Reverse a string in C/C++ using Client Server model

Last Updated : 26 Jan, 2018

This article describes a Client and Server setup where a Client connects, sends a string to server and the server shows the original string and sends reversed string to client using socket connection. Prerequisite : Socket Programming Examples:

Input : welcome
Output :emoclew

Input :geeks for geeks
Output :skeeg rof skeeg

Explanation In this, first setup client-server connection. When connection will setup, client will send user input string to server by send system call. At server side, server will wait for string sent by client. Server read string by read system call. After this, server will reverse the string and send back to client. Compiling : 1. First run the server program as

gcc Server.c -o server

2. Run the client program on another terminal

gcc Client.c -o client

3. Server program is waiting for string sent by client. 4. Input the string in client side. 5. Server program will print original string. 6. Client program will print reversed string.

Client.c

// C client code to send string to reverse
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 8090

// Driver code
int main()
{
    struct sockaddr_in address;
    int sock = 0, valread;
    struct sockaddr_in serv_addr;
    char str[100];

    printf("\nInput the string:");
    scanf("%[^\n]s", str);

    char buffer[1024] = { 0 };

    // Creating socket file descriptor
    if ((sock = socket(AF_INET,
                       SOCK_STREAM, 0))
        < 0) {
        printf("\n Socket creation error \n");
        return -1;
    }

    memset(&serv_addr, '0', sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);

    // Convert IPv4 and IPv6 addresses from
    // text to binary form 127.0.0.1 is local
    // host IP address, this address should be
    // your system local host IP address
    if (inet_pton(AF_INET, "127.0.0.1",
                  &serv_addr.sin_addr)
        <= 0) {
        printf("\nAddress not supported \n");
        return -1;
    }

    // connect the socket
    if (connect(sock, (struct sockaddr*)&serv_addr,
                sizeof(serv_addr))
        < 0) {
        printf("\nConnection Failed \n");
        return -1;
    }

    int l = strlen(str);

    // send string to server side
    send(sock, str, sizeof(str), 0);

    // read string sent by server
    valread = read(sock, str, l);

    printf("%s\n", str);

    return 0;
}

Server.c

// Server C code to reverse a
// string by sent from client
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 8090

// Driver code
int main()
{
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    char str[100];
    int addrlen = sizeof(address);
    char buffer[1024] = { 0 };
    char* hello = "Hello from server";

    // Creating socket file descriptor
    if ((server_fd = socket(AF_INET, 
                          SOCK_STREAM, 0)) == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Forcefully attaching socket to
    // the port 8090
    if (bind(server_fd, (struct sockaddr*)&address, 
                          sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // puts the server socket in passive mode
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }
    if ((new_socket = accept(server_fd,
                  (struct sockaddr*)&address,
                  (socklen_t*)&addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    // read string send by client
    valread = read(new_socket, str,
                   sizeof(str));
    int i, j, temp;
    int l = strlen(str);

    printf("\nString sent by client:%s\n", str);

    // loop to reverse the string
    for (i = 0, j = l - 1; i < j; i++, j--) {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }

    // send reversed string to client
    // by send system call
    send(new_socket, str, sizeof(str), 0);
    printf("\nModified string sent to client\n");

    return 0;
}