CURLcode return codes

Many libcurl functions return a CURLcode. That's a special libcurl typedefed variable for error codes. It returns CURLE_OK (which has the value zero) if everything is fine and dandy and it returns a non-zero number if a problem was detected. There are almost one hundred CURLcode errors in use, and you can find them all in the curl/curl.h header file and documented in the libcurl-errors man page.

You can convert a CURLcode into a human readable string with the curl_easy_strerror() function—but be aware that these errors are rarely phrased in a way that is suitable for anyone to expose in a UI or to an end user:

const char *str = curl_easy_strerror( error );
printf("libcurl said %s\n", str);

Another way to get a slightly better error text in case of errors is to set the CURLOPT_ERRORBUFFER option to point out a buffer in your program and then libcurl will store a related error message there before it returns an error:

char error[CURL_ERROR_SIZE]; /* needs to be at least this big */
CURLcode ret = curl_easy_setopt(handle, CURLOPT_ERRORBUFFER, error);