c connect（）错误-参数无效

Question

I'm writing a simple UDP client and an error returned as "invalid argument", but I don't know what's wrong. It is compiled on linux. My code is as below.

int udp_fd = -1;
struct sockaddr_in addr;
int port = 1701;

udp_fd = socket(AF_PPPOX, SOCK_DGRAM, 0);
if (udp_fd < 0) {
    printf("fail to get UDP socket\n");
    return 0;
}

memset((char *) &addr, 0, sizeof(struct sockaddr_in));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("31.25.210.118");
addr.sin_port = htons(port);

if(connect(udp_fd, (struct sockaddr *)&addr, sizeof(addr)) < 0 ) {
    printf("UDP connect failed, errno = %s\n", strerror(errno));
    return 0;
}

Answer 1

You are using an AF_INET address with an AF_PPPoX socket. This is mixing apples and parakeets.

PPP stands for "point-to-point", there is no such thing as IP address in this domain. Pick your game. You either connect over the Internet, and use socket(AF_INET, ... , or connect over PPP and use one of the PPP protocols like PX_PROTO_OLAC or PX_PROTO_OPNS , and a corresponding socket address type ( sockaddr_pppolac or sockaddr_pppopns ) instead of sockaddr_in .