C++ 入门
Linux 下的VSCode C++配置: https://www.cnblogs.com/zhumengke/articles/11629820.html
hello world
#include <iostream> using namespace std; int main() { cout << "Hello, world!" << endl; return 0; }
简单服务器
/** * a server * * linux 使用指南 * g++ -std=c++11 -g -o server main.cpp server.cpp * ./server */ //server.h #ifndef __SERVER_H__ #define __SERVER_H__ namespace ztf{ class Server{ public: Server(); ~Server(); public: void run(); }; } //namespace ztf #endif //server.cpp #include <iostream> #include <unistd.h> #include "server.h" namespace ztf{ Server::Server(){ std::cout << "Server construct..." << std::endl; } Server::~Server(){ std::cout << "Server destruct..." << std::endl; } void Server::run(){ while(true){ std::cout << "the server is running..." << std::endl; ::usleep(1000000); } } } //main.cpp #include <iostream> #include "server.h" int main(int argc,char* argv[]){ ztf::Server* server = new ztf::Server(); if(server){ server->run(); } return 0; }
linux 信号处理
// signal #include <iostream> #include <unistd.h> #include <signal.h> void sighandle(int sig) { std::cout << "sighup received :" << sig << std::endl; } int main(int argc,char **argv) { signal(SIGHUP, sighandle); signal(SIGINT, sighandle); signal(SIGQUIT, sighandle); // pause() causes the calling process (or thread) to sleep until a signal is delivered // that either terminates the process or causes the invocation of a signal-catching function. pause(); return 0; } //sigaction #include <iostream> #include <unistd.h> #include <signal.h> void sighandler(int sig){ std::cout << "received signal: " << sig << std::endl; } int main(int argc, char *argv[]) { struct sigaction act, oact; act.sa_handler = sighandler; sigfillset(&act.sa_mask); act.sa_flags = 0; sigaction(SIGINT, &act, &oact); pause(); return 0; }
UDP Server and UDP Client
// UDP server #include <sys/types.h> #include <sys/socket.h> #include <pthread.h> #include <netinet/in.h> #include <stdio.h> #include <string.h> #include <unistd.h> #include <stdlib.h> #include <arpa/inet.h> #include <iostream> #define SERVER_PORT 8000 int main(int argc, char *argv[]) { char buff_recv[512] = {0}; char buff_send[512] = "I am a server!"; int recv_num; int send_num; int sock_fd; int len; printf("Welcome! This is a UDP server.\n"); struct sockaddr_in serverAddr; struct sockaddr_in clientAddr; memset(&serverAddr, 0, sizeof(struct sockaddr_in)); //每个字节都用0填充 serverAddr.sin_family = AF_INET; //使用IPV4地址 serverAddr.sin_port = htons(SERVER_PORT); //端口 /* INADDR_ANY表示不管是哪个网卡接收到数据，只要目的端口是SERV_PORT，就会被该应用程序接收到 */ serverAddr.sin_addr.s_addr = htonl(INADDR_ANY); //自动获取IP地址 len = sizeof(serverAddr); sock_fd = socket(AF_INET, SOCK_DGRAM, 0); //sock_fd --- socket文件描述符 创建udp套接字 if (sock_fd < 0) { printf("socket error.\n"); exit(1); } int ret = bind(sock_fd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)); // 绑定socket if (ret < 0) { perror("bind error:"); exit(1); } while (true) { recv_num = recvfrom(sock_fd, buff_recv, sizeof(buff_recv), 0, (struct sockaddr *)&clientAddr, (socklen_t *)&len); if (recv_num < 0) { printf("recv error.\n"); break; } else { buff_recv[recv_num] = 0; printf("recv data from client:%s %u says: %s\n", inet_ntoa(clientAddr.sin_addr), ntohs(clientAddr.sin_port), buff_recv); send_num = sendto(sock_fd, buff_send, recv_num, 0, (struct sockaddr *)&clientAddr, sizeof(clientAddr)); if (send_num < 0) { printf("sendto error.