去掉输入参数的tcping

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/* tcping does a nonblocking connect to test if a port is reachable.

* Its exit codes are:
* -1 an error occured
* 0 port is open
* 1 port is closed
* 2 user timeout

#include <sys/socket.h>#include <netinet/in.h>#include <stdio.h>#include <stdlib.h>#include <errno.h>#include <string.h>#include <unistd.h>#include <sys/time.h>#include <fcntl.h>#include <arpa/inet.h>#define SRV_IP "8.8.8.8"#define SRV_PORT 53int main (int argc, char *argv[]) {int sockfd;struct sockaddr_in addr;int error = 0;int errlen;int ret;struct timeval timeout;fd_set fdrset, fdwset;timeout.tv_sec=10;timeout.tv_usec=0;if((sockfd = socket (AF_INET, SOCK_STREAM, 0)) < 0){printf("socket error.\n");return -1;}memset(&addr, 0, sizeof(addr));addr.sin_family = AF_INET; addr.sin_port = htons(SRV_PORT);if(inet_pton(AF_INET,SRV_IP,&addr.sin_addr) < 0){printf("inet_pton error.\n");close(sockfd);return -1;}fcntl(sockfd, F_SETFL, O_NONBLOCK);if (connect(sockfd, (struct sockaddr *) &addr, sizeof(addr)) != 0) {if (errno != EINPROGRESS) {                printf("%s\n", strerror(errno));                        return (-1);                }FD_ZERO(&fdrset);FD_SET(sockfd, &fdrset);fdwset=fdrset;if ((ret = select(sockfd+1, &fdrset, &fdwset, NULL, &timeout)) == 0) {close(sockfd);printf( "timeout.\n");return(2);}if (FD_ISSET(sockfd, &fdrset) || FD_ISSET(sockfd, &fdwset)) {errlen = sizeof(error);                        if ((ret=getsockopt(sockfd, SOL_SOCKET, SO_ERROR, &error, &errlen)) != 0) {                                printf( "getsockopt error.\n");                                close(sockfd);                                return(-1);                        }                        if (error != 0) {                        printf( "closed.\n");                                close(sockfd);                                return(1);                        }                } else {                        printf("select: sockfd not set\n");close(sockfd);                        return(-1);                }        }printf("connection established.\n ");close(sockfd);return 0;}