我尝试运行curl multi interface example：http://curl.haxx.se/libcurl/c/multi-single.html
我正在使用mingw g ++。
首先我收到错误“未定义引用'select @ 20'”。
我在编译器中添加了“-lws2_32”。
现在没有编译错误，但程序打印“select（）返回错误，这是不好的”。
我做错了什么？
#include <stdio.h>
#include <string.h>
/* somewhat unix-specific */
#include <sys/time.h>
#include <unistd.h>
/* curl stuff */
#include <curl/curl.h>
/*
* Simply download a HTTP file.
*/
int main(void)
{
CURL *http_handle;
CURLM *multi_handle;
int still_running; /* keep number of running handles */
curl_global_init(CURL_GLOBAL_DEFAULT);
http_handle = curl_easy_init();
/* set the options (I left out a few, you'll get the point anyway) */
curl_easy_setopt(http_handle, CURLOPT_URL, "http://www.example.com/");
/* init a multi stack */
multi_handle = curl_multi_init();
/* add the individual transfers */
curl_multi_add_handle(multi_handle, http_handle);
/* we start some action by calling perform right away */
curl_multi_perform(multi_handle, &still_running);
do {
struct timeval timeout;
int rc; /* select() return code */
fd_set fdread;
fd_set fdwrite;
fd_set fdexcep;
int maxfd = -1;
long curl_timeo = -1;
FD_ZERO(&fdread);
FD_ZERO(&fdwrite);
FD_ZERO(&fdexcep);
/* set a suitable timeout to play around with */
timeout.tv_sec = 1;
timeout.tv_usec = 0;
curl_multi_timeout(multi_handle, &curl_timeo);
if(curl_timeo >= 0) {
timeout.tv_sec = curl_timeo / 1000;
if(timeout.tv_sec > 1)
timeout.tv_sec = 1;
else
timeout.tv_usec = (curl_timeo % 1000) * 1000;
}
/* get file descriptors from the transfers */
curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
/* In a real-world program you OF COURSE check the return code of the
function calls. On success, the value of maxfd is guaranteed to be
greater or equal than -1. We call select(maxfd + 1, ...), specially in
case of (maxfd == -1), we call select(0, ...), which is basically equal
to sleep. */
rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
switch(rc) {
case -1:
/* select error */
still_running = 0;
printf("select() returns error, this is badness\n");
break;
case 0:
default:
/* timeout or readable/writable sockets */
curl_multi_perform(multi_handle, &still_running);
break;
}
} while(still_running);
curl_multi_remove_handle(multi_handle, http_handle);
curl_easy_cleanup(http_handle);
curl_multi_cleanup(multi_handle);
curl_global_cleanup();
return 0;
}
答案 0 :(得分：0)
你的maxfd返回-1。
http://curl.haxx.se/libcurl/c/curl_multi_fdset.html的摘录：
如果libcurl没有设置文件描述符，则max_fd将包含-1 这个函数返回。否则它将包含更高的描述符 数字libcurl集。当libcurl在max_fd中返回-1时，这是因为 libcurl目前做的事情对你来说是不可能的 使用套接字监视的应用程序，不幸的是你可以 不知道使用select（）完成当前操作的确切时间。 当max_fd以-1返回时，您需要等待一段时间然后继续 并且无论如何都要调用curl_multi_perform。要等多久？我会建议 至少100毫秒，但你可能想在自己的测试中 找到合适价值的特殊条件。
所以，试试延迟：
#if defined(__WIN32__) || defined(_WIN32) || defined(WIN32) || defined(__WINDOWS__) || defined(__TOS_WIN__)
#include <windows.h>
inline void delay( unsigned long ms )
{
Sleep( ms );
}
#else /* presume POSIX */
#include <unistd.h>
inline void delay( unsigned long ms )
{
usleep( ms * 1000 );
}
#endif
#include <stdio.h>
#include <string.h>
/* somewhat unix-specific */
#include <sys/time.h>
#include <unistd.h>
/* curl stuff */
#include <curl/curl.h>
/*
* Simply download a HTTP file.
*/
int main(void)
{
CURL *http_handle;
CURLM *multi_handle;
int still_running; /* keep number of running handles */
curl_global_init(CURL_GLOBAL_DEFAULT);
http_handle = curl_easy_init();
/* set the options (I left out a few, you'll get the point anyway) */
curl_easy_setopt(http_handle, CURLOPT_URL, "http://www.example.com/");
/* init a multi stack */
multi_handle = curl_multi_init();
/* add the individual transfers */
curl_multi_add_handle(multi_handle, http_handle);
/* we start some action by calling perform right away */
curl_multi_perform(multi_handle, &still_running);
do {
struct timeval timeout;
int rc; /* select() return code */
fd_set fdread;
fd_set fdwrite;
fd_set fdexcep;
int maxfd = -1;
long curl_timeo = -1;
FD_ZERO(&fdread);
FD_ZERO(&fdwrite);
FD_ZERO(&fdexcep);
/* set a suitable timeout to play around with */
timeout.tv_sec = 1;
timeout.tv_usec = 0;
curl_multi_timeout(multi_handle, &curl_timeo);
if(curl_timeo >= 0) {
timeout.tv_sec = curl_timeo / 1000;
if(timeout.tv_sec > 1)
timeout.tv_sec = 1;
else
timeout.tv_usec = (curl_timeo % 1000) * 1000;
}
/* get file descriptors from the transfers */
curl_multi_fdset(multi_handle, &fdread, &fdwrite, &fdexcep, &maxfd);
/* In a real-world program you OF COURSE check the return code of the
function calls. On success, the value of maxfd is guaranteed to be
greater or equal than -1. We call select(maxfd + 1, ...), specially in
case of (maxfd == -1), we call select(0, ...), which is basically equal
to sleep. */
while(rc==-1){
delay(1);
rc = select(maxfd+1, &fdread, &fdwrite, &fdexcep, &timeout);
}
switch(rc) {
case -1:
/* select error */
still_running = 0;
printf("select() returns error, this is badness\n");
break;
case 0:
default:
/* timeout or readable/writable sockets */
curl_multi_perform(multi_handle, &still_running);
break;
}
} while(still_running);
curl_multi_remove_handle(multi_handle, http_handle);
curl_easy_cleanup(http_handle);
curl_multi_cleanup(multi_handle);
curl_global_cleanup();
return 0;
}
我希望这会有所帮助。