c - 如何将程序中定义的默认端口号添加到 getaddrinfo()

Question

我想在我的 header 中定义一个端口号(例如 #define port 9191 )并使用它来调用 getaddrinfo() 。但我收到错误，因为参数服务是 char const* 。如何使用#define d 调用 getaddrinfo() 时的端口号？

下面我#define d 端口为 9191并尝试将其转换为 char*使用sprintf() 。然后我尝试在调用getaddrinfo()时使用它:

#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>

#define PORT 9191 // here the define port number
#define LEN 500

int
main(int argc, char *argv[])
{
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    struct sockaddr_in cliAddr;  // the from address of a client
    int sock, s, clilen;
    char *service; // declared variable name
    struct sockaddr_in storage;

    ssize_t n;
    char receive[LEN], message[LEN];
    sprintf(service, "%d", PORT); // i have tried convert it to char

    if (argc != 1) {
        fprintf(stderr, "Usage: %s \n", argv[0]);
        exit(EXIT_FAILURE);
    }

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_INET;    /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
    hints.ai_flags = 0;    /* For wildcard IP address */
    hints.ai_protocol = 0;          /* Any protocol */
    hints.ai_canonname = NULL;
    hints.ai_addr = NULL;
    hints.ai_next = NULL;

    s = getaddrinfo(NULL, &service, &hints, &result);
    if (s != 0) {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
        exit(EXIT_FAILURE);
    }

    /* getaddrinfo() returns a list of address structures.
       Try each address until we successfully bind(2).
       If socket(2) (or bind(2)) fails, we (close the socket
       and) try the next address. */

    for (rp = result; rp != NULL; rp = rp->ai_next) {
        sock = socket(rp->ai_family, rp->ai_socktype,
            rp->ai_protocol);
        if (sock == -1)
            continue;

        if (bind(sock, rp->ai_addr, rp->ai_addrlen) == 0)
            break;                  /* Success */

        close(sock);
    }

    if (rp == NULL) {               /* No address succeeded */
        fprintf(stderr, "Could not bind\n");
        exit(EXIT_FAILURE);
    }

    freeaddrinfo(result);           /* No longer needed */

    /* Read datagrams and echo them back to sender */

    while (1)
    {
        //bzero(receive, LEN);
        clilen = sizeof(cliAddr);
        n = recvfrom(sock, receive, strlen(receive), 0, (struct sockaddr*)&cliAddr, &clilen);
        if (n < 0)
        {
            fprintf(stderr, "error in reading\n");
            exit(EXIT_FAILURE);
        }
        printf("The client message: %s\n ", receive);
        bzero(message, LEN);

        fgets(message, sizeof(message), stdin);

        message[LEN] = '\0';
        printf("%s\n", message);
        n = sendto(sock, message, strlen(message), 0, (struct sockaddr*)&cliAddr, sizeof(cliAddr));
        printf("%ld\n", n);
        if (n < 0)
        {
            fprintf(stderr, "error in replying\n");
            exit(EXIT_FAILURE);
        }
        int i = strncmp("Exit", receive, 4);
        if (i == 0)
            break;

        printf("The server message: %s\n", message);

    }

    return 0;
}

Answer 1

char *service; // declared variable name
// ...
sprintf(service, "%d", PORT); // i have tried convert it to char

由于 service 未初始化并且很可能包含无效的指针值，因此对 sprintf() 的调用会导致未定义的行为。

要么在自由存储上分配内存并让service指向它，要么使用足够大小的数组。