socket connect 函数设置超时

众所周知，在进行网络编程的时候，如果使用系统connect函数，无法设置超时，而在连接一个不存在的主机时，将会一直阻塞。

其实在调用connect函数时，将句柄设置为非阻塞，然后调用select函数，可以达到设置超时的效果。

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1. bool connect(char *host,int port,int timeout)
2. {
3. TIMEVAL Timeout;
4. Timeout.tv_sec = timeout;
5. Timeout.tv_usec = 0;
6. struct sockaddr_in address; /* the libc network address data structure */
8. sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
10. address.sin_addr.s_addr = inet_addr(host); /* assign the address */
11. address.sin_port = htons(port); /* translate int2port num */
12. address.sin_family = AF_INET;
14. //set the socket in non-blocking
15. unsigned long iMode = 1;
16. int iResult = ioctlsocket(sock, FIONBIO, &iMode);
17. if (iResult != NO_ERROR)
18. {
19. printf("ioctlsocket failed with error: %ld\n", iResult);
20. }
22. if(connect(sock,(struct sockaddr *)&address,sizeof(address))==false)
23. {
24. return false;
25. }
27. // restart the socket mode
28. iMode = 0;
29. iResult = ioctlsocket(sock, FIONBIO, &iMode);
30. if (iResult != NO_ERROR)
31. {
32. printf("ioctlsocket failed with error: %ld\n", iResult);
33. }
35. fd_set Write, Err;
36. FD_ZERO(&Write);
37. FD_ZERO(&Err);
38. FD_SET(sock, &Write);
39. FD_SET(sock, &Err);
41. // check if the socket is ready
42. select(0,NULL,&Write,&Err,&Timeout);
43. if(FD_ISSET(sock, &Write))
44. {
45. return true;
46. }
48. return false;
49. }