c语言 - 主机和客户端无法在我的聊天程序中使用 select() 进行通信

Question

我正在尝试编写一个简单的聊天程序，一个用户可以连接到主机。两人应该能够互相交谈（他们可能会互相打断，但这没关系）。我在select()方面遇到困难。这是代码：

客户端.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define MAXDATASIZE 1024 // max number of bytes we can get at once 
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*) sa)->sin_addr);
    }
    return &(((struct sockaddr_in6*) sa)->sin6_addr);
}
int main(int argc, char *argv[]) {
    int sockfd, numbytes;
    char buf[MAXDATASIZE];
    char buffer[1024];
    char *buff;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    char s[INET6_ADDRSTRLEN];
    char *port;
    int num;
    struct timeval tv;
    //select data
    fd_set rfds;
    fd_set wfds;
    FD_ZERO(&rfds);
    FD_ZERO(&wfds);

    if (argc != 2) {
        fprintf(stderr, "usage: client portn");
        exit(1);
    }
    port = argv[1];
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    if ((rv = getaddrinfo("localhost", port, &hints, &servinfo)) != 0) {
        fprintf(stderr, "getaddrinfo: %sn", gai_strerror(rv));
        return 1;
    }
    // loop through all the results and connect to the first we can
    for (p = servinfo; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("client: socket");
            continue;
        }
        if (connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("client: connect");
            continue;
        }
        break;
    }
    if (p == NULL) {
        fprintf(stderr, "client: failed to connectn");
        return 2;
    }
    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *) p->ai_addr),
            s, sizeof s);
    printf("client: connecting to %sn", s);
    freeaddrinfo(servinfo); // all done with this structure

    FD_SET(sockfd, &rfds);
    FD_SET(sockfd, &wfds);
    if (select(sockfd + 1, &rfds, &wfds, NULL, &tv) < 0) {
        perror("select");
        return -1;
    }
    if (FD_ISSET(sockfd, &wfds)) {
        while (1) {
            fgets(buffer, MAXDATASIZE - 1, stdin);
            if ((send(sockfd, buffer, strlen(buffer), 0)) == -1) {
                fprintf(stderr, "Failure Sending Messagen");
                close(sockfd);
                exit(1);
            } else {
                printf("Message being sent: %sn", buffer);
                break;
            }
        }
    }
    if (FD_ISSET(sockfd, &rfds)) {
        while (1) {
            if ((num = recv(sockfd, buffer, 10240, 0)) == -1) {
                //fprintf(stderr,"Error in receiving message!!n");
                perror("recv");
                exit(1);
            } else if (num == 0) {
                printf("Connection closedn");
                return 0;
            }
            //  num = recv(client_fd, buffer, sizeof(buffer),0);
            buffer[num] = '';
            printf("Message received: %sn", buffer);
            break;
        }
    }
    close(sockfd);
    return 0;
}

服务器.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <signal.h>
#define BACKLOG 10   // how many pending connections queue will hold
#define MAXDATASIZE 100 // max number of bytes we can get at once 
void sigchld_handler(int s) {
    while (waitpid(-1, NULL, WNOHANG) > 0);
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*) sa)->sin_addr);
    }
    return &(((struct sockaddr_in6*) sa)->sin6_addr);
}
int main(int argc, char *argv[]) {
    int sockfd; // set up socket
    int new_sockfd; //  new socket after connection
    struct addrinfo hints, *results, *p;
    struct sockaddr_storage their_addr; // connector's address information
    socklen_t sin_size;
    struct sigaction sa;
    int yes = 1;
    char s[INET6_ADDRSTRLEN];
    int rv;
    int i;
    struct timeval tv;
    int num;
    char buffer[10241];
    int nsock;
    char buf[MAXDATASIZE];
    int numbytes;
    char *port;
    //select data
    fd_set rfds;
    fd_set wfds;
    FD_ZERO(&rfds);
    FD_ZERO(&wfds);
    /* validate command-line arguments */
    if (argc != 2) {
        fprintf(stderr, "Usage: %s portn", argv[0]);
        exit(1);
    }
    tv.tv_sec = 100;
    tv.tv_usec = 0;
    /* only argument to port number (./sc [port])*/
    port = argv[1];
    bzero(&hints, sizeof (struct addrinfo));

    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE; // any IP
    if ((rv = getaddrinfo(NULL, port, &hints, &results)) != 0) {
        fprintf(stderr, "getaddrinfo: %sn", gai_strerror(rv));
        return 1;
    }
    // loop through all the results and bind to the first we can
    for (p = results; p != NULL; p = p->ai_next) {
        if ((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1) {
            perror("1: socket");
            continue;
        }
        if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes,
                sizeof (int)) == -1) {
            perror("setsockopt");
            exit(1);
        }
        if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
            close(sockfd);
            perror("server: bind");
            continue;
        }
        break;
    }
    if (p == NULL) {
        fprintf(stderr, "server: failed to bindn");
        return 2;
    }

    freeaddrinfo(results); // all done with this structure
    if (listen(sockfd, BACKLOG) == -1) {
        perror("listen");
        exit(1);
    }
    sa.sa_handler = sigchld_handler; // reap all dead processes
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;
    if (sigaction(SIGCHLD, &sa, NULL) == -1) {
        perror("sigaction");
        exit(1);
    }
    printf("server: waiting for connections...n");
    while (1) { // main accept() loop
        sin_size = sizeof their_addr;
        new_sockfd = accept(sockfd, (struct sockaddr *) &their_addr, &sin_size);
        if (new_sockfd == -1) {
            perror("accept");
            continue;
        }
        //get the clients info
        inet_ntop(their_addr.ss_family,
                get_in_addr((struct sockaddr *) &their_addr),
                s, sizeof s);
        printf("server: got connection from %sn", s);

        FD_SET(new_sockfd, &rfds);
        FD_SET(new_sockfd, &wfds);
        if (select(new_sockfd + 1, &rfds, &wfds, NULL, &tv) < 0) {
            perror("select");
            return -1;
        }
        if (FD_ISSET(new_sockfd, &rfds))
            while (1) {
                if ((num = recv(new_sockfd, buffer, 10240, 0)) == -1) {
                    //fprintf(stderr,"Error in receiving message!!n");
                    perror("recv");
                    exit(1);
                } else if (num == 0) {
                    printf("Connection closedn");
                    return 0;
                }
                //  num = recv(client_fd, buffer, sizeof(buffer),0);
                buffer[num] = '';
                printf("Message received: %sn", buffer);
                break;
            }

        if (FD_ISSET(new_sockfd, &wfds))
            while (1) {
                fgets(buffer, MAXDATASIZE - 1, stdin);
                if ((send(new_sockfd, buffer, strlen(buffer), 0)) == -1) {
                    fprintf(stderr, "Failure Sending Messagen");
                    close(new_sockfd);
                    exit(1);
                } else {
                    printf("Message being sent: %sn", buffer);
                    break;
                }
            }
    } //Outer While
    close(new_sockfd); // parent doesn't need this
    return 0;
}

主机和客户端无法通信。谁能告诉我问题出在哪里？

Answer 1

您需要在

循环内部调用select()，而不是在循环外部调用。 此外，每次调用 select() 时，您都必须重置fd_set和timeval结构。