Question

我一直在尝试修改http://beej.us/guide/bgnet/＆＃34; selectserver.c＆＃34;并允许用户定义的端口号并使用它代替

#define PORT "9034"   // port we're listening on

我试图让这项工作......

int PORT;
if (argc == 1)  {
    printf("\nNo argument passed. See example: ./selectserver 1234 \n\n");
    exit(-1);
} else {
    PORT = atoi(argv[1]);
    printf("PORT NO. : %d \n", PORT);
}

char* ptrPORT = (char *)&PORT;

...

这里是我修改过的代码：

/*
** selectserver.c -- a cheezy multiperson chat server
*/

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

//#define PORT "10000"   // port we're listening on

// 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 PORT;
    fd_set master;    // master file descriptor list
    fd_set read_fds;  // temp file descriptor list for select() 
    int fdmax;    // maximum file descriptor number
    int listener;     // listening socket descriptor
    int newfd;        // newly accept()ed socket descriptor
    struct sockaddr_storage remoteaddr; // client address
    socklen_t addrlen;
    char buf[256];    // buffer for client data
    int nbytes;

    char remoteIP[INET6_ADDRSTRLEN];

    int yes=1;        // for setsockopt() SO_REUSEADDR, below
    int i, j, rv;

    struct addrinfo hints, *ai, *p;

    FD_ZERO(&master);    // clear the master and temp sets
    FD_ZERO(&read_fds);

    // get us a socket and bind it
    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;

    if (argc == 1)  {
        printf("\nNo argument passed. See example: ./selectserver 1234 \n\n" );
        exit(-1);
    } else {
        PORT = atoi(argv[1]);
        printf("PORT NO. : %d \n", PORT);
    }

    char* ptrPORT = (char *)&PORT;

    if ((rv = getaddrinfo(NULL, ptrPORT, &hints, &ai)) != 0) {
            fprintf(stderr, "selectserver: %s\n", gai_strerror(rv));
            exit(1);
    }

    for(p = ai; p != NULL; p = p->ai_next) {
        listener = socket(p->ai_family, p->ai_socktype, p->ai_protocol);
        if (listener < 0) {
            continue;
        }

        // lose the pesky "address already in use" error message
        setsockopt(listener, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int));

        if (bind(listener, p->ai_addr, p->ai_addrlen) < 0) {
                close(listener);
            continue;
        }

        break;
    }

    // if we got here, it means we didn't get bound
    if (p == NULL) {
        fprintf(stderr, "selectserver: failed to bind\n");
        exit(2);
    }

    freeaddrinfo(ai); // all done with this

    // listen
    if (listen(listener, 10) == -1) {
        perror("listen");
        exit(3);
    }

    // add the listener to the master set
    FD_SET(listener, &master);

    // keep track of the biggest file descriptor
    fdmax = listener; // so far, it's this one

    // main loop
    for(;;) {
        read_fds = master; // copy it
        if (select(fdmax+1, &read_fds, NULL, NULL, NULL) == -1) {
            perror("select");
            exit(4);
        }

        // run through the existing connections looking for data to read
        for(i = 0; i <= fdmax; i++) {
            if (FD_ISSET(i, &read_fds)) { // we got one!!
                if (i == listener) {
                // handle new connections
                addrlen = sizeof remoteaddr;
                newfd = accept(listener,
                    (struct sockaddr *)&remoteaddr,
                    &addrlen);
                if (newfd == -1) {
                    perror("accept");
                } else {
                    FD_SET(newfd, &master); // add to master set
                    if (newfd > fdmax) {    // keep track of the max
                        fdmax = newfd;
                    }
                    printf("selectserver: new connection from %s on "
                        "socket %d\n",
                        inet_ntop(remoteaddr.ss_family,
                            get_in_addr((struct sockaddr*)&remoteaddr),
                            remoteIP, INET6_ADDRSTRLEN), newfd);
        }
            } else {
                // handle data from a client
                if ((nbytes = recv(i, buf, sizeof buf, 0)) <= 0) {
                    // got error or connection closed by client
                    if (nbytes == 0) {
                        // connection closed
                        printf("selectserver: socket %d hung up\n", i);
                    } else {
                        perror("recv");
                    }
                    close(i); // bye!
                    FD_CLR(i, &master); // remove from master set
                } else {
                    // we got some data from a client
                    for(j = 0; j <= fdmax; j++) {
                        // send to everyone!
                        if (FD_ISSET(j, &master)) {
                            // except the listener and ourselves
                            if (j != listener && j != i) {
                                if (send(j, buf, nbytes, 0) == -1) {
                                    perror("send");
                }
                }
            }
            }
        }

                } // END handle data from client
            } // END got new incoming connection
        } // END looping through file descriptors
    } // END for(;;)--and you thought it would never end!

    return 0;
}

它会顺利编译。现在我的问题是在执行时它会显示这个并且老实说我不知道如何修复它（我们昨天只进行了一次课堂讨论，所以我基本上对套接字编程没有看法）

./selectserver 10000

PORT NO. : 10000 
selectserver: nodename nor servname provided, or not known

请耐心等待我！

Answer 1

getaddrinfo将指向空终止字符串的指针作为第二个参数。

char* ptrPORT = (char *)&PORT;

上面的语句将指向int的指针类型转换为指向char的指针。这并没有改变它仍然指向int的事实。现在，如果仔细考虑，可以看到getaddrinfo将不知道如何正确读取您的值 - 它不是真正的空终止字符串。

但是，argv[1]是一个以空字符结尾的字符串，所以我的建议是按原样使用它而不是尝试转换它：

char* ptrPORT = argv[1];

Answer 2

service参数同时接受char *和int。但是，你真的想依靠char *和int之间的识别吗？在手册页enter link description here上，service参数可以是一个数字作为字符串。当hints.ai_flags设置为AI_NUMERICSERV。

时

用户定义的端口号

2 个答案: