const char *分配不正确？

Question

I have the following code:

#define FROM    "<example@gmail.com>"
#define TO      "<example2@gmail.com>"

const char *payload_text[] = {
    "Date: Mon, 29 Nov 2010 21:54:29 +1100\r\n",
    "To: " TO "\r\n",
    "From: " FROM "(Example User)\r\n",
    "Subject: SMTP TLS example message\r\n",
    "MIME-Version: 1.0\r\n",
    "Content-Type: multipart/mixed; boundary=\"KkK170891tpbkKk__FV_KKKkkkjjwq\"\r\n",
    "\r\n",
    "This is a multipart message in MIME format.",
    "\r\n",
    "--KkK170891tpbkKk__FV_KKKkkkjjwq\r\n",
    "Content-Type: text/plain",
    "\r\n",
    "here goes the text message\r\n",
    "\r\n",
    "--KkK170891tpbkKk__FV_KKKkkkjjwq\r\n",
    "Content-Type: image/jpeg; name=\"test.jpg\"\r\n",
    "Content-Transfer-Encoding: base64\r\n",
    "Content-Disposition: attachment; filename=\"test.jpg\"\r\n",
    "\r\n",
    NULL, /*19*/
    "\r\n",
    "--KkK170891tpbkKk__FV_KKKkkkjjwq--\r\n",
    NULL
};

struct upload_status {
    int lines_read;
};

static size_t payload_source(void *ptr, size_t size, size_t nmemb, void *userp) {
  struct upload_status *upload_ctx = (struct upload_status *)userp;
  const char *data;

  if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
    return 0;
  }

  data = payload_text[upload_ctx->lines_read];

  if(data) {
    size_t len = strlen(data);
    memcpy(ptr, data, len);
    upload_ctx->lines_read++;

    return len;
  }

  return 0;
}

std::string readFileToBase64(const char* filename) {
    /* converts binary file to base64 */
}

std::string split76(std::string in) {
    int lines = in.length() / 76;

    for(int i=0;i<lines;i++) {
        in.insert((i+1)*76+i*2, "\r\n");
    }

    return in;
}

int main(void) {
    payload_text[19] = split76(readFileToBase64("C:\\Users\\thrymgjol\\code\\emailtest\\bin\\Release\\test.jpg")).c_str();

  CURL *curl;
  CURLcode res = CURLE_OK;
  struct curl_slist *recipients = NULL;
  struct upload_status upload_ctx;

  upload_ctx.lines_read = 0;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_USERNAME, "example2@gmail.com");
    curl_easy_setopt(curl, CURLOPT_PASSWORD, "legitpassword");
    curl_easy_setopt(curl, CURLOPT_URL, "smtp://smtp.gmail.com:587");
    curl_easy_setopt(curl, CURLOPT_USE_SSL, (long)CURLUSESSL_ALL);
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
    curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
    curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);
    recipients = curl_slist_append(recipients, TO);
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
    curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
    curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
    res = curl_easy_perform(curl);
    if(res != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(res));

    curl_slist_free_all(recipients);
    curl_easy_cleanup(curl);
  }

  return (int)res;
}

However, when I compile and run, payload_source() stops reading payload_text after the 18th indice. This completely cuts off my attachment, which I assign to payload_text[19]. Any ideas on why it does this?

Answer 1

The problem is the value returned from split76 is temporary and is destroyed after the assignment has completed. Any attempt to access it after that results in undefined behavior. If you need to store a pointer to the string buffer you can create local std::string to hold it an ensure it lives long enough to be used.

std::string encodedFile(split76(readFileToBase64("C:\\Users\\thrymgjol\\code\\emailtest\\bin\\Release\\test.jpg")));
payload_text[19] = encodedFile.c_str();