the server
    if (connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
        perror("connection failed");
        exit(EXIT_FAILURE);
    }
    // Send data to the server
    if (send(sockfd, message, strlen(message), 0) == -1) {
        perror("send failed");
        exit(EXIT_FAILURE);
    }
    printf("Message sent to server successfully\n");
    close(sockfd);
    return 0;
}

Explanation

In the above example, we first create a TCP/IP socket using the "socket" function. Then, we configure the details of the server we want to connect to. In this case, we are using the local loopback address with a specific port number (8080). Next, we use the "connect" function to establish a connection to the server.

Finally, we use the "send" function to send the message "Hello from client" to the server. The "strlen" function is used to determine the length of the message. If the send operation is successful, the function will return the number of bytes sent, and we print a success message. Otherwise, an error message is printed.

Conclusion

The "send" function in Linux C programming is a crucial function for sending data over network sockets. It provides a simple and efficient way to transmit data between different processes or machines. Understanding the usage of this function is essential for network programming in the C language. In this article, we explored the basic syntax, parameters, return value, and demonstrated a usage example of the "send" function. By following these concepts, you can effectively use the "send" function to send data over network connections in your Linux C programs.