針對libcurl庫的Python導入錯誤

Question

我已經用libcurl在c語言中編寫了一個程序來加載url並將返回值發送給Python（我正在將2個整數從Python傳遞給C。我尚未增強代碼，目前正在嘗試Python和C之間的邏輯和變量可訪問性）。 我能夠成功編譯程序。 當我在Python中加載模塊時，出現錯誤消息“未定義符號：curl_easy_getinfo”。 請讓我知道如何解決此問題。

碼：

#include <Python.h>
#include <stdio.h>
#include <time.h>
#include <stdio.h>
#include <pthread.h>
#include <curl/curl.h>

#define NUMT 4

/*
  List of URLs to fetch.

  If you intend to use a SSL-based protocol here you MUST setup the OpenSSL
  callback functions as described here:

  http://www.openssl.org/docs/crypto/threads.html#DESCRIPTION

*/

const char * const urls[NUMT]= {
  "http://www.google.com",
  "http://www.yahoo.com/",
  "http://www.haxx.se/done.html",
  "http://www.haxx.se/"
};

#define MINIMAL_PROGRESS_FUNCTIONALITY_INTERVAL     3

struct myprogress {
  double lastruntime;
  curl_off_t totdnld;
  void *url;
  CURL *curl;
};

static PyObject *foo1_add(PyObject *self, PyObject *args)
{
    int a;
    int b;
    int s;

    if (!PyArg_ParseTuple(args, "ii", &a, &b))
    {
        return NULL;
    }

    s = sum (a, b);
    return Py_BuildValue("i", s);
   // return Py_BuildValue("i", a + b);
}

static PyMethodDef foo1_methods[] = {
    { "add", (PyCFunction)foo1_add, METH_VARARGS, NULL },
    { NULL, NULL, 0, NULL }
};

PyMODINIT_FUNC initfoo1()
{
    Py_InitModule3("foo1", foo1_methods, "My first extension module.");
}

int sum(int x, int y) {
   int z;

   z = x + y;
   z = geturl (x, y);
   return (z);
}

/* this is how the CURLOPT_XFERINFOFUNCTION callback works */
#ifdef 0
static int xferinfo(void *p,
                    curl_off_t dltotal, curl_off_t dlnow,
                    curl_off_t ultotal, curl_off_t ulnow)
{
  struct myprogress *myp = (struct myprogress *)p;
  CURL *curl = myp->curl;
  double curtime = 0;

  curl_easy_getinfo(curl, CURLINFO_TOTAL_TIME, &curtime);

  /* under certain circumstances it may be desirable for certain functionality
     to only run every N seconds, in order to do this the transaction time can
     be used */
  if((curtime - myp->lastruntime) >= MINIMAL_PROGRESS_FUNCTIONALITY_INTERVAL) {
    myp->lastruntime = curtime;
    fprintf(stderr, "TOTAL TIME: %f \r\n", curtime);
  }

  if (dlnow > 0) {
  fprintf(stderr, "UP: %" CURL_FORMAT_CURL_OFF_T " of %" CURL_FORMAT_CURL_OFF_T
          "  DOWN: %" CURL_FORMAT_CURL_OFF_T " of %" CURL_FORMAT_CURL_OFF_T
          "\r\n",
          ulnow, ultotal, dlnow, dltotal);
  }

  myp->totdnld = myp->totdnld + dlnow;

  if (dlnow > 0) {
  fprintf(stderr, "TOTAL Download: %" CURL_FORMAT_CURL_OFF_T " url is: %s \r\n", myp->totdnld, myp->url);
  }

 // if(dlnow > STOP_DOWNLOAD_AFTER_THIS_MANY_BYTES)
  //  return 1;
  return 0;
}
#endif
/* for libcurl older than 7.32.0 (CURLOPT_PROGRESSFUNCTION) */
static int older_progress(void *p,
                          double dltotal, double dlnow,
                          double ultotal, double ulnow)
{
  return xferinfo(p,
                  (curl_off_t)dltotal,
                  (curl_off_t)dlnow,
                  (curl_off_t)ultotal,
                  (curl_off_t)ulnow);
}

static void *pull_one_url(void *url)
{
  CURL *curl;
  CURLcode res = CURLE_OK;
  struct myprogress prog;

  curl = curl_easy_init();
  if(curl) {
    prog.lastruntime = 0;
    prog.curl = curl;
    prog.url = url;
    prog.totdnld = (curl_off_t) 0;
    curl_easy_setopt(curl, CURLOPT_URL, url);
    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, older_progress);
    /* pass the struct pointer into the progress function */
    curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &prog);
#ifdef 0
#if LIBCURL_VERSION_NUM >= 0x072000
    /* xferinfo was introduced in 7.32.0, no earlier libcurl versions will
       compile as they won't have the symbols around.

       If built with a newer libcurl, but running with an older libcurl:
       curl_easy_setopt() will fail in run-time trying to set the new
       callback, making the older callback get used.

       New libcurls will prefer the new callback and instead use that one even
       if both callbacks are set. */

    curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, xferinfo);
    /* pass the struct pointer into the xferinfo function, note that this is
       an alias to CURLOPT_PROGRESSDATA */
    curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &prog);
#endif
#endif
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);
    res = curl_easy_perform(curl);
    if(res != CURLE_OK)
      fprintf(stderr, "%s\n", curl_easy_strerror(res));
    curl_easy_cleanup(curl);

  }
  return NULL;
}


/*
   int pthread_create(pthread_t *new_thread_ID,
   const pthread_attr_t *attr,
   void * (*start_func)(void *), void *arg);
*/

int geturl(int x, int y)
{
  pthread_t tid[NUMT];
  int i;
  int error;

  /* Must initialize libcurl before any threads are started */
  curl_global_init(CURL_GLOBAL_ALL);

  for(i=0; i< NUMT; i++) {
    error = pthread_create(&tid[i],
                           NULL, /* default attributes please */
                           pull_one_url,
                           (void *)urls[i]);
    if(0 != error)
      fprintf(stderr, "Couldn't run thread number %d, errno %d\n", i, error);
    else
      fprintf(stderr, "Thread %d, gets %s\n", i, urls[i]);
  }

  /* now wait for all threads to terminate */
  for(i=0; i< NUMT; i++) {
    error = pthread_join(tid[i], NULL);
    fprintf(stderr, "Thread %d terminated\n", i);
  }

  return (x * y);
}

Command used for compilation:
gcc -lcurl -lpthread -shared -I/usr/include/python2.7  -fPIC sample.c –o add.so

Error:
>>> import foo1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: ./foo1.so: undefined symbol: curl_easy_perform
>>>

Answer 1

嘗試將-lcurl和-lpthread移至編譯命令中sample.c之后。 鏈接器按從左到右的順序解析符號，因此sample.c引用（例如curl_easy_getinfo ）將從curl_easy_getinfo指定的庫中解析。

順便說一句，使用-pthread比-lpthread更好。 例如，它設置預處理器標志以使某些函數可重入。