Имеем:

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

          #define BUFFSIZE 32
          void Die(char *mess) { perror(mess); exit(1); }

          int main(int argc, char *argv[]) {
            int sock;
            struct sockaddr_in echoserver;
            char buffer[BUFFSIZE];
            unsigned int echolen;
            int received = 0;
        char sentdstring[250];

            if (argc != 5) {
              fprintf(stderr, "USAGE: ./a.out <server_ip> <key> <ip> <proto>\n");
              exit(1);
            }
            /* Create the TCP socket */
            if ((sock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
              Die("Failed to create socket");
            }

/* Construct the server sockaddr_in structure */
            memset(&echoserver, 0, sizeof(echoserver));       /* Clear struct */
            echoserver.sin_family = AF_INET;                  /* Internet/IP */
            echoserver.sin_addr.s_addr = inet_addr(argv[1]);  /* IP address */
            echoserver.sin_port = htons(atoi("10000"));       /* server port */
            /* Establish connection */
            if (connect(sock,
                        (struct sockaddr *) &echoserver,
                        sizeof(echoserver)) < 0) {
              Die("Failed to connect with server");
            }

            
        /* Send the word to the server */

        //string sentdstring;
        //string sentdstring("key "+argv[2]+" intruder "+argv[3]+"  proto "+argv[4]);

            echolen = strlen(argv[2]);
            if (send(sock, argv[2], echolen, 0) != echolen) {
              Die("Mismatch in number of sent bytes");
            }

            echolen = strlen(argv[3]);
            if (send(sock, argv[3], echolen, 0) != echolen) {
              Die("Mismatch in number of sent bytes");
            }
        
            echolen = strlen(argv[4]);
            if (send(sock, argv[4], echolen, 0) != echolen) {
              Die("Mismatch in number of sent bytes");
            }
            /* Receive the word back from the server */
            fprintf(stdout, "Status: ");
            while (received < echolen) {
              int bytes = 0;
              if ((bytes = recv(sock, buffer, BUFFSIZE-1, 0)) < 1) {
                Die("Failed to receive bytes from server");
              }
              received += bytes;
              buffer[bytes] = '\0';        /* Assure null terminated string */
              fprintf(stdout, buffer);
            }
        
fprintf(stdout, "\n");
        close(sock);
           exit(0);
          }

вопрос... никак не могу понять (в силу того, что забыл) как мне всё запихнуть в одну переменную и отправить её, переменная sentdstring("key "+argv[2]+" intruder "+argv[3]+"  proto "+argv[4]);

Дальше бы просто

            echolen = strlen(sentdstring);
            if (send(sock, sentdstring, echolen, 0) != echolen) {
              Die("Mismatch in number of sent bytes");
            }

подскажите пожалуйста, а то чего то торможу...