“could not resolve host” error in libcurl using c++

Question

The code snippet is as follows:

const int BUFFERSIZE = 50*1024;
char lLoadedData[BUFFERSIZE];
memset(lLoadedData, 0, sizeof(lLoadedData));

mstrURL = "http://www.google.com";
CURL* lCurlHandle = curl_easy_init();
if (lCurlHandle)
{
    //url
    if ((error_code = curl_easy_setopt(lCurlHandle, CURLOPT_URL, mstrURL)) != CURLE_OK)
        return;

    if((error_code = curl_easy_setopt(lCurlHandle, CURLOPT_WRITEDATA, (void *)lLoadedData)) != CURLE_OK)
        return;

    error_code = curl_easy_perform(lCurlHandle);

    if (error_code == CURLE_OK)
    {           
              ...
        }
}

The error_code after executing curl_easy_perform() is CURLE_COULDNT_RESOLVE_HOST.

I have changed the DNS server to 8.8.8.8 and 4.4.4.4, but the error_code is still unchanged.

Does anybody know how to fix this problem? Thanks!

Environment: Windows server 2008, VS 2010.

================update===================== Seems the parameter is wrong. should be: if ((error_code = curl_easy_setopt(lCurlHandle, CURLOPT_URL, mstrURL.c_str())) != CURLE_OK)

My condolences for having to develop on a consumer OS. I can't answer your question, but i can tell you that 4.4.4.4 is unlikely to be a nameserver. You probably meant 8.8.4.4 instead. — fstd
– fstd, Commented Apr 4, 2014 at 6:13
yep, hence my ``I can't answer your question''. You might want to use a platform which allows you to analyze the issue in a structured fashion. On unix, i'd ktrace it to find out what goes wrong exactly, then use a debugger to step through the general location of the error. On Windows, I'd ask Clippy, then call customer support. — fstd
– fstd, Commented Apr 4, 2014 at 6:29

putuyuwono · Accepted Answer · 2015-11-13 04:54:53Z

3

I was having similar error. When I checked the log message by enabling the verbose option, curl tries to rebuild the url whenever I passed it as string. And the rebuild url process produced an invalid url. It only worked when I put the url directly on the curl_easy_setopt method such as: curl_easy_setopt(lCurlHandle, CURLOPT_URL, "http://www.google.com"). The curl would not work if I put the url in a variable and pass it on parameter. But then, I checked the manuals of CURLOPT_URL in here. The url parameter should be char pointer. Therefore, I converted my string url into a char pointer.

So my suggestion is converting your (probably) string mstrURL into char pointer and lets see if it works. If you use std::string, you can use c_str() to convert it to char pointer.

answered Nov 13, 2015 at 4:54

putuyuwono

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Comments

Daniel Stenberg · Accepted Answer · 2014-04-04 07:55:50Z

0

Most probably you're using a proxy that you forgot to tell libcurl about.

You can switch on CURLOPT_VERBOSE to get more info from libcurl about what it does and what happens.

answered Apr 4, 2014 at 7:55

Daniel Stenberg

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