\n"); break; } } } return 0; } // UDP Client #include <sys/types.h> #include <sys/socket.h> #include <pthread.h> #include <netinet/in.h> #include <stdio.h> #include <string.h> #include <unistd.h> #include <stdlib.h> #include <arpa/inet.h> #define SERVER_PORT 8000 #define SERVER_IP "127.0.0.1" int main(int argc, char **argv) { struct sockaddr_in addr; int sock; addr.sin_family = AF_INET; addr.sin_port = htons(SERVER_PORT); addr.sin_addr.s_addr = inet_addr(SERVER_IP); char buff_send[512] = "I am a client!"; char buff_recv[512] = {0}; int len = sizeof(addr); int n = 0; printf("This is a UDP client\n"); if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) < 0) { printf("socket error.\n"); exit(1); } if (addr.sin_addr.s_addr == INADDR_NONE) { printf("Incorrect ip address!"); close(sock); exit(1); } n = sendto(sock, buff_send, strlen(buff_send), 0, (struct sockaddr *)&addr, sizeof(addr)); if (n < 0) { printf("sendto error.\n"); close(sock); } n = recvfrom(sock, buff_recv, 512, 0, (struct sockaddr *)&addr, (socklen_t *)&len); if (n > 0) { buff_recv[n] = 0; printf("received from sever:"); puts(buff_recv); } else if (n == 0) printf("server closed.\n"); else if (n == -1) printf("recvfrom error.\n"); close(sock); return 0; }
TCP Server and TCP Client
//tcp Server #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 8444 #define MESSAGE_SIZE 1024 int main() { int ret = -1; int socket_fd = -1; int accept_fd = -1; int curpos = 0; int backlog = 10; int flag = 1; char recvBuf[MESSAGE_SIZE] = {0}; char sendBuf[MESSAGE_SIZE] = {0}; struct sockaddr_in local_addr, remote_addr; //create a tcp socket socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) { perror("create socket error"); exit(1); } //set option of socket ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag)); if (ret == -1) { perror("setsockopt error"); } //set local address local_addr.sin_family = AF_INET; local_addr.sin_port = htons(PORT); local_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(local_addr.sin_zero), 8); //bind socket ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr_in)); if (ret == -1) { perror("bind error"); exit(1); } ret = listen(socket_fd, backlog); if (ret == -1) { perror("listen error"); exit(1); } //loop for (;;) { int addr_len = sizeof(struct sockaddr_in); //accept an new connection accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, (socklen_t *)&addr_len); for (;;) { memset(recvBuf, 0, sizeof(recvBuf)); //receive network data and print it ret = recv(accept_fd, recvBuf, sizeof(recvBuf), 0); if (ret == 0) { break; } printf("receive message:%s\n", recvBuf); send(accept_fd, recvBuf, sizeof(recvBuf), 0); } printf("close client connection...\n"); close(accept_fd); } printf("quit server...\n"); close(socket_fd); return 0; } // tcp client #include <stdio.h> #include <string.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <errno.h> #include <netdb.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <iostream> #define SERVER_IP "127.0.0.1" #define SERVER_PORT 8444 #define MESSAGE_LENGTH 1024 int main() { int ret = -1; int socket_fd; //server addr struct sockaddr_in serverAddr; char sendbuf[MESSAGE_LENGTH]; char recvbuf[MESSAGE_LENGTH]; int data_len; if ((socket_fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) { perror("socket"); return 1; } serverAddr.sin_family = AF_INET; serverAddr.sin_port = htons(SERVER_PORT); serverAddr.sin_addr.s_addr = inet_addr(SERVER_IP);//inet_addr()函数，将点分十进制IP转换成网络字节序IP if (connect(socket_fd, (struct sockaddr *)&serverAddr, sizeof(serverAddr)) < 0) { perror("connect"); return 1; } printf("success to connect server...\n"); while (1) { memset(sendbuf, 0, MESSAGE_LENGTH); printf("<<<<send message:"); std::cin >> sendbuf; ret = send(socket_fd, sendbuf, strlen(sendbuf), 0); if (ret <= 0) { printf("the connection is disconnection!\n"); break; } if (strcmp(sendbuf, "quit") == 0) { break; } printf(">>> echo message:"); recvbuf[0] = '\0'; data_len = recv(socket_fd, recvbuf, MESSAGE_LENGTH, 0); recvbuf[data_len] = '\0'; printf("%s\n", recvbuf); } close(socket_fd); return 0; }
