Simple client in C

client.c

#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h> 

#define error(msg, ret) do { fprintf(stderr, "Error: " msg "\n"); exit(ret); } while (0)

int communicate(struct sockaddr_in * serv_addr, const char * message, char ** response) {
    int sockfd = 0, n = 0, len = 0;

    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
        error("could not create socket.", -1);

    if (connect(sockfd, (struct sockaddr *)serv_addr, sizeof(*serv_addr)) < 0) 
        error("connection failed.", -1);

    
    return 0;
}

struct sockaddr_in * init(int argc, char * argv[]) {
    struct sockaddr_in * serv_addr;
    char * ip, * port, * message;

    if (argc < 2) 
        error("use <program name> <server ip addr>:<port>", -1);

    serv_addr = calloc(1, sizeof(*serv_addr)); 

    ip = strtok(argv[1], ":");
    port = strtok(NULL, "");

    serv_addr->sin_family = AF_INET;
    serv_addr->sin_port = htons(atoi(port)); 

    if(inet_pton(AF_INET, ip, &serv_addr->sin_addr) <= 0)
        error("inet_pton error occured.", -1);

    return serv_addr;
}

int main(int argc, char *argv[])
{
    struct sockaddr_in * serv_addr;
    char * message;

    serv_addr = init(argc, argv);

    communicate(serv_addr, "message", &message);

    return 0;
}