app2.cpp

#include <iostream>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/errno.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <string>
#include <unistd.h>
#include <thread>

using namespace std;

int main(int argc, char *argv[]) {
	constexpr int socket_family = 41;
	constexpr int socket_type = 2;
	constexpr int socket_protocol = 2;
	constexpr int maxlen = 60;

	int sock_id = socket(socket_family, socket_type, socket_protocol);
	if (sock_id < 0) return 0;

	char msg[maxlen+1];
	memset(msg, 0, sizeof(msg));
	int k = 0;
	while(k < 5) {
		int err = recv(sock_id, msg, maxlen, 0);
		if (err != -1) {
			cout << msg << '\n';
			++*msg;
			char c = *msg;
			if (!('a' <= c && c <= 'z'))
				*msg = 'a';
			send(sock_id, msg, strlen(msg) + 1, 0);
			k = 0;
		} else {
			++k;
			cout << "app2: err is -1, now k = " << k << endl;
		}
	}
	return 0;
}