wait and waitpid
#include <stdio.h> #include <iostream> #include <unistd.h> #include <sys/wait.h> /** * fork: * On success, the PID of the child process is returned in the parent, and 0 is returned in the child. * On failure, -1 is returned in the parent, no child process is created, */ int main(int argc, char *argv[]) { pid_t pid = -1; for (int i = 0; i < 4; i++) { std::cout << i << std::endl; sleep(2); if (pid != 0) { pid = fork(); } } if (pid == 0) //子进程 { sleep(2); } else //主进程 { /** * waitpid: * pid=-1时，等待任何一个子进程退出，没有任何限制，此时waitpid和wait的作用一模一样。 * status用来保存被收集进程退出时的一些状态, NULL不需要收集进程退出的状态 * options提供了一些额外的选项来控制waitpid */ while ((pid = waitpid(-1, NULL, 0)) != -1) { printf("the pid=%d is dead!\n", pid); } } }
多进程 + fork
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 8111 #define MESSAGE_SIZE 1024 int main() { int ret = -1; int pid; int socket_fd = -1; int accept_fd = -1; int curpos = 0; int backlog = 10; int flag = 1; struct sockaddr_in local_addr, remote_addr; //create a tcp socket socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) { perror("create socket error"); exit(1); } //set option of socket ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &flag, sizeof(flag)); if (ret == -1) { perror("setsockopt error"); } //set local address local_addr.sin_family = AF_INET; local_addr.sin_port = htons(PORT); local_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(local_addr.sin_zero), 8); //bind socket ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr_in)); if (ret == -1) { perror("bind error"); exit(1); } ret = listen(socket_fd, backlog); if (ret == -1) { perror("listen error"); exit(1); } for (;;) { int addr_len = sizeof(struct sockaddr_in); //accept an new connection, block...... accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, (socklen_t *)&addr_len); //create a sub process pid = fork(); //子进程 if (pid == 0) { char in_buf[MESSAGE_SIZE] = {0}; for (;;) { memset(in_buf, 0, MESSAGE_SIZE); ret = recv(accept_fd, &in_buf, MESSAGE_SIZE, 0); if (ret == 0) { break; } printf("receive message:%s\n", in_buf); send(accept_fd, (void *)in_buf, MESSAGE_SIZE, 0); } printf("close client connection...\n"); close(accept_fd); } //parent process } if (pid != 0) //主进程 { printf("quit server...\n"); close(socket_fd); } return 0; }
select
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 8888 #define FD_SIZE 1024 #define MESSAGE_SIZE 1024 int main() { int ret = -1; int pid; int accept_fd = -1; int socket_fd = -1; int accept_fds[FD_SIZE] = {-1,}; int curpos = -1; int maxpos = 0; int backlog = 10; int flags = 1; //open REUSEADDR option int max_fd = -1; fd_set fd_sets; int events = 0; struct sockaddr_in local_addr, remote_addr; //create a tcp socket socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) { perror("create socket error"); exit(1); } //set option of socket ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &flags, sizeof(flags)); if (ret == -1) { perror("setsockopt error"); } //NONBLOCK flags = fcntl(socket_fd, F_GETFL, 0); fcntl(socket_fd, F_SETFL, flags | O_NONBLOCK); //set local address local_addr.sin_family = AF_INET; local_addr.sin_port = htons(PORT); local_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(local_addr.sin_zero), 8); //bind socket ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr_in)); if (ret == -1) { perror("bind