examples/getinmemory.c: abort the transfer if not enough memory

No more use exit(3) but instead tell libcurl that no byte has been
written to let it return a `CURLE_WRITE_ERROR`. In addition, check
curl easy handle return code.

docs/examples/getinmemory.c

@@ -42,10 +42,10 @@ WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
   struct MemoryStruct *mem = (struct MemoryStruct *)userp;
 
   mem->memory = realloc(mem->memory, mem->size + realsize + 1);
-  if (mem->memory == NULL) {
+  if(mem->memory == NULL) {
     /* out of memory! */
     printf("not enough memory (realloc returned NULL)\n");
-    exit(EXIT_FAILURE);
+    return 0;
   }
 
   memcpy(&(mem->memory[mem->size]), contents, realsize);
@@ -59,6 +59,7 @@ WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
 int main(void)
 {
   CURL *curl_handle;
+  CURLcode res;
 
   struct MemoryStruct chunk;
 
@@ -84,24 +85,31 @@ int main(void)
   curl_easy_setopt(curl_handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
 
   /* get it! */
-  curl_easy_perform(curl_handle);
+  res = curl_easy_perform(curl_handle);
+
+  /* check for errors */
+  if(res != CURLE_OK) {
+    fprintf(stderr, "curl_easy_perform() failed: %s\n",
+            curl_easy_strerror(res));
+  }
+  else {
+    /*
+     * Now, our chunk.memory points to a memory block that is chunk.size
+     * bytes big and contains the remote file.
+     *
+     * Do something nice with it!
+     *
+     * You should be aware of the fact that at this point we might have an
+     * allocated data block, and nothing has yet deallocated that data. So when
+     * you're done with it, you should free() it as a nice application.
+     */
+
+    printf("%lu bytes retrieved\n", (long)chunk.size);
+  }
 
   /* cleanup curl stuff */
   curl_easy_cleanup(curl_handle);
 
-  /*
-   * Now, our chunk.memory points to a memory block that is chunk.size
-   * bytes big and contains the remote file.
-   *
-   * Do something nice with it!
-   *
-   * You should be aware of the fact that at this point we might have an
-   * allocated data block, and nothing has yet deallocated that data. So when
-   * you're done with it, you should free() it as a nice application.
-   */
-
-  printf("%lu bytes retrieved\n", (long)chunk.size);
-
   if(chunk.memory)
     free(chunk.memory);