在 function 调用之后 addrinfo 结构不保留值

Question

I have a static addrinfo struct being used to save the results of my call to getaddressinfo() within the static function init_socket().Inside the init_socket() the addrinfo struct has the correct values, but on return it gets zeroed.

Code below of what I am trying to accomplish.

static struct addrinfo rxRes;

static int init_socket(struct addrinfo *resInfo, char *host, char *port) {
    struct addrinfo hints;
    memset(&hints, 0, sizeof hints);

    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_DGRAM;

    if (!host) { // automatically assign ip to result ip of current machine
        hints.ai_flags = AI_PASSIVE;
    }

    int res = getaddrinfo(host, port, &hints, &resInfo);
    if (res != 0 || !resInfo) {
        PRINT_NET_ERR(res);
        exit(EXIT_FAILURE);
    }

    printf("init addrlen: %d\n", resInfo->ai_addrlen); // correct output

    return socket(resInfo->ai_family, resInfo->ai_socktype, resInfo->ai_protocol);
}

int main(int argc, char *argv[])
{
    /* initialize socket connections */
    int rxsFD = init_socket(&rxRes, TEST_HOST, TEST_PORT);
    printf("main addrlen: %d\n, rxRes.ai_addrlen) // outputs 0
    ...
}

Answer 1

resInfo is a local variable in the function so any changes to it will not be reflected in the caller. The caller needs to pass in a pointer to a pointer and not just a pointer. The getaddinfo will allocate dynamic memory. Yes, it is a little confusing so please see the following corrected code which hopefully makes it clearer.

static int init_socket(struct addrinfo **resInfo, char *host, char *port) {
    ..   
    int res = getaddrinfo(host, port, &hints, resInfo);
    ..
}

int main(int argc, char *argv[])
{
    struct addrinfo *rxRes;
    /* initialize socket connections */
    int rxsFD = init_socket(&rxRes, TEST_HOST, TEST_PORT);
    printf("main addrlen: %d\n, rxRes->ai_addrlen);

    /* free the result when no longer needed */
    freeaddrinfo(rxRes);
    ...
}

Answer 2

Complementing the answer:

I think you will need to use another pointer to access the addrinfo struct inside the function init_socket() for the purpose of the return using the socket() function.

So you can do it:

    struct addrinfo *addrRet = *resInfo;
    printf("initsocket: %d\n", addrRet->ai_addrlen);

    return socket(addrRet->ai_family, addrRet->ai_socktype, addrRet->ai_protocol);

Sorry by the answer. I can't write a comment (no reputation).