error"); exit(1); } ret = listen(socket_fd, backlog); if (ret == -1) { perror("listen error"); exit(1); } max_fd = socket_fd; //每次都重新设置 max_fd for (int i = 0; i < FD_SIZE; i++) { accept_fds[i] = -1; } for (;;) { FD_ZERO(&fd_sets); //清空sets FD_SET(socket_fd, &fd_sets); //将socket_fd 添加到sets for (int k = 0; k < maxpos; k++) { if (accept_fds[k] != -1) { if (accept_fds[k] > max_fd) { max_fd = accept_fds[k]; } printf("fd:%d, k:%d, max_fd:%d\n", accept_fds[k], k, max_fd); FD_SET(accept_fds[k], &fd_sets); //继续向sets添加fd } } //遍历所有的fd events = select(max_fd + 1, &fd_sets, NULL, NULL, NULL); if (events < 0) { perror("select"); break; } else if (events == 0) { printf("select time out ......"); continue; } else if (events) { printf("events:%d\n", events); if (FD_ISSET(socket_fd, &fd_sets)) { // 如果来的是新连接 printf("listen event :1\n"); int a = 0; for (; a < FD_SIZE; a++) { if (accept_fds[a] == -1) { curpos = a; break; } } if (a == FD_SIZE) { printf("the connection is full!\n"); continue; } int addr_len = sizeof(struct sockaddr_in); accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, (socklen_t *)&addr_len); //创建一个新连接的fd int flags = fcntl(accept_fd, F_GETFL, 0); //取出新连接的 fd 的相关选项 fcntl(accept_fd, F_SETFL, flags | O_NONBLOCK); //设置为非阻塞 accept_fds[curpos] = accept_fd; if (curpos + 1 > maxpos) { maxpos = curpos + 1; } if (accept_fd > max_fd) { max_fd = accept_fd; } printf("new connection fd:%d, curpos = %d \n", accept_fd, curpos); } for (int j = 0; j < maxpos; j++) { if ((accept_fds[j] != -1) && FD_ISSET(accept_fds[j], &fd_sets)) { //有事件时 printf("accept event :%d, accept_fd: %d\n", j, accept_fds[j]); char in_buf[MESSAGE_SIZE]; memset(in_buf, 0, MESSAGE_SIZE); int ret = recv(accept_fds[j], &in_buf, MESSAGE_SIZE, 0); if (ret == 0) { close(accept_fds[j]); accept_fds[j] = -1; } printf("receive message:%s\n", in_buf); send(accept_fds[j], (void *)in_buf, MESSAGE_SIZE, 0); } } } } printf("quit server...\n"); close(socket_fd); return 0; }
epoll
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <errno.h> #include <sys/epoll.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 8888 #define FD_SIZE 20 #define MAX_EVENTS 20 #define TIME_OUT 500 #define MESSAGE_SIZE 1024 int main() { int ret = -1; int socket_fd = -1; int accept_fd = -1; int flags = 1; int backlog = 10; struct sockaddr_in local_addr, remote_addr; struct epoll_event ev, events[FD_SIZE]; int epoll_fd = -1; int event_number = 0; //creat a tcp socket socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) { perror("create socket error"); exit(1); } //set REUSERADDR ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, (char *)&flags, sizeof(flags)); if (ret == -1) { perror("setsockopt error"); } //set NONBLOCK flags = fcntl(socket_fd, F_GETFL, 0); fcntl(socket_fd, F_SETFL, flags | O_NONBLOCK); //set address local_addr.sin_family = AF_INET; local_addr.sin_port = htons(PORT); local_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(local_addr.sin_zero), 8); //bind addr ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr_in)); if (ret == -1) { perror("bind error"); exit(1); } if (listen(socket_fd, backlog) == -1) { perror("listen error"); exit(1); } //create epoll epoll_fd = epoll_create(256); //the size argument is ignored ev.data.fd = socket_fd; ev.events = EPOLLIN; epoll_ctl(epoll_fd, EPOLL_CTL_ADD, socket_fd, &ev); //将socket_fd 添加到epoll中 for (;;) { //events 表示一共有多少事件被侦听 //MAX_EVENTS 表示在events个事件中，本次调用最多能返回多少个被解发的事件 //TIME_OUT 表示本次调用最多等多长时间 //event_number 表示本次调用真正有多少事件被解发 event_number = epoll_wait(epoll_fd, events, MAX_EVENTS, TIME_OUT); for (int i = 0; i < event_number; i++) { if (events[i].data.fd == socket_fd) { // 如果是侦听端口的事件 printf("listen event... \n"); int addr_len = sizeof(struct sockaddr_in); accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, (socklen_t *)&addr_len); //将新创建的socket设置为 NONBLOCK 模式 flags = fcntl(accept_fd, F_GETFL, 0); fcntl(accept_fd, F_SETFL, flags | O_NONBLOCK); ev.data.fd = accept_fd; ev.events = EPOLLIN | EPOLLET; epoll_ctl(epoll_fd, EPOLL_CTL_ADD, accept_fd, &ev); printf("new accept fd:%d\n", accept_fd); } else if (events[i].events & EPOLLIN) { //printf("accept event :%d\n",i); char in_buf[MESSAGE_SIZE]; memset(in_buf, 0, MESSAGE_SIZE); //receive data ret = recv(events[i].data.fd, &in_buf, MESSAGE_SIZE, 0); if (ret == MESSAGE_SIZE) { printf("maybe have data...."); } if (ret <= 0) { switch (errno) { case EAGAIN: //说明暂时已经没有数据了，要等通知 break; case EINTR: //被终断了，再来一次 printf("recv EINTR... \n"); ret = recv(events[i].data.fd, &in_buf, MESSAGE_SIZE, 0); break; default: printf("the client is closed, fd:%d\n", events[i].data.fd); epoll_ctl(epoll_fd, EPOLL_CTL_DEL, events[i].data.fd, &ev); close(events[i].data.fd); ; } } printf(">>>receive message:%s\n", in_buf); send(events[i].data.fd, &in_buf, ret, 0); } } } return 0; }
reinterpret_const
#include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <errno.h> #include <sys/epoll.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #define PORT 8888 #define FD_SIZE 20 #define MAX_EVENTS 20 #define TIME_OUT 500 #define MESSAGE_SIZE 1024 int main() { int ret = -1; int socket_fd = -1; int accept_fd = -1; int flags = 1; int backlog = 10; struct sockaddr_in local_addr, remote_addr; struct epoll_event ev, events[FD_SIZE]; int epoll_fd = -1; int event_number = 0; //creat a tcp socket socket_fd = socket(AF_INET, SOCK_STREAM, 0); if (socket_fd == -1) { perror("create socket error"); exit(1); } //set REUSERADDR ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, (char *)&flags, sizeof(flags)); if (ret == -1) { perror("setsockopt error"); } //set NONBLOCK flags = fcntl(socket_fd, F_GETFL, 0); fcntl(socket_fd, F_SETFL, flags | O_NONBLOCK); //set address local_addr.sin_family = AF_INET; local_addr.sin_port = htons(PORT); local_addr.sin_addr.s_addr = INADDR_ANY; bzero(&(local_addr.sin_zero), 8); //bind addr ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr_in)); if (ret == -1) { perror("bind error"); exit(1); } if (listen(socket_fd, backlog) == -1) { perror("listen error"); exit(1); } //create epoll epoll_fd = epoll_create(256); //the size argument is ignored ev.data.fd = socket_fd; ev.events = EPOLLIN; epoll_ctl(epoll_fd, EPOLL_CTL_ADD, socket_fd, &ev); //将socket_fd 添加到epoll中 for (;;) { //events 表示一共有多少事件被侦听 //MAX_EVENTS 表示在events个事件中，本次调用最多能返回多少个被解发的事件 //TIME_OUT 表示本次调用最多等多长时间 //event_number 表示本次调用真正有多少事件被解发 event_number = epoll_wait(epoll_fd, events, MAX_EVENTS, TIME_OUT); for (int i = 0; i < event_number; i++) { if (events[i].data.fd == socket_fd) { // 如果是侦听端口的事件 printf("listen event... \n"); int addr_len = sizeof(struct sockaddr_in); accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, (socklen_t *)&addr_len); //将新创建的socket设置为 NONBLOCK 模式 flags = fcntl(accept_fd, F_GETFL, 0); fcntl(accept_fd, F_SETFL, flags | O_NONBLOCK); ev.data.fd = accept_fd; ev.events = EPOLLIN | EPOLLET; epoll_ctl(epoll_fd, EPOLL_CTL_ADD, accept_fd, &ev); printf("new accept fd:%d\n", accept_fd); } else if (events[i].events & EPOLLIN) { //printf("accept event :%d\n",i); char in_buf[MESSAGE_SIZE]; memset(in_buf, 0, MESSAGE_SIZE); //receive data ret = recv(events[i].data.fd, &in_buf, MESSAGE_SIZE, 0); if (ret == MESSAGE_SIZE) { printf("maybe have data...."); } if (ret <= 0) { switch (errno) { case EAGAIN: //说明暂时已经没有数据了，要等通知 break; case EINTR: //被终断了，再来一次 printf("recv EINTR... \n"); ret = recv(events[i].data.fd, &in_buf, MESSAGE_SIZE, 0); break; default: printf("the client is closed, fd:%d\n", events[i].data.fd); epoll_ctl(epoll_fd, EPOLL_CTL_DEL, events[i].data.fd, &ev); close(events[i].data.fd); ; } } printf(">>>receive message:%s\n", in_buf); send(events[i].data.fd, &in_buf, ret, 0); } } } return 0; }
static_cast
#include <iostream> class Base { public: int a; int b; }; class Derived : public Base { public: int c; int d; }; int main(int argc, char *argv[]) { Base *b = new Base(); Derived *d = new Derived(); Base *p = static_cast<Base *>(d); p->a = 1; p->b = 2; std::cout << "Base: " << p->a << ", " << p->b << std::endl; Derived *dp = static_cast<Derived *>(b); dp->a = 4; dp->b = 5; dp->c = 6; dp->d = 666; std::cout << "Derived: " << dp->a << ", " << dp->b << ", " << dp->c << ", " << dp->d << std::endl; return 0; }
dynamic_cast
#include <iostream> class Base { public: Base(int a, int b){ this->a = a; this->b = b; } public: virtual void print(){ std::cout << "member: a=" << a << ", b=" << b << std::endl; } public: int a; int b; }; class Derived1: public Base { public: Derived1(int a, int b, int o):Base(a, b){ c = o; } public: virtual void print(){ std::cout << "member: a=" << a << ", b=" << b << ", c=" << c << std::endl; } public: int c; }; class Derived2: public Base { public: Derived2(int a, int b, int o):Base(a, b){ d = o; } public: virtual void print() { std::cout << "member: a=" << a << ", b=" << b << ", d=" << d << std::endl; } public: int d; }; int main(int argc, char* argv[]) { Base *b = new Base(1, 2); b = dynamic_cast<Base*>(new Derived1(3, 4, 5)); b->print(); b = static_cast<Base*>(new Derived2(6, 7, 8)); b->print(); }
const_cast
#include <iostream> class Base { public: Base(int a, int b){ this->a = a; this->b = b; } public: int a; int b; }; int main(int argc, char* argv[]) { const Base *b = new Base(1, 2); std::cout<< "Base: a=" << b->a << ", b=" << b->b << std::endl; //b->a = 4; 报错 //b->b = 5; 报错 Base *pb = const_cast<Base*>(b); pb->a = 3; pb->b = 4; std::cout<< "Base: a=" << pb->a << ", b=" << pb->b << std::endl; return 0; }
const_point
#include <stdio.h> int main(int argc, char* argv[]) { int p = 3; int a = 4; const int pp = 4; const int *point = &pp; int const *p2 = &pp; int* const p3 = &p; const int* const p4 = &p; int const * const p5 = &p; printf("p = %d \n", p); ////////////////////////// printf("pp = %d \n", pp); //pp = 5; //报错 ////////////////////////// printf("*point = %d \n", *point); //*point = 7; //报错 point = &p; printf("*point = %d \n", *point); ////////////////////////// printf("*p2 = %d \n", *p2); //*p2 = 8; //报错 p2 = &p; printf("*p2 = %d \n", *p2); ////////////////////////// printf("*p3 = %d \n", *p3); *p3 = 9; printf("*p3 = %d \n", *p3); //p3 = &a; //报错 ////////////////////////// printf("*p4 = %d \n", *p4); //*p4 = 9; //报错 //p4 = &a; //报错 // ////////////////////////// printf("*p5 = %d \n", *p5); //*p5 = 9; //报错 //p5 = &a; //报错 }
vs2017 添加lib和头文件
如果我们借鉴别人写好的代码，放进vs2010编译器时常常出现这样的报错，无法打开源文件 “stdafx.h”：
这是因为在低版本的编译器中，需要添加这部分，比如vc6.0到vs2008，而在vs2010以上版本的编译器中如果出现了这种报错，就查看一下属性->c/c++->预编译头->预编译头文件，其中是否包含了”stdafx.h”文件，如果有注释掉上述代码就好，不会对程序造成影响。
VS2017添加lib库及其头文件
A、添加工程的头文件目录：工程---属性---配置属性---c/c++---常规---附加包含目录：加上头文件存放目录。
B、添加文件引用的lib静态库路径：工程---属性---配置属性---链接器---常规---附加库目录：加上lib文件存放目录。
C 然后添加工程引用的lib文件名：工程---属性---配置属性---链接器---输入---附加依赖项：加上lib文件名
创建类对象
栈中创建： Human human; // 会自动调用析构函数
堆中创建：Human* p = new Human(); // 不会自动调用析构函数，需要显示的调用delete方法，否则会造成内存泄漏
