On Thu, Sep 1, 2011 at 11:42 AM, Tim Johnson <tbj002_at_gmail.com> wrote:
> I've got an application where I'm using cURL in a C program to post data
> read out of a file to a server.  The problem I'm having with it is, the
> curl_slist_append call I'm using seems to be causing a segfault
> intermittently, and seems to vary depending on the machine it is being used
> on.  To demonstrate, I've stripped the program down to the point that it
> isn't actually posting anything anymore.  It is just creating a form and an
> slist, then cleaning it up, and reattempting the same thing.  I've posted it
> below.
> I'm sure I'm doing something wrong here, I just don't know what it is.
>
> Thanks,
> -Tim
> -----------------------------------------------
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>  /* string manip */
> #include <unistd.h>  /* for usleep */
> #include <curl/curl.h>
> #include <curl/types.h>
> #include <curl/easy.h>
>
> int main()
> {
>  CURL *curl;
>
>  struct curl_httppost *formpost=NULL;
>  struct curl_httppost *lastptr=NULL;
>  struct curl_slist *headerlist=NULL;
>  static const char buf[] = "Expect:";
>  char CharArray[] = "This is the text to post....or not.\0";
>  int loop_count = 0;
>  curl_global_init(CURL_GLOBAL_ALL);
>  loop_count = 0;
>  while (1)
>  {
>   {
>    sleep(1);
>    if (loop_count<86400)
>    { loop_count++; }
>    else
>    { loop_count=0; }
>   }
>    printf("\n\nFill out a form to post: %s\n",CharArray);
>    /* Fill in the operation field */
>    curl_formadd(&formpost,
>                 &lastptr,
>                 CURLFORM_COPYNAME, "operation",
>                 CURLFORM_COPYCONTENTS, "PostData",
>                 CURLFORM_END);
>    /* Fill in the file data field */
>    curl_formadd(&formpost,
>                 &lastptr,
>                 CURLFORM_COPYNAME, "filedata",
>                 CURLFORM_COPYCONTENTS, CharArray,
>                 CURLFORM_END);
>
>    /* Fill in the submit field too, even if this is rarely needed */
>    curl_formadd(&formpost,
>                 &lastptr,
>                 CURLFORM_COPYNAME, "submit",
>                 CURLFORM_COPYCONTENTS, "send",
>                 CURLFORM_END);
>    curl = curl_easy_init();
>    /* initalize custom header list  */
>         printf("calling curl_slist_append......\n");
>         headerlist = curl_slist_append(headerlist, buf); /******segfault
> here 2nd time through******/
>         printf("curl_slist_append complete.\n");
>         if(curl)
>    {
>          /* Don't actually do anything with the data for this example */
>          /* however act like we did and start cleanup */
>     curl_easy_cleanup(curl);
>     curl_formfree(formpost);
>
>          printf("About to free slist....\n");
>     curl_slist_free_all (headerlist);
>          printf("slist freed\n\n\n");
>         }
>  }
> }

What do you imagine curl_slist_append() will do with a garbage pointer
headerlist you end up with after curl_slist_free_all() in the second
iteration? The same can be said for the formpost variable.

Lars Nilsson

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Received on 2011-09-01