方法1，按com口编号循环打开关闭，能打开的就列出。

#include <stdio.h> 
#include <string.h> 
#include <winsock.h> 

int main(int argc, char *argv[]) { 

int mysocket; 

int pcount = 0; 

struct sockaddr_in my_addr; 

WSADATA wsaData; 

WORD wVersionRequested=MAKEWORD(1,1); 


if(argc < 3) { 

printf("usage: %s <host> <maxport>\n", argv[0]); 

exit(1); 

} 


if (WSAStartup(wVersionRequested , &wsaData)){ 

printf("Winsock Initialization failed.\n"); 

exit(1); 

} 


for(int i=1; i < atoi(argv[2]); i++){ 

if((mysocket = socket(AF_INET, SOCK_STREAM,0)) == INVALID_SOCKET){ 

printf("Socket Error"); 

exit(1); 

} 


my_addr.sin_family = AF_INET; 

my_addr.sin_port = htons(i); 

my_addr.sin_addr.s_addr = inet_addr(argv[1]); 


if(connect(mysocket, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == SOCKET_ERROR) 

closesocket(mysocket); 

else{ 

pcount++; 

printf("Port %d - open\n", i); 

}} 


printf("%d ports open on host - %s\n", pcount, argv[1]); 

closesocket(mysocket); 

WSACleanup(); 

return 0; 
}