Linux下检测tcp所使用的端口

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

void usage(void)
{
    printf("port  \n");
    printf("command:\n");
    printf("-s set the start port\n");
    printf("-e set the end port\n");
    printf("-p set the ip address\n");

    return;
}

int main(int argc,char **argv)
{
    char c;
    char ip[30];
    int startport = 1,endport = 1024;
    int sockfd = -1,i = 0;
    struct sockaddr_in addr;
    float costtime;
    clock_t start,end;

    while ((c = getopt(argc, argv, "?s:e:p:")) > 0)
    {
        switch (c)
        {
            case 's':
                startport = atoi(optarg);
                break;
            case 'e':
                endport = atoi(optarg);
                break;
            case 'p':
                memcpy(ip,optarg,sizeof(ip));
                break;
            default:
                usage();
        }
    }

    if(startport<1 || endport>65535)
    {
        printf("PORT RANGE ERROR!\n");
        return -1;
    }

    printf("Interesting ports %d-%d on %s\n",startport,endport,ip);
    addr.sin_family=AF_INET;
    addr.sin_addr.s_addr=inet_addr(ip);
    start=clock();

    for(i=startport;i<=endport;i++)
    {
        sockfd=socket(AF_INET,SOCK_STREAM,0);
        addr.sin_port=htons(i);
        if(connect(sockfd,(const struct sockaddr *)&addr,sizeof(struct sockaddr_in)) == 0)
        {
            printf("%5d open\n",i);
            close(sockfd);
        }
    }

    end=clock();
    costtime=(float)(end-start)/CLOCKS_PER_SEC;
    printf("\nSmart Nmap finished: %s scanned in %f seconds\n",ip,costtime);

    return 0